- Email: [email protected]
Effect of Rennet Coagulation Time on Composition, Yield, and Quality of Reduced-Fat Cheddar Cheese
J. Dairy Sci. 84:1027–1033 American Dairy Science Association, 2001.
Effect of Rennet Coagulation Time on Composition, Yield, and Quality of Reduced-Fat Cheddar Cheese M. E. Johnson, C. M. Chen, and J. J. Jaeggi Wisconsin Center for Dairy Research University of Wisconsin-Madison Madison 53706
ABSTRACT This study compared the effect of coagulum firmness at cutting on composition of 50% reduced-fat Cheddar cheese. Coagulum firmness was determined by subjective evaluation by the cheese maker. Three firmness levels were tested, and these corresponded to average times of coagulant addition to cutting the curd of 25, 48, and 65 min. A slow acid-producing culture was used, and ripening times were altered to give similar curd pH values throughout cheese making. A longer rennet coagulation time (firmer coagulum at cutting) resulted in an increase in cheese moisture as well as an increase in cheese yield. The percentages of fat recovered in the cheese decreased with increasing curd firmness. The percentage of nitrogen recovered in the cheese was similar among the treatments. The amount of whey collected from the curd after milling increased as the coagulum firmness at cutting increased. Higher moisture content and lower pH of cheese made from the firmer curd at cutting contributed to softer, smoother-bodied cheeses, but the Cheddar flavor intensity was not affected. (Key words: reduced-fat Cheddar, rennet coagulation time, moisture, cheese yield) INTRODUCTION A goal of reduced-fat cheese manufacturers is to produce a product that is similar in flavor, melt, firmness, and texture to the full fat cheese that they are trying to emulate. However, the manufacture of reduced-fat cheeses requires modification of the cheese-making protocol to achieve these goals. A key to the successful manufacture of reduced-fat cheeses (or any cheese) is to control the chemical changes that occur to the casein molecules during manufacture and subsequent ripening. Cheese composition and ultimately the interaction
Received September 11, 2000. Accepted December 26, 2000. Corresponding author: M. E. Johnson; e-mail: [email protected]. edu.
between casein molecules and adjacent micelles determines the firmness, melt, and chewiness of a cheese (Prentice et al., 1993). The interaction between casein molecules is ultimately determined by ionic charge on the casein molecules (electrostatic repulsion), hydrophobicity of the casein, hydration of the casein (due to ionization of the casein), bound calcium phosphate, temperature, and proteolysis (Roefs et al., 1990). These are strongly influenced by the rate and extent of acid development (pH) at each step in the manufacturing process and ionic strength of the serum phase (mostly sodium chloride and ionic calcium). Of particular importance are the pH at rennet addition, whey separation, and the lowest pH obtained in the cheese. The lower the pH at the time of rennet coagulation or the lower the pH of the cheese, the less bound calcium and (to a point) greater casein hydration. It follows that the higher the moisture and lower the bound calcium, the softer the cheese and to a point, the greater the melt (Kellar et al., 1974). If the pH is lowered to <5.0 or the cheese is heated, the casein molecules do not associate as much with the water and begin to rearrange into large aggregates with free serum forming between the casein aggregates. The casein molecules within the aggregates interact more closely, but the interaction between aggregates is less. The cheese becomes brittle (grainy) but less chewy, there is a loss of stretch, and there is an increase in the release of fat and serum if the cheese is warmed. To overcome the problem of excessive firmness and poor melt properties often associated with a reducedfat cheese, manufacturing protocols must be adjusted (usually to obtain a lower final cheese pH, or lower pH at rennet addition) to obtain the appropriate level of bound calcium, casein hydration, and proteolysis. These adjustments, coupled with manufacturing practices that increase moisture content, are being used commercially to produce reduced-fat and light cheeses that are similar in melt, firmness, chewiness, and texture to higher fat varieties. Conversely most body and performance defects often associated with reduced-fat cheeses are due to inappropriate manufacturing protocol.
1027
1028
JOHNSON ET AL.
To attain a higher moisture cheese, the cheese-making protocol is adjusted to restrict syneresis. An effective method of increasing cheese moisture involves rinsing the curd with water that is lower in temperature than the curd. Cold curd (cheese) will hold water. The water is eventually absorbed by the cheese casein network under suitable conditions. These conditions are governed by the charge on the casein molecules (loss of calcium), pH, ionic strength, and temperature (van Vliet and Walstra, 1994). While rinsing initially improves the physical properties of reduced-fat cheeses, it may produce a cheese that lacks Cheddar flavor, and the cheese may develop a weaker, pasty body during aging (Johnson and Chen, 1995). Other manufacturing methods used to increase cheese moisture include incorporation of denatured serum proteins (high milk heat treatment, use of concentrated milks, whey protein concentrate added directly or via starter media, addition of starch or other fat mimetics), firmer coagulum at cutting, lower pH at rennet addition, larger curd particle size at cutting, less stir-out after cutting, reduced acid development during stir-out, less stir-out time after whey and curd separation, and lower cook temperatures. More recent techniques include homogenization of the cream (Metzger and Mistry, 1994) and use of exopolysaccharide-producing bacteria (Low et al., 1998). Aleandri et al. (1989) found that an increase in curd firmness at cutting increased cheese yield (increased moisture) but lowered fat recovery. Several other research groups evaluated the effect of milk coagulum firmness at cutting in full fat Cheddar cheese. Results were varied. Mayes and Sutherland (1989) found that cheese moisture increased when the coagulum for Cheddar cheese was cut at 200% of the control setting time. However, Bynum and Olson (1982) found no significant differences in cheese moisture after milk coagulum setting times were increased from 28 to 47 min. Banks and Muir (1984) concluded that the firmness of renneted gels at cutting was not directly related to cheese yield or process efficiency. Others (Mayes and Sutherland, 1989; Riddel-Lawrence and Hicks, 1989) demonstrated that after cutting the coagulum, a healing time before agitation influenced cheese moisture and yield more than did milk gel firmness at cutting. Johnston et al. (1991) showed that a combination of speed and duration of cutting and the subsequent speed of stirring prior to cooking can influence fat recovery and curd fines. Thus, some of the discrepancy between published reports may be due to manufacturing practices after the curd is cut. The expected difference in moisture retention in a cheese that is produced from a soft coagulum versus a firm coagulum at cutting would be less in a full fat Cheddar cheese than in a lower fat Cheddar Journal of Dairy Science Vol. 84, No. 5, 2001
cheese. One reason for this is the physical characteristics of the clot (Lagoueyte et al., 1994; Zoon et al., 1988a, 1988b) and curd. In addition, small differences may not be found to be statistically significantly different if the variation between trials is large. During coagulation, casein micelles first form chains, then small aggregates, and then larger aggregates (Roefs et al., 1990). The space (pores) between the aggregates is filled with fat and serum. The more fat globules, the greater the space between casein aggregates. As the clotting process continues, individual groups of aggregates become larger, serum is forced out of the aggregates, and the coagulum becomes firmer. The space between aggregates concomitantly increases in size, further limiting the contact between aggregates. If the coagulum is cut soft, the potential for the aggregates to react with each other is greater than if the coagulum is cut firm due to the proximity of the aggregates. Fat at the surface of the curd particle is lost upon agitation. With the loss of fat and with the pressure exerted on the curd during stirring, there is a collapse of the pore allowing for an increase in reaction between aggregates. In turn, syneresis is increased, and a “skin” is formed on the outside of the curd particle. Until the skin is formed, fat within the pore can be lost to the whey, and the curd particle is more susceptible to the rigors of agitation. The curd is more brittle and breaks apart more readily. Consequently, a coagulum that is cut soft will lose less fat and serum than a coagulum that is cut firm if sufficient time is allowed for formation of the skin. The amount of fat and casein loss is dependent on the cutting mechanism. Higher losses occur with manual cutting than with mechanical cutting (Johnston et al., 1991). If the soft coagulum is agitated before the skin develops, the curd will break up, leading to more curd fines and greater fat loss. With an increase in curd fines, more nitrogen is lost to the whey. As the casein content in the milk increases, the coagulum forms faster and subsequently will be firmer than lower casein milks if the temperature, calcium ion activity, time, and pH of coagulation are the same (Green and Grandison, 1993). Indeed, to slow the rate of aggregation, concentrated milks (higher in casein) can be set at lower temperatures. After the whey is separated from the curd, it is either continually stirred (stirred curd Cheddar process) or allowed to mat (milled curd Cheddar). In stirred curd Cheddar, the longer the curd is stirred the greater the moisture loss. If the curd is allowed to mat, it will retain more moisture, but serum and fat are lost after milling as new surface area is exposed. Subsequent salting and stirring of the milled curd exacerbates the moisture and fat loss. This paper will focus on the use of increased coagulum firmness at cutting as a method to increase
RENNET COAGULATION TIME AND CHEESE YIELD Table 1. Cheese manufacturing protocol for 50% reduced-fat Cheddar cheese. Rennet coagulation time (min)1 25
48
65
pH
Total elapsed time Initial milk Add starter Add coagulant Cut Drain Mill Add salt
43 68 103 201 219
0 ± ± ± ± ±
5 1 6 14 14
0 20 ± 68 ± 102 ± 196 ± 214 ±
2 7 8 6 7
0 5 ± 70 ± 107 ± 199 ± 217 ±
0 4 5 8 6
6.61 6.56 6.54 6.50 6.36 5.91 5.82
± ± ± ± ± ± ±
0.03 0.03 0.03 0.03 0.02 0.01 0.04
Coagulation time = Addition of coagulant to cut.
