- Email: [email protected]
A Computerized Curd Firmness Meter1
A Computerized Curd Firmness Meter1 D. A. MACKIE,2 D. W. HAGBORG,3 D. C. BECKElT,2 and D. B. EMMONS2 AgriculbJre Canada Central Expertment Farm Ottawa, Ontario, Canada K1A OC6
ABSTRACT
The curd fIrmness meter was inter faced with an Apple IIe computer to in crease both the efficiency of the instru ment and the accuracy of the instrumental measurements. The computerization al lows for collection of real-time data, graphical analysis, and maintenance of results in a data base capable of generat ing reports. The newly modified curd firmness meter can measure the firmness of cheeses and gels. The mean, lowest, and highest firmness points are obtained from the computer-generated. force-time curve. The mean firmness values distin guish among samples, and the low and high firmness points give information on variability within samples. (Key words: curd firmness, computerized meter, cheese) INTRODUCTION
Several modifications of the Cherry-Burrell curd-tension meter have taken place over the last 30 yr. Each change has improved both the accuracy and efficiency of the instrument. In 1955, Irvine (3) modified the meter to measure the resistance to passage of a wire through a block of Cheddar cheese. Emmons and Price (2) made a further adaptation to allow the measurement of cottage cheese curd firmness. The instrumentally measured resistance was found to be directly related to the fIrmness of the curd as determined by a sensory panel for both Cheddar and cottage cheese. The curd firmness meter can also be used to measure gel firmness in products such as yogurts, puddings, and sour cream.
Received September 25, 1989. Accepted January 11, 1990. Ipood Research Centre Contribution Number 828. 2pood Research Centre Building 55. 3Systems and Consulting Division, Carling Building. 1990 J Dairy Sci 73:1648-1652
~ 1966, modifications were implemented by ':'Olsey and Emmons (4) to increase the preci s10n of measurement and to provide a perma nent record of each measurement on a strip chart. The three major changes were: 1) the dietetic scale was replaced with a strain-gauge transducer coupled to an amplifier and strip chart recorder, 2) the length of the cutting edge was increased from one wire to three parallel wires, and 3) the drive mechanism was changed from a gear-drive to a screw-drive. This paper describes a fuither modification, which increases the efficiency of the instrument (less time to obtain results) and the accuracy of results by interfacing the curd firmness meter with an Apple He computer. The reader is referred to the Voisey and Emmons (4) and Emmons et al. (1) papers for a complete de scription and detailed illustrations of the ten sion or curd firmness meter. A brief description of the apparatus will be repeated in this paper to help the reader understand the basic princi ples in instrumental curd firmness measure ment.
INSTRUMENTATION
When measuring the firmness of a cheese, the sample is placed into a slotted aluminum cylindrical container (Figure 1). Three parallel wires held in a circular frame pass through the slotted container at a rate of .29 crn/s. When measuring the firmness of a gel, the sample is p~sented to the meter in any appropriate con tamer, such as a beaker, cup, or bowl (Figure 2). Two concentric circular knives cut through the gel at a rate of .29 crn/s. The force applied by either the cutting wires or knives is trans ferred to a strain-gauge transducer and produces an output voltage which is proportional to the force applied. This output voltage is amplified and the signal is recorded. The newly modified curd firmness meter is interfaced to a computer (Figure 3), which re places the strip-chart recorder previously used. The computerization enables users to collect
1648
OUR INDUSTRY TODAY
Figure I. Slotted aluminum container and 3 cutting wires for cheese firmness measurement.
data on a real-time basis from the strain-gauge, perfonn automatic graphical analysis of the data, and maintain the results in a data base capable of generating reports. The system is based on an Apple lIe with 64 K random access memory (RAM) running DOS 3.3 from a 128-K system software disk drive and a 128-K data disk drive or a hard disk. The analysis program runs in compiled BASIC (Ap plesoft BASIC) together with a utility which automatically relocates DOS to the upper 13K of RAM. Other components include an Interac tive Structures AID conversion card, a Moun tain Hardware clock, and a printer capable of graphics and compatible with Mannesman Tally or Epson graphics. DATA COLLECTION AND ANALYSIS
To use the curd finnness meter, the instru ment (strain-gauge) is ftrst calibrated with a
1649
Figure 2. Circular knives for gel firmness measurement.