1
moisture content in reduced-fat Cheddar cheese. The effect of coagulum firmness on fat and nitrogen retention in whey, pressed whey, and cheese is also determined. MATERIALS AND METHODS Cheese Manufacturing Table 1 contains an outline of the cheese manufacturing schedule. A licensed Wisconsin cheese maker manufactured the cheese in the University of Wisconsin dairy processing pilot plant. Raw whole milk was skimmed to approximately 1.3% fat, pasteurized at 73°C for 16 s, and stored overnight at 3°C. The next morning, 249.7kg portions of milk were heated to 43°C; the milk was then cooled to a ripening temperature of 32°C. A single strain of Lactococcus lactis ssp. cremoris (D11; RhoˆnePoulenc, Madison, WI) grown in LF media (RhoˆnePoulenc), held overnight at 7°C, pH 4.40, was inoculated into cheese milk at a rate of 1.25% (wt/wt). This is a slow acid-producing culture. We hoped this would minimize any pH differences during variations in the time of rennet coagulation. Five minutes before the addition of the milk coagulant, 49 ml of calcium chloride (32% solution; Rhoˆne-Poulenc) was added. Doublestrength chymosin (Chymax, Pfizer, Milwaukee, WI) was added at the rate of 19 ml per 250 kg of milk. The time from adding the starter to rennet addition was varied to ensure that all treatments were cut, drained, milled, and salted at the same time and curd pH. An experienced licensed cheese maker subjectively evaluated the firmness level of the coagulum at cutting. The cheese maker did not cut by time but by his evaluation of the coagulum firmness. It coincidentally turned out that there was little variation in actual cutting time. The cheese maker was unaware of the time until the curd was cut. The coagulum was cut with 0.95-cm knives at a pH of 6.5, and the curd was given a 5-min healing time, followed by 10 min of gentle agitation
1029
before heating started. The temperature of the curdwhey slurry was raised from 32 to 38°C over 25 min. After reaching cooking temperature, the whey was slowly drained. Cheese slabs were cheddared, piled two high, and then milled at a curd pH of 5.9. Fifteen minutes after milling, curd was salted at a rate of 2.50 g of flake salt/kg of milk. Curd was packed into 9-kg Wilsonstyle hoops and pressed for 4 h at ambient temperature. Cheddar blocks were weighed, vacuum-packaged, and aged at 7°C. Analysis All compositional tests were in duplicate. Whey samples were collected 5 min after the start of draining. Press whey samples were a composite of whey collected from milling through pressing of the cheese. Milk, whey, and press whey samples were analyzed for fat by Mojonnier (Marshall, 1992) protein (total percentage of N × 6.38) by Kjeldahl (AOAC, 1995), and casein by the International Dairy Federation procedure (IDF, 1964). Milk was also tested for NPN by weighing a 15-g sample and mixing it with 5 g of 48% TCA. After 30 min at 25°C, the mixture was filtered (Whatman no. 1 filter paper; Whatman Corp., Clifton, NJ). The clear filtrate was weighed, and protein (percentage of N × 6.38) was determined by Kjeldahl (AOAC, 1995). Cheeses were sampled by removing a 2-cm slab of cheese from the end of the block, and then cutting another 1-cm slab of cheese from the block for analysis. Cheese was analyzed for moisture by vacuum oven (Vanderwarn, 1989), fat by Babcock (Marshall, 1992), pH by the quinhydrone method (Van Slyke and Price, 1979), salt by chloride electrode (model 926; Corning Glass Works, Medfield, MA; Johnson and Olson, 1985), and protein by Kjeldahl (AOAC, 1995). Cheese Yield Calculations Milk was weighed to ±0.1 kg (model 31-1822-FD; Toledo Scale Company, Toledo, OH), press whey was weighed to ±0.001 kg (Mettler PJ6; Mettler Instrument Corp., Highstown, NJ), and cheese was weighed to ±0.045 kg (model 2071; Toledo Scale Company). The weight of the whey was calculated by subtracting the weight of the cheese and press whey from the weight of the milk. The percentage of fat or N recovered in the cheese was the total amount of fat or N in the cheese divided by the total amount of fat or N in the milk. Sensory Evaluation Descriptive taste panels consisted of six to 10 experienced judges who evaluated the cheese for flavor and Journal of Dairy Science Vol. 84, No. 5, 2001
1030
JOHNSON ET AL.
Table 2. Average milk composition used for the manufacture of 50% reduced-fat Cheddar cheese. Analysis % Milk fat Total solids Total protein1 % NPN True protein2 % NCN Casein3 C:F ratio
1.285 10.12 3.243 0.035 3.018 0.115 2.512 1.955
± ± ± ± ± ± ± ±
0.033 0.07 0.043 0.002 0.037 0.002 0.047 0.065
Total % Nitrogen × 6.38. (Total % Nitrogen − % NPN) × 6.38 3 (Total % Nitrogen − % NCN) × 6.38
making day and time from rennet addition to cutting the coagulum. Cheese-making day reflected differences, mainly due to variation in milk composition. Standard error of the means was derived from the error mean square term of the ANOVA. A Fisher’s protected least significant difference was calculated to evaluate differences between treatment means when P < 0.05. Sensory data was analyzed using the SAS PROC GLM method (1990).
1
RESULTS
2
Cheese Manufacturing
body characteristics using category scaling. Judges evaluated the following flavor attributes: Cheddar flavor intensity (1 = none to 7 = aged), acid flavor intensity (1 = flat to 7 = pronounced), and intensity of bitterness and off-flavors (1 = none to 7 = pronounced). Body analysis included: body (1 = very soft to 7 = very firm), and smoothness (1 = very curdy to 7 = very smooth). The taste panelists first scored the control cheese (rennet coagulation time of 23 min), and gave it a consensus rating in all categories. Random numbers were assigned to the cheeses, including the control cheeses. Judges scored cheese attributes using the reference (consensus) as a guide. Experimental Design and Statistical Analysis On a single cheese-making day, three vats of reducedfat Cheddar cheese were manufactured using one lot of milk split into three portions. On each day, each of the different coagulum firmness levels were tested. The firmness level was a subjective evaluation by an experienced licensed cheese maker. The cheese maker did not cut by time and was unaware of the time until the curd was cut. Cheese making was replicated on eight separate days for a total of 24 vats of cheese. Statistical analysis for cheese composition and cheese yield were completed by the statistical method described by Emmons and Binns (1990) using the SAS system (1990). The independent variables in the model were cheese-
Total cheese-making time for all vats from starter addition to salting was completed in approximately 3 h and 35 min (Table 1). The slow rate of acid development by the starter ensured that all treatments were cut, drained, milled, and salted at approximately the same time and curd pH. Milk, Whey, and Cheese Composition Milk composition is shown in Table 2. Table 3 presents composition of whey and press whey. Percentages of nitrogen in whey and in press whey did not differ as a result of the rennet coagulation time. Significant differences were noted in the percentages of fat in the whey and press whey. Cheese composition as analyzed from samples collected at 3 d is given in Table 4. Moisture increased as the rennet coagulation time increased (P < 0.05) Subsequently, cheese fat, protein, and salt contents in the cheese also differed (P < 0.05). After 2 wk of aging, the control cheeses were higher in pH than cheeses with the higher moisture content (Table 5). Fat and Protein Recovery Table 4 presents actual weights (milk, cheese, and press whey), calculated weights (whey weight is milk weight minus cheese weight and weight of press whey), and percentages of fat and N recoveries. The rennet coagulation time directly affected the rate at which whey was expelled from the curd, as shown by differ-
Table 3. Composition of whey and pressed whey collected during manufacture of reduced-fat Cheddar cheese Rennet coagulation time
Whey % Fat
% Nitrogen
% Fat
% Nitrogen
25 min 48 min 65 min
0.156 ± 0.008 0.160b ± 0.014 0.175a ± 0.015
0.142 ± 0.005 0.141a ± 0.007 0.140a ± 0.008
0.386 ± 0.028 0.349b ± 0.026 0.343b ± 0.036
0.143a ± 0.009 0.140a ± 0.007 0.145a ± 0.008
b
Pressed whey
a
a
Means in the same row having different superscripts are significantly different (P < 0.05).
a,b
Journal of Dairy Science Vol. 84, No. 5, 2001
1031
RENNET COAGULATION TIME AND CHEESE YIELD Table 4. Average composition, fat, and nitrogen recovery for 50% reduced-fat Cheddar cheese. Rennet coagulation time (min) 25 % % % % %
Moisture Fat Protein1 Salt FDM
46.44 14.68 32.08 1.77 27.41
% Fat recovery, cheese % Fat recovery, whey % Fat recovery, pressed whey % Fat recovery, total % Nitrogen recovery, cheese % Nitrogen recovery, whey % Nitrogen recovery, pressed whey % Nitrogen recovery, total Whey weight (kg)2 Pressed whey weight (kg) Total yield (kg)
48 ± ± ± ± ±
0.98a 0.42a 0.68a 0.06a 0.72a
48.29 14.18 31.04 1.75 27.41
65 ± ± ± ± ±
0.80b 0.44b 0.80b 0.10a 0.56a
48.90 13.86 30.92 1.61 27.11
± ± ± ± ±
1.17c 0.56c 0.75b 0.15b 0.61b
88.1 ± 0.7a 11.1 ± 0.5a
87.7 ± 1.0a 11.2 ± 0.8a
86.4 ± 1.3b 12.2 ± 0.9b
0.5 ± 0.1a 99.6 ± 0.9
0.6 ± 0.2a 99.5 ± 1.0
0.8 ± 0.2b 99.3 ± 1.0
74.6 ± 0.9a 25.2 ± 0.7a
74.4 ± 1.0a 24.7 ± 1.0a
74.3 ± 1.6a 24.8 ± 1.0a
0.4 ± 0.0a 100.3 ± 0.9
0.6 ± 0.2b 99.7 ± 0.6
0.8 ± 0.1c 99.9 ± 1.0
229.79 ± 0.67a 4.02 ± 0.48a 19.42 ± 0.27a
227.58 ± 1.36b 5.63 ± 1.35b 20.04 ± 0.41b
225.92 ± 1.65c 7.10 ± 1.26c 20.19 ± 0.52b
Means in the same row having different superscripts are significantly different (P < 0.05). % Total nitrogen × 6.38. 2 Whey = (milk + starter − cheese + salt − pressed whey) Milk + starter weight was a constant at 252.90kg. a,b,c 1
ences in the mean weights of the whey and press whey. As the rennet coagulation time increased, there was a decrease in the amount of whey collected before milling and an increase in the amount of whey collected after milling and pressing. However, the slight increase in volume of whey expelled during pressing would result in a slight increase in the loss of fat, nitrogen, and salt. The total percentages of fat and N recovered did not differ. A greater (P < 0.05) percentage of fat was recovered in the whey and press whey, and less fat was recovered in the cheese when the milk had a rennet coagulation time of 65 min. There were no differences in fat recovery in cheese, whey, or press whey between milks with a rennet coagulation time of 25 or 48 min. The percentage of N recovered in cheese tended to decrease with increasing coagulum firmness at cutting, but the difference was not statistically significant. There were greater N losses in the press whey, with an increase in coagulum firmness at cutting. This is
Tablel 5. Cheese pH during 26 wk for 50% reduced-fat Cheddar cheese. Rennet coagulation time (min)
Cheese age (wk) 0.5
2
6
13
26
25 48 65
5.39 5.33 5.28
5.19 5.10 5.04
5.21 5.05 5.04
5.18 5.04 5.00
5.20 5.08 5.07
due to the larger volumes of whey expelled after milling. However, the sum of N recovered in the whey and press whey did not differ among treatments.
Cheese Yield There was an increase in cheese yield as the coagulum firmness increased. The increase was due to an increase in the moisture content of cheese. The additional serum solids that would accompany the increase in moisture would also contribute to an increase in cheese yield, albeit too small to measure at the small difference in moisture observed in our experiments.
Sensory Evaluation Table 6 contains the results of the descriptive taste panels at 3 and 6 mo. Rennet coagulation time did not affect Cheddar flavor intensity throughout aging. However, judges noted an increase in the acid flavor intensity and smoothness (less curdy) and a decrease in firmness in cheeses made from milk with a rennet coagulation time longer than 25 min. Although the cheeses made from milk with a rennet coagulation time of 65 min developed more bitterness and off-flavor intensity at 6 mo than did the other cheeses, the intensity of these flavors would be described as very slight to slight. Journal of Dairy Science Vol. 84, No. 5, 2001
1032
JOHNSON ET AL. Table 6. Descriptive taste panel results for 50% reduced-fat Cheddar cheese cut at different milk coagulum firmness at 3 and 6 mo of aging. Sixteen panels were conducted, each consisting of 6 to 10 experienced judges. Data are the means of the 8 taste panels conducted at each age. Rennet coagulation time Cheese at 3 mo of age 25 48 65 Cheese at 6 mo of age 25 48 65
Cheddar flavor intensity1
Acid flavor intensity2
Bitter flavor intensity3
Off-flavor intensity3
Body4
Smoothness5
2.4a 2.5a 2.5a
3.1a 3.5b 3.8c
1.7a 1.7a 1.9a
2.4a,b 2.3b 2.8a
5.2a 4.0b 3.7b
2.7a 3.7b 4.0b
3.2a 3.5a 3.4a
3.5a 3.8a 4.0a
2.3a 2.3a 2.6b
2.8a 3.0a 3.2b
4.4a 3.8b 4.0b
3.8a 4.5b 4.3b
Means in the same column having different superscripts are significantly different (P < 0.05). Cheddar flavor intensity: 2 = very mild, 3 = mild, and 4 = mild to medium. 2 Acid flavor intensity: 3 = ideal acid, and 4 = slight acid. 3 Bitter and off-flavor intensity: 1 = none, 2 = very slight, 3 = slight, and 4 = slight to definite. 4 Body: 3 = slight soft, 4 = neither soft nor firm, and 5 = slight firm. 5 Smoothness: 3 = slight curdy, 4 = neither curdy nor smooth, and 5 = slight smooth. a,b,c 1
DISCUSSION Cheese Moisture and Fat Recovery As expected, increasing the coagulum firmness at cutting significantly increased cheese moisture and cheese yield. However, it also resulted in more fat lost to the whey during manufacture. These results can be attributed to the rigidity and structure (pore and casein aggregate size) of the network (Lagoueyte et al., 1994). Milling the curd increases the surface area of the slabs of cheddared curd. Fat is released from the newly exposed surface. It follows that a more porous curd (as the result of a more rigid coagulum) will release more fat, serum, and whey upon subsequent pressing than a curd produced from a coagulum that was softer when cut. In our experiments, the time from cutting the coagulum to putting the salted curd into hoops for pressing was the same for all cheeses. We also used the milled curd method of making Cheddar cheese. If we had used a stirred curd method of making Cheddar cheese, the differences in moisture between the cheeses may not have been as noticeable. The stirred curd process (or dry stir-out) is often used to reduce moisture in cheese as it exposes more surface area to evaporation. In addition, the weight of the curds on each other helps to collapse the space between aggregates of micelles and results in loss of serum from the curd particle. Serum lost from individual curd particles (via syneresis) is more easily drained from the curd and is not trapped within a mass of curd as in the cheddaring process. Sensory Attributes As anticipated, the increased moisture content resulted in a softer, smoother Cheddar cheese. The effect Journal of Dairy Science Vol. 84, No. 5, 2001
is not due to an increase in moisture per se, but to an increase in casein hydration. Higher cheese moisture will result in more sugar in the curd, which in turn will lead to more acid development (more acid tasting cheese). This leads to a slightly lower cheese pH, and a decrease in bound calcium. Subsequently, an increase in casein hydration occurs, and an increase in casein mobility (able to rearrange) and a less curdy cheese. A more hydrated casein is also more prone to proteolysis. In addition, the residual chymosin would be more active at the lower pH. Increased chymosin activity would lead to a softer cheese but may increase bitterness. CONCLUSION Our results are consistent with the model described in the introduction. As this model predicted, increasing the curd firmness as cutting (increased rennet coagulation time) increased moisture content of the cheese but decreased fat recovery. In addition, there was more whey and fat lost at pressing, with increasing curd firmness at cutting. The increase in moisture offset the decrease in fat recovery resulting in higher cheese yields. In our method of cheese manufacture, the stirout time is minimized and the curd is cheddared not stirred. Stirred-curd cheese may be lower in moisture than cheddared cheese. This depends on the duration of stirring of the curd after whey drainage. The increased moisture and physico-chemical changes that occur to the casein (due to a decrease in pH), undoubtedly resulted in a more acid, less firm, and smoother cheese. There will be a limit to the amount of increase in moisture obtained through increasing the rennet coagulation time. There will also be a point at which increasing coagulum firmness at cutting will not result in an in-
RENNET COAGULATION TIME AND CHEESE YIELD
crease in moisture in cheese. In addition, unless other manufacturing steps are not carefully controlled, the increase in moisture obtained through cutting at a firmer coagulum will be negated. We have observed that incorporation of a cold-water rinse is more effective at increasing moisture content of the cheese than is increasing the firmness of the coagulum at cutting. The protocol that we used to make reduced-fat Cheddar did not include any means to reduce the lactose content of the cheese, i.e., whey dilution or curd rinsing. A higher pH at coagulant addition, draining, milling, and salting (than in a typical Cheddar manufacturing protocol), will keep an important buffering compound in the cheese (calcium phosphate), and it will not be lost in the whey. In addition, the phosphoserine in the casein remains unprotonated or associated with calcium phosphate and maintains its buffer potential. Calcium phosphate is released from the casein (phosphoserine) as the pH is lowered. This results in the retention of calcium phosphate in the cheese. Therefore even though there is far more acid in the cheese, there is also more buffering capacity. The phosphate becomes protonated, and at pH above 5.0 the casein will become more hydrated and softer. In addition the casein will be more prone to proteolysis resulting in a softer cheese. ACKNOWLEDGMENTS The authors thank Sonia Cotto-Febo, Amy Dikkeboom, Ann Kieslich, Al Muelling, Ellen Shumaker, and Chris Simon for their assistance and support in cheese making and analytical work. Authors are also appreciative of Bill Klein and other workers in the University of Wisconsin-Madison Dairy Plant for milk processing. The Wisconsin Center for Dairy Research and the National Dairy Promotion and Research Board funded this project. REFERENCES Aleandri, R., J. C. Schneider, and L. G. Buttazzoni. 1989. Evaluation of milk for cheese production based on formagraph measures. J. Dairy Sci. 72:1967–1975. Association of Official Analytical Chemists. 1995. Official Methods of Analysis. 16th ed. AOAC, Arlington, VA. Banks, J. M., and D. D. Muir. 1984. Coagulum strength and cheese yield. Dairy Ind. Int. 39:17,19,21,36. Bynum, D. G., and N. F. Olson. 1982. Influence of curd firmness at cutting on Cheddar cheese yield and recovery of milk constituents. J. Dairy Sci. 65:2281–2290. Emmons, D. B., and M. Binns. 1990. Cheese yield experiments and proteolysis by milk-clotting enzymes. J. Dairy Sci.73:2028–2043.
1033
Green M. L., and A. S. Grandison. 1993. Secondary (non-enzymatic) phase of rennet coagulation and post-coagulation phenomena. Pages 101–140 in Cheese: Chemistry, Physics, and Microbiology. P. F. Fox ed. Chapman and Hall, London, UK. International Dairy Federation. 1964. Determination of the casein content of milk. Int. Dairy Fed. Standard 29. Int. Dairy Fed., Brussels, Belgium. Johnson, M. E., and C. M. Chen. 1995. Technology of manufacturing reduced-fat Cheddar cheese. Pages 331–337 in Chemistry of Structure-Function Relationships in Cheese. E. L. Malin and M. H. Tunick, ed. Plenum Press, New York. Johnson, M. E., and N. F. Olson. 1985. A comparison of available methods for determining salt levels in cheese. J. Dairy Sci. 68:1020–1024. Johnston, K. A., F. P. Dunlap, and M. F. Lawson. 1991. Effects of speed and duration of cutting in mechanized Cheddar cheesemaking on curd particle size and yield. J. Dairy Res. 58:345:354. Kellar, B., N. F. Olson, and T. Richardson. 1974. Mineral retention and rheological properties of Mozzarella cheese made by direct acidification. J. Dairy Sci. 57:174–180. Lagoueyte, N., J. Lablee, A. Lagaude, and B. Tarodo de la Fuente. 1994. Temperature affects microstructure of renneted milk gel. J. Food Sci. 59:956–959. Low, D., J. A. Ahlgreen, D. Horne, D. J. McMahon, D. J. Oberg, and J. F. Broadbent. 1998. Influence of Streptococcus thermophilus MC-1C capsular exopolysaccharide on cheese moisture levels. Appl. Environ. Microbiol. 64:2147–2151. Marshall, R. T., ed. 1992. Standard Methods for the Examination of Dairy Products. 16 th ed. Am. Publ. Health Assoc., Inc. Washington, D. C. Mayes, J. J., and B. J. Sutherland. 1984. Coagulum firmness and yield in Cheddar cheese manufacture—the role of the curd firmness instrument in determining cutting time. Aust. J. Dairy Technol. 39:69–73. Mayes, J. J., and B. J. Sutherland. 1989. Further notes on coagulum firmness and yield in Cheddar cheese manufacture. Aust. J. Dairy Technol. 44:47–48. Metzger, L. E., and V. V. Mistry. 1994. A new approach using homogenization of cream in the manufacture of reduced fat Cheddar cheese. Manufacture, composition, and yield. J. Dairy Sci. 77:3506–3515. Prentice, J. H., K. R. Langley, and R. J. Marshall. 1993. Cheese rheology, Pages 303–340 in Cheese: Chemistry, Physics, and Microbiology. P. F. Fox ed. Chapman and Hall, London, UK. Roefs, S.P.F.M., T. van Vliet, H.J.C.M. van den Bijgaart, A.E.A. de Groot-Mostert, and P. Walstra. 1990. Structure of casein gels made by combined acidification and rennet action. Neth. Milk Dairy J. 44:159–188. Riddel-Lawrence, S., and C. L. Hicks. 1989. Effect of curd firmness on stirred curd cheese yield. J. Dairy Sci. 72:313–321. SAS User’s Guide: Statistics, Version 6.0 Edition. 1990. SAS Inst., Inc., Cary, NC. Vanderwarn, M. A. 1989. M.S. Thesis. Analysis of cheese and cheese products for moisture. University of Wisconsin, Madison Van Slyke, L. L., and W.V. Price. 1979. Cheese. Ridgeview Publ. Co., Atascadara, CA. van Vliet, T., and P. Walstra. 1994. Water in casein gels; how to get it out or keep it in. J. Food Enginering. 22:75–88. Zoon, P., T. van Vliet, and P. Walstra. 1988a. Rheological properties of rennet-induced skim milk gels. 1. Introduction. Neth. Milk Dairy J. 42:249–269. Zoon, P., T.van Vliet, and P. Walstra. 1988b. Rheological properties of rennet-induced skim milk gels. 2. The effect of temperature. Neth. Milk Dairy J. 42:271–294
Journal of Dairy Science Vol. 84, No. 5, 2001
Effect of Rennet Coagulation Time on Composition, Yield, and Quality of Reduced-Fat Cheddar Cheese M. E. Johnson, C. M. Chen, and J. J. Jaeggi Wisconsin Center for Dairy Research University of Wisconsin-Madison Madison 53706
ABSTRACT This study compared the effect of coagulum firmness at cutting on composition of 50% reduced-fat Cheddar cheese. Coagulum firmness was determined by subjective evaluation by the cheese maker. Three firmness levels were tested, and these corresponded to average times of coagulant addition to cutting the curd of 25, 48, and 65 min. A slow acid-producing culture was used, and ripening times were altered to give similar curd pH values throughout cheese making. A longer rennet coagulation time (firmer coagulum at cutting) resulted in an increase in cheese moisture as well as an increase in cheese yield. The percentages of fat recovered in the cheese decreased with increasing curd firmness. The percentage of nitrogen recovered in the cheese was similar among the treatments. The amount of whey collected from the curd after milling increased as the coagulum firmness at cutting increased. Higher moisture content and lower pH of cheese made from the firmer curd at cutting contributed to softer, smoother-bodied cheeses, but the Cheddar flavor intensity was not affected. (Key words: reduced-fat Cheddar, rennet coagulation time, moisture, cheese yield) INTRODUCTION A goal of reduced-fat cheese manufacturers is to produce a product that is similar in flavor, melt, firmness, and texture to the full fat cheese that they are trying to emulate. However, the manufacture of reduced-fat cheeses requires modification of the cheese-making protocol to achieve these goals. A key to the successful manufacture of reduced-fat cheeses (or any cheese) is to control the chemical changes that occur to the casein molecules during manufacture and subsequent ripening. Cheese composition and ultimately the interaction
Received September 11, 2000. Accepted December 26, 2000. Corresponding author: M. E. Johnson; e-mail: [email protected]. edu.
between casein molecules and adjacent micelles determines the firmness, melt, and chewiness of a cheese (Prentice et al., 1993). The interaction between casein molecules is ultimately determined by ionic charge on the casein molecules (electrostatic repulsion), hydrophobicity of the casein, hydration of the casein (due to ionization of the casein), bound calcium phosphate, temperature, and proteolysis (Roefs et al., 1990). These are strongly influenced by the rate and extent of acid development (pH) at each step in the manufacturing process and ionic strength of the serum phase (mostly sodium chloride and ionic calcium). Of particular importance are the pH at rennet addition, whey separation, and the lowest pH obtained in the cheese. The lower the pH at the time of rennet coagulation or the lower the pH of the cheese, the less bound calcium and (to a point) greater casein hydration. It follows that the higher the moisture and lower the bound calcium, the softer the cheese and to a point, the greater the melt (Kellar et al., 1974). If the pH is lowered to <5.0 or the cheese is heated, the casein molecules do not associate as much with the water and begin to rearrange into large aggregates with free serum forming between the casein aggregates. The casein molecules within the aggregates interact more closely, but the interaction between aggregates is less. The cheese becomes brittle (grainy) but less chewy, there is a loss of stretch, and there is an increase in the release of fat and serum if the cheese is warmed. To overcome the problem of excessive firmness and poor melt properties often associated with a reducedfat cheese, manufacturing protocols must be adjusted (usually to obtain a lower final cheese pH, or lower pH at rennet addition) to obtain the appropriate level of bound calcium, casein hydration, and proteolysis. These adjustments, coupled with manufacturing practices that increase moisture content, are being used commercially to produce reduced-fat and light cheeses that are similar in melt, firmness, chewiness, and texture to higher fat varieties. Conversely most body and performance defects often associated with reduced-fat cheeses are due to inappropriate manufacturing protocol.
1027
1028
JOHNSON ET AL.
To attain a higher moisture cheese, the cheese-making protocol is adjusted to restrict syneresis. An effective method of increasing cheese moisture involves rinsing the curd with water that is lower in temperature than the curd. Cold curd (cheese) will hold water. The water is eventually absorbed by the cheese casein network under suitable conditions. These conditions are governed by the charge on the casein molecules (loss of calcium), pH, ionic strength, and temperature (van Vliet and Walstra, 1994). While rinsing initially improves the physical properties of reduced-fat cheeses, it may produce a cheese that lacks Cheddar flavor, and the cheese may develop a weaker, pasty body during aging (Johnson and Chen, 1995). Other manufacturing methods used to increase cheese moisture include incorporation of denatured serum proteins (high milk heat treatment, use of concentrated milks, whey protein concentrate added directly or via starter media, addition of starch or other fat mimetics), firmer coagulum at cutting, lower pH at rennet addition, larger curd particle size at cutting, less stir-out after cutting, reduced acid development during stir-out, less stir-out time after whey and curd separation, and lower cook temperatures. More recent techniques include homogenization of the cream (Metzger and Mistry, 1994) and use of exopolysaccharide-producing bacteria (Low et al., 1998). Aleandri et al. (1989) found that an increase in curd firmness at cutting increased cheese yield (increased moisture) but lowered fat recovery. Several other research groups evaluated the effect of milk coagulum firmness at cutting in full fat Cheddar cheese. Results were varied. Mayes and Sutherland (1989) found that cheese moisture increased when the coagulum for Cheddar cheese was cut at 200% of the control setting time. However, Bynum and Olson (1982) found no significant differences in cheese moisture after milk coagulum setting times were increased from 28 to 47 min. Banks and Muir (1984) concluded that the firmness of renneted gels at cutting was not directly related to cheese yield or process efficiency. Others (Mayes and Sutherland, 1989; Riddel-Lawrence and Hicks, 1989) demonstrated that after cutting the coagulum, a healing time before agitation influenced cheese moisture and yield more than did milk gel firmness at cutting. Johnston et al. (1991) showed that a combination of speed and duration of cutting and the subsequent speed of stirring prior to cooking can influence fat recovery and curd fines. Thus, some of the discrepancy between published reports may be due to manufacturing practices after the curd is cut. The expected difference in moisture retention in a cheese that is produced from a soft coagulum versus a firm coagulum at cutting would be less in a full fat Cheddar cheese than in a lower fat Cheddar Journal of Dairy Science Vol. 84, No. 5, 2001
cheese. One reason for this is the physical characteristics of the clot (Lagoueyte et al., 1994; Zoon et al., 1988a, 1988b) and curd. In addition, small differences may not be found to be statistically significantly different if the variation between trials is large. During coagulation, casein micelles first form chains, then small aggregates, and then larger aggregates (Roefs et al., 1990). The space (pores) between the aggregates is filled with fat and serum. The more fat globules, the greater the space between casein aggregates. As the clotting process continues, individual groups of aggregates become larger, serum is forced out of the aggregates, and the coagulum becomes firmer. The space between aggregates concomitantly increases in size, further limiting the contact between aggregates. If the coagulum is cut soft, the potential for the aggregates to react with each other is greater than if the coagulum is cut firm due to the proximity of the aggregates. Fat at the surface of the curd particle is lost upon agitation. With the loss of fat and with the pressure exerted on the curd during stirring, there is a collapse of the pore allowing for an increase in reaction between aggregates. In turn, syneresis is increased, and a “skin” is formed on the outside of the curd particle. Until the skin is formed, fat within the pore can be lost to the whey, and the curd particle is more susceptible to the rigors of agitation. The curd is more brittle and breaks apart more readily. Consequently, a coagulum that is cut soft will lose less fat and serum than a coagulum that is cut firm if sufficient time is allowed for formation of the skin. The amount of fat and casein loss is dependent on the cutting mechanism. Higher losses occur with manual cutting than with mechanical cutting (Johnston et al., 1991). If the soft coagulum is agitated before the skin develops, the curd will break up, leading to more curd fines and greater fat loss. With an increase in curd fines, more nitrogen is lost to the whey. As the casein content in the milk increases, the coagulum forms faster and subsequently will be firmer than lower casein milks if the temperature, calcium ion activity, time, and pH of coagulation are the same (Green and Grandison, 1993). Indeed, to slow the rate of aggregation, concentrated milks (higher in casein) can be set at lower temperatures. After the whey is separated from the curd, it is either continually stirred (stirred curd Cheddar process) or allowed to mat (milled curd Cheddar). In stirred curd Cheddar, the longer the curd is stirred the greater the moisture loss. If the curd is allowed to mat, it will retain more moisture, but serum and fat are lost after milling as new surface area is exposed. Subsequent salting and stirring of the milled curd exacerbates the moisture and fat loss. This paper will focus on the use of increased coagulum firmness at cutting as a method to increase
RENNET COAGULATION TIME AND CHEESE YIELD Table 1. Cheese manufacturing protocol for 50% reduced-fat Cheddar cheese. Rennet coagulation time (min)1 25
48
65
pH
Total elapsed time Initial milk Add starter Add coagulant Cut Drain Mill Add salt
43 68 103 201 219
0 ± ± ± ± ±
5 1 6 14 14
0 20 ± 68 ± 102 ± 196 ± 214 ±
2 7 8 6 7
0 5 ± 70 ± 107 ± 199 ± 217 ±
0 4 5 8 6
6.61 6.56 6.54 6.50 6.36 5.91 5.82
± ± ± ± ± ± ±
0.03 0.03 0.03 0.03 0.02 0.01 0.04
Coagulation time = Addition of coagulant to cut.
1
moisture content in reduced-fat Cheddar cheese. The effect of coagulum firmness on fat and nitrogen retention in whey, pressed whey, and cheese is also determined. MATERIALS AND METHODS Cheese Manufacturing Table 1 contains an outline of the cheese manufacturing schedule. A licensed Wisconsin cheese maker manufactured the cheese in the University of Wisconsin dairy processing pilot plant. Raw whole milk was skimmed to approximately 1.3% fat, pasteurized at 73°C for 16 s, and stored overnight at 3°C. The next morning, 249.7kg portions of milk were heated to 43°C; the milk was then cooled to a ripening temperature of 32°C. A single strain of Lactococcus lactis ssp. cremoris (D11; RhoˆnePoulenc, Madison, WI) grown in LF media (RhoˆnePoulenc), held overnight at 7°C, pH 4.40, was inoculated into cheese milk at a rate of 1.25% (wt/wt). This is a slow acid-producing culture. We hoped this would minimize any pH differences during variations in the time of rennet coagulation. Five minutes before the addition of the milk coagulant, 49 ml of calcium chloride (32% solution; Rhoˆne-Poulenc) was added. Doublestrength chymosin (Chymax, Pfizer, Milwaukee, WI) was added at the rate of 19 ml per 250 kg of milk. The time from adding the starter to rennet addition was varied to ensure that all treatments were cut, drained, milled, and salted at the same time and curd pH. An experienced licensed cheese maker subjectively evaluated the firmness level of the coagulum at cutting. The cheese maker did not cut by time but by his evaluation of the coagulum firmness. It coincidentally turned out that there was little variation in actual cutting time. The cheese maker was unaware of the time until the curd was cut. The coagulum was cut with 0.95-cm knives at a pH of 6.5, and the curd was given a 5-min healing time, followed by 10 min of gentle agitation
1029
before heating started. The temperature of the curdwhey slurry was raised from 32 to 38°C over 25 min. After reaching cooking temperature, the whey was slowly drained. Cheese slabs were cheddared, piled two high, and then milled at a curd pH of 5.9. Fifteen minutes after milling, curd was salted at a rate of 2.50 g of flake salt/kg of milk. Curd was packed into 9-kg Wilsonstyle hoops and pressed for 4 h at ambient temperature. Cheddar blocks were weighed, vacuum-packaged, and aged at 7°C. Analysis All compositional tests were in duplicate. Whey samples were collected 5 min after the start of draining. Press whey samples were a composite of whey collected from milling through pressing of the cheese. Milk, whey, and press whey samples were analyzed for fat by Mojonnier (Marshall, 1992) protein (total percentage of N × 6.38) by Kjeldahl (AOAC, 1995), and casein by the International Dairy Federation procedure (IDF, 1964). Milk was also tested for NPN by weighing a 15-g sample and mixing it with 5 g of 48% TCA. After 30 min at 25°C, the mixture was filtered (Whatman no. 1 filter paper; Whatman Corp., Clifton, NJ). The clear filtrate was weighed, and protein (percentage of N × 6.38) was determined by Kjeldahl (AOAC, 1995). Cheeses were sampled by removing a 2-cm slab of cheese from the end of the block, and then cutting another 1-cm slab of cheese from the block for analysis. Cheese was analyzed for moisture by vacuum oven (Vanderwarn, 1989), fat by Babcock (Marshall, 1992), pH by the quinhydrone method (Van Slyke and Price, 1979), salt by chloride electrode (model 926; Corning Glass Works, Medfield, MA; Johnson and Olson, 1985), and protein by Kjeldahl (AOAC, 1995). Cheese Yield Calculations Milk was weighed to ±0.1 kg (model 31-1822-FD; Toledo Scale Company, Toledo, OH), press whey was weighed to ±0.001 kg (Mettler PJ6; Mettler Instrument Corp., Highstown, NJ), and cheese was weighed to ±0.045 kg (model 2071; Toledo Scale Company). The weight of the whey was calculated by subtracting the weight of the cheese and press whey from the weight of the milk. The percentage of fat or N recovered in the cheese was the total amount of fat or N in the cheese divided by the total amount of fat or N in the milk. Sensory Evaluation Descriptive taste panels consisted of six to 10 experienced judges who evaluated the cheese for flavor and Journal of Dairy Science Vol. 84, No. 5, 2001
1030
JOHNSON ET AL.
Table 2. Average milk composition used for the manufacture of 50% reduced-fat Cheddar cheese. Analysis % Milk fat Total solids Total protein1 % NPN True protein2 % NCN Casein3 C:F ratio
1.285 10.12 3.243 0.035 3.018 0.115 2.512 1.955
± ± ± ± ± ± ± ±
0.033 0.07 0.043 0.002 0.037 0.002 0.047 0.065
Total % Nitrogen × 6.38. (Total % Nitrogen − % NPN) × 6.38 3 (Total % Nitrogen − % NCN) × 6.38
making day and time from rennet addition to cutting the coagulum. Cheese-making day reflected differences, mainly due to variation in milk composition. Standard error of the means was derived from the error mean square term of the ANOVA. A Fisher’s protected least significant difference was calculated to evaluate differences between treatment means when P < 0.05. Sensory data was analyzed using the SAS PROC GLM method (1990).
1
RESULTS
2
Cheese Manufacturing
body characteristics using category scaling. Judges evaluated the following flavor attributes: Cheddar flavor intensity (1 = none to 7 = aged), acid flavor intensity (1 = flat to 7 = pronounced), and intensity of bitterness and off-flavors (1 = none to 7 = pronounced). Body analysis included: body (1 = very soft to 7 = very firm), and smoothness (1 = very curdy to 7 = very smooth). The taste panelists first scored the control cheese (rennet coagulation time of 23 min), and gave it a consensus rating in all categories. Random numbers were assigned to the cheeses, including the control cheeses. Judges scored cheese attributes using the reference (consensus) as a guide. Experimental Design and Statistical Analysis On a single cheese-making day, three vats of reducedfat Cheddar cheese were manufactured using one lot of milk split into three portions. On each day, each of the different coagulum firmness levels were tested. The firmness level was a subjective evaluation by an experienced licensed cheese maker. The cheese maker did not cut by time and was unaware of the time until the curd was cut. Cheese making was replicated on eight separate days for a total of 24 vats of cheese. Statistical analysis for cheese composition and cheese yield were completed by the statistical method described by Emmons and Binns (1990) using the SAS system (1990). The independent variables in the model were cheese-
Total cheese-making time for all vats from starter addition to salting was completed in approximately 3 h and 35 min (Table 1). The slow rate of acid development by the starter ensured that all treatments were cut, drained, milled, and salted at approximately the same time and curd pH. Milk, Whey, and Cheese Composition Milk composition is shown in Table 2. Table 3 presents composition of whey and press whey. Percentages of nitrogen in whey and in press whey did not differ as a result of the rennet coagulation time. Significant differences were noted in the percentages of fat in the whey and press whey. Cheese composition as analyzed from samples collected at 3 d is given in Table 4. Moisture increased as the rennet coagulation time increased (P < 0.05) Subsequently, cheese fat, protein, and salt contents in the cheese also differed (P < 0.05). After 2 wk of aging, the control cheeses were higher in pH than cheeses with the higher moisture content (Table 5). Fat and Protein Recovery Table 4 presents actual weights (milk, cheese, and press whey), calculated weights (whey weight is milk weight minus cheese weight and weight of press whey), and percentages of fat and N recoveries. The rennet coagulation time directly affected the rate at which whey was expelled from the curd, as shown by differ-
Table 3. Composition of whey and pressed whey collected during manufacture of reduced-fat Cheddar cheese Rennet coagulation time
Whey % Fat
% Nitrogen
% Fat
% Nitrogen
25 min 48 min 65 min
0.156 ± 0.008 0.160b ± 0.014 0.175a ± 0.015
0.142 ± 0.005 0.141a ± 0.007 0.140a ± 0.008
0.386 ± 0.028 0.349b ± 0.026 0.343b ± 0.036
0.143a ± 0.009 0.140a ± 0.007 0.145a ± 0.008
b
Pressed whey
a
a
Means in the same row having different superscripts are significantly different (P < 0.05).
a,b
Journal of Dairy Science Vol. 84, No. 5, 2001
1031
RENNET COAGULATION TIME AND CHEESE YIELD Table 4. Average composition, fat, and nitrogen recovery for 50% reduced-fat Cheddar cheese. Rennet coagulation time (min) 25 % % % % %
Moisture Fat Protein1 Salt FDM
46.44 14.68 32.08 1.77 27.41
% Fat recovery, cheese % Fat recovery, whey % Fat recovery, pressed whey % Fat recovery, total % Nitrogen recovery, cheese % Nitrogen recovery, whey % Nitrogen recovery, pressed whey % Nitrogen recovery, total Whey weight (kg)2 Pressed whey weight (kg) Total yield (kg)
48 ± ± ± ± ±
0.98a 0.42a 0.68a 0.06a 0.72a
48.29 14.18 31.04 1.75 27.41
65 ± ± ± ± ±
0.80b 0.44b 0.80b 0.10a 0.56a
48.90 13.86 30.92 1.61 27.11
± ± ± ± ±
1.17c 0.56c 0.75b 0.15b 0.61b
88.1 ± 0.7a 11.1 ± 0.5a
87.7 ± 1.0a 11.2 ± 0.8a
86.4 ± 1.3b 12.2 ± 0.9b
0.5 ± 0.1a 99.6 ± 0.9
0.6 ± 0.2a 99.5 ± 1.0
0.8 ± 0.2b 99.3 ± 1.0
74.6 ± 0.9a 25.2 ± 0.7a
74.4 ± 1.0a 24.7 ± 1.0a
74.3 ± 1.6a 24.8 ± 1.0a
0.4 ± 0.0a 100.3 ± 0.9
0.6 ± 0.2b 99.7 ± 0.6
0.8 ± 0.1c 99.9 ± 1.0
229.79 ± 0.67a 4.02 ± 0.48a 19.42 ± 0.27a
227.58 ± 1.36b 5.63 ± 1.35b 20.04 ± 0.41b
225.92 ± 1.65c 7.10 ± 1.26c 20.19 ± 0.52b
Means in the same row having different superscripts are significantly different (P < 0.05). % Total nitrogen × 6.38. 2 Whey = (milk + starter − cheese + salt − pressed whey) Milk + starter weight was a constant at 252.90kg. a,b,c 1
ences in the mean weights of the whey and press whey. As the rennet coagulation time increased, there was a decrease in the amount of whey collected before milling and an increase in the amount of whey collected after milling and pressing. However, the slight increase in volume of whey expelled during pressing would result in a slight increase in the loss of fat, nitrogen, and salt. The total percentages of fat and N recovered did not differ. A greater (P < 0.05) percentage of fat was recovered in the whey and press whey, and less fat was recovered in the cheese when the milk had a rennet coagulation time of 65 min. There were no differences in fat recovery in cheese, whey, or press whey between milks with a rennet coagulation time of 25 or 48 min. The percentage of N recovered in cheese tended to decrease with increasing coagulum firmness at cutting, but the difference was not statistically significant. There were greater N losses in the press whey, with an increase in coagulum firmness at cutting. This is
Tablel 5. Cheese pH during 26 wk for 50% reduced-fat Cheddar cheese. Rennet coagulation time (min)
Cheese age (wk) 0.5
2
6
13
26
25 48 65
5.39 5.33 5.28
5.19 5.10 5.04
5.21 5.05 5.04
5.18 5.04 5.00
5.20 5.08 5.07
due to the larger volumes of whey expelled after milling. However, the sum of N recovered in the whey and press whey did not differ among treatments.
Cheese Yield There was an increase in cheese yield as the coagulum firmness increased. The increase was due to an increase in the moisture content of cheese. The additional serum solids that would accompany the increase in moisture would also contribute to an increase in cheese yield, albeit too small to measure at the small difference in moisture observed in our experiments.
Sensory Evaluation Table 6 contains the results of the descriptive taste panels at 3 and 6 mo. Rennet coagulation time did not affect Cheddar flavor intensity throughout aging. However, judges noted an increase in the acid flavor intensity and smoothness (less curdy) and a decrease in firmness in cheeses made from milk with a rennet coagulation time longer than 25 min. Although the cheeses made from milk with a rennet coagulation time of 65 min developed more bitterness and off-flavor intensity at 6 mo than did the other cheeses, the intensity of these flavors would be described as very slight to slight. Journal of Dairy Science Vol. 84, No. 5, 2001
1032
JOHNSON ET AL. Table 6. Descriptive taste panel results for 50% reduced-fat Cheddar cheese cut at different milk coagulum firmness at 3 and 6 mo of aging. Sixteen panels were conducted, each consisting of 6 to 10 experienced judges. Data are the means of the 8 taste panels conducted at each age. Rennet coagulation time Cheese at 3 mo of age 25 48 65 Cheese at 6 mo of age 25 48 65
Cheddar flavor intensity1
Acid flavor intensity2
Bitter flavor intensity3
Off-flavor intensity3
Body4
Smoothness5
2.4a 2.5a 2.5a
3.1a 3.5b 3.8c
1.7a 1.7a 1.9a
2.4a,b 2.3b 2.8a
5.2a 4.0b 3.7b
2.7a 3.7b 4.0b
3.2a 3.5a 3.4a
3.5a 3.8a 4.0a
2.3a 2.3a 2.6b
2.8a 3.0a 3.2b
4.4a 3.8b 4.0b
3.8a 4.5b 4.3b
Means in the same column having different superscripts are significantly different (P < 0.05). Cheddar flavor intensity: 2 = very mild, 3 = mild, and 4 = mild to medium. 2 Acid flavor intensity: 3 = ideal acid, and 4 = slight acid. 3 Bitter and off-flavor intensity: 1 = none, 2 = very slight, 3 = slight, and 4 = slight to definite. 4 Body: 3 = slight soft, 4 = neither soft nor firm, and 5 = slight firm. 5 Smoothness: 3 = slight curdy, 4 = neither curdy nor smooth, and 5 = slight smooth. a,b,c 1
DISCUSSION Cheese Moisture and Fat Recovery As expected, increasing the coagulum firmness at cutting significantly increased cheese moisture and cheese yield. However, it also resulted in more fat lost to the whey during manufacture. These results can be attributed to the rigidity and structure (pore and casein aggregate size) of the network (Lagoueyte et al., 1994). Milling the curd increases the surface area of the slabs of cheddared curd. Fat is released from the newly exposed surface. It follows that a more porous curd (as the result of a more rigid coagulum) will release more fat, serum, and whey upon subsequent pressing than a curd produced from a coagulum that was softer when cut. In our experiments, the time from cutting the coagulum to putting the salted curd into hoops for pressing was the same for all cheeses. We also used the milled curd method of making Cheddar cheese. If we had used a stirred curd method of making Cheddar cheese, the differences in moisture between the cheeses may not have been as noticeable. The stirred curd process (or dry stir-out) is often used to reduce moisture in cheese as it exposes more surface area to evaporation. In addition, the weight of the curds on each other helps to collapse the space between aggregates of micelles and results in loss of serum from the curd particle. Serum lost from individual curd particles (via syneresis) is more easily drained from the curd and is not trapped within a mass of curd as in the cheddaring process. Sensory Attributes As anticipated, the increased moisture content resulted in a softer, smoother Cheddar cheese. The effect Journal of Dairy Science Vol. 84, No. 5, 2001
is not due to an increase in moisture per se, but to an increase in casein hydration. Higher cheese moisture will result in more sugar in the curd, which in turn will lead to more acid development (more acid tasting cheese). This leads to a slightly lower cheese pH, and a decrease in bound calcium. Subsequently, an increase in casein hydration occurs, and an increase in casein mobility (able to rearrange) and a less curdy cheese. A more hydrated casein is also more prone to proteolysis. In addition, the residual chymosin would be more active at the lower pH. Increased chymosin activity would lead to a softer cheese but may increase bitterness. CONCLUSION Our results are consistent with the model described in the introduction. As this model predicted, increasing the curd firmness as cutting (increased rennet coagulation time) increased moisture content of the cheese but decreased fat recovery. In addition, there was more whey and fat lost at pressing, with increasing curd firmness at cutting. The increase in moisture offset the decrease in fat recovery resulting in higher cheese yields. In our method of cheese manufacture, the stirout time is minimized and the curd is cheddared not stirred. Stirred-curd cheese may be lower in moisture than cheddared cheese. This depends on the duration of stirring of the curd after whey drainage. The increased moisture and physico-chemical changes that occur to the casein (due to a decrease in pH), undoubtedly resulted in a more acid, less firm, and smoother cheese. There will be a limit to the amount of increase in moisture obtained through increasing the rennet coagulation time. There will also be a point at which increasing coagulum firmness at cutting will not result in an in-
RENNET COAGULATION TIME AND CHEESE YIELD
crease in moisture in cheese. In addition, unless other manufacturing steps are not carefully controlled, the increase in moisture obtained through cutting at a firmer coagulum will be negated. We have observed that incorporation of a cold-water rinse is more effective at increasing moisture content of the cheese than is increasing the firmness of the coagulum at cutting. The protocol that we used to make reduced-fat Cheddar did not include any means to reduce the lactose content of the cheese, i.e., whey dilution or curd rinsing. A higher pH at coagulant addition, draining, milling, and salting (than in a typical Cheddar manufacturing protocol), will keep an important buffering compound in the cheese (calcium phosphate), and it will not be lost in the whey. In addition, the phosphoserine in the casein remains unprotonated or associated with calcium phosphate and maintains its buffer potential. Calcium phosphate is released from the casein (phosphoserine) as the pH is lowered. This results in the retention of calcium phosphate in the cheese. Therefore even though there is far more acid in the cheese, there is also more buffering capacity. The phosphate becomes protonated, and at pH above 5.0 the casein will become more hydrated and softer. In addition the casein will be more prone to proteolysis resulting in a softer cheese. ACKNOWLEDGMENTS The authors thank Sonia Cotto-Febo, Amy Dikkeboom, Ann Kieslich, Al Muelling, Ellen Shumaker, and Chris Simon for their assistance and support in cheese making and analytical work. Authors are also appreciative of Bill Klein and other workers in the University of Wisconsin-Madison Dairy Plant for milk processing. The Wisconsin Center for Dairy Research and the National Dairy Promotion and Research Board funded this project. REFERENCES Aleandri, R., J. C. Schneider, and L. G. Buttazzoni. 1989. Evaluation of milk for cheese production based on formagraph measures. J. Dairy Sci. 72:1967–1975. Association of Official Analytical Chemists. 1995. Official Methods of Analysis. 16th ed. AOAC, Arlington, VA. Banks, J. M., and D. D. Muir. 1984. Coagulum strength and cheese yield. Dairy Ind. Int. 39:17,19,21,36. Bynum, D. G., and N. F. Olson. 1982. Influence of curd firmness at cutting on Cheddar cheese yield and recovery of milk constituents. J. Dairy Sci. 65:2281–2290. Emmons, D. B., and M. Binns. 1990. Cheese yield experiments and proteolysis by milk-clotting enzymes. J. Dairy Sci.73:2028–2043.
1033
Green M. L., and A. S. Grandison. 1993. Secondary (non-enzymatic) phase of rennet coagulation and post-coagulation phenomena. Pages 101–140 in Cheese: Chemistry, Physics, and Microbiology. P. F. Fox ed. Chapman and Hall, London, UK. International Dairy Federation. 1964. Determination of the casein content of milk. Int. Dairy Fed. Standard 29. Int. Dairy Fed., Brussels, Belgium. Johnson, M. E., and C. M. Chen. 1995. Technology of manufacturing reduced-fat Cheddar cheese. Pages 331–337 in Chemistry of Structure-Function Relationships in Cheese. E. L. Malin and M. H. Tunick, ed. Plenum Press, New York. Johnson, M. E., and N. F. Olson. 1985. A comparison of available methods for determining salt levels in cheese. J. Dairy Sci. 68:1020–1024. Johnston, K. A., F. P. Dunlap, and M. F. Lawson. 1991. Effects of speed and duration of cutting in mechanized Cheddar cheesemaking on curd particle size and yield. J. Dairy Res. 58:345:354. Kellar, B., N. F. Olson, and T. Richardson. 1974. Mineral retention and rheological properties of Mozzarella cheese made by direct acidification. J. Dairy Sci. 57:174–180. Lagoueyte, N., J. Lablee, A. Lagaude, and B. Tarodo de la Fuente. 1994. Temperature affects microstructure of renneted milk gel. J. Food Sci. 59:956–959. Low, D., J. A. Ahlgreen, D. Horne, D. J. McMahon, D. J. Oberg, and J. F. Broadbent. 1998. Influence of Streptococcus thermophilus MC-1C capsular exopolysaccharide on cheese moisture levels. Appl. Environ. Microbiol. 64:2147–2151. Marshall, R. T., ed. 1992. Standard Methods for the Examination of Dairy Products. 16 th ed. Am. Publ. Health Assoc., Inc. Washington, D. C. Mayes, J. J., and B. J. Sutherland. 1984. Coagulum firmness and yield in Cheddar cheese manufacture—the role of the curd firmness instrument in determining cutting time. Aust. J. Dairy Technol. 39:69–73. Mayes, J. J., and B. J. Sutherland. 1989. Further notes on coagulum firmness and yield in Cheddar cheese manufacture. Aust. J. Dairy Technol. 44:47–48. Metzger, L. E., and V. V. Mistry. 1994. A new approach using homogenization of cream in the manufacture of reduced fat Cheddar cheese. Manufacture, composition, and yield. J. Dairy Sci. 77:3506–3515. Prentice, J. H., K. R. Langley, and R. J. Marshall. 1993. Cheese rheology, Pages 303–340 in Cheese: Chemistry, Physics, and Microbiology. P. F. Fox ed. Chapman and Hall, London, UK. Roefs, S.P.F.M., T. van Vliet, H.J.C.M. van den Bijgaart, A.E.A. de Groot-Mostert, and P. Walstra. 1990. Structure of casein gels made by combined acidification and rennet action. Neth. Milk Dairy J. 44:159–188. Riddel-Lawrence, S., and C. L. Hicks. 1989. Effect of curd firmness on stirred curd cheese yield. J. Dairy Sci. 72:313–321. SAS User’s Guide: Statistics, Version 6.0 Edition. 1990. SAS Inst., Inc., Cary, NC. Vanderwarn, M. A. 1989. M.S. Thesis. Analysis of cheese and cheese products for moisture. University of Wisconsin, Madison Van Slyke, L. L., and W.V. Price. 1979. Cheese. Ridgeview Publ. Co., Atascadara, CA. van Vliet, T., and P. Walstra. 1994. Water in casein gels; how to get it out or keep it in. J. Food Enginering. 22:75–88. Zoon, P., T. van Vliet, and P. Walstra. 1988a. Rheological properties of rennet-induced skim milk gels. 1. Introduction. Neth. Milk Dairy J. 42:249–269. Zoon, P., T.van Vliet, and P. Walstra. 1988b. Rheological properties of rennet-induced skim milk gels. 2. The effect of temperature. Neth. Milk Dairy J. 42:271–294
Journal of Dairy Science Vol. 84, No. 5, 2001