known laboratory weight. An idea of the ap proximate firmness of the sample to be tested is beneficial in choosing the appropriate calibra tion weight. The ideal calibration weight should be 25 to 33% of the expected maximum force. After the calibration is complete, the calibration curve results are automatically printed, and the user returns to the main data collection menu. To begin data collection, a file name is entered for the test sample. The sample-filled container is then placed on the strain-gauge, the weight of the cheese and container are tared, and the wires or knives start their downward stroke. For a solid cheese, such as Cheddar, a block is cut to just fit inside the cylinder (5.5 cm in diameter, 8.5 cm in height). For cottage cheese, approximately ZOO g of sample are spooned into the cylinder. The cottage cheese is packed finnly after each spoonful to minimize pockets of air or liquid between the curd parti cles. A 2-kg cylindrical weight is placed on the Journal of Dairy Science Vol. 73,
No.6, 1990
1650
MACKIE ET AL.
Figure 3. 1be curd firmness meter interfaced with an Apple ITe computer.
curd for approximately lOs to pack the curd unifonnly. A plastic sleeve is placed around the container during this pressing stage to prevent the escape of curds through the slots in the container. The amount of gel sample depends on the diameter and height of the container used. All samples are kept at 5°e until the firmness measmement is taken. During the curd firmness measmement, the force required for the wires or knives to cut through the sample is recorded as a function of time (Figures 4 and 5). The force builds up from zero (point A) as the sample compresses under the load The wires or knives eventually cut into the sample, after which the force re corded will fluctuate as the wires pass through the sample to point B, the bottom of the stroke. The user can continue data collection on subsequent samples or proceed to the data anal ysis function. There is a choice of two types of curve analysis: Cheddar (solid) cheese or cot tage cheese. With the Cheddar cheese curve analysis, a vertical line is drawn from the 2.5-s time point upward to intersect (0) with the test sample curve (Figure 4). The values are calculated from the curve after this intersection point. The 2.5-s time point ensures the cutting head has penetrated the sample sufficiently. The Cheddar cheese analysis is also used for gel firmness analysis. With the cottage cheese Journal of Dairy Science Vol. 73,
No.6, 1990
...
F
~
E
...~
C
TIME (sl
Figure 4. Typical computer-generated, force-time curve for solid cheese or gels. A is the point at which the wires make contact with the cheese sample, B is the point of completion of the downward stroke of the wires through the cheese sample, C is the lowest fumness point, D is the curve intersection point where the curve analysis begins, E is the mean firmness, and F is the highest flmllless point
curve analysis (Figme 5), a horizontal line is drawn from the lowest fluctuation (C) to inter sect with the initial vertical rise in force (0). A vertical line is then drawn through the point of intersection and all values are calculated from that point. Although this intersection point (0) may actually be before complete insertion of the cutting head into the sample has taken place, this analysis allows for all the variation in finnness of the individual cottage cheese curds to be incorporated into the calculation of the mean firmness. The same information is obtained from both analyses: mean force (E), low point (C), and high point (F). The analyzed results are printed along with the curve and include filename as signed to the test sample, mean force (g), low point (g), high point (g), calibration factor, test date, analysis type (cottage or Cheddar), along with other program parameters. The computer generated results eliminate any inaccuracies previously possible when visually extracting the firmness points from the strip chart recorder graph.
1651
OUR INDUSTRY TODAY
TABLE 1. Means,l standard deviations, and coefficients of variation (%) for low point, mean, and high point curd firmness measurement.
B w
E
1i! c o u.
Brand
Firmness (g/cm wire)
A
B
C
D
Low point SD CV
21.7 2.84 13.1
21.1 1.29 6.1
16.5 2.84 17.2
Mean SD CV
26.6 1.92 7.2
24.2 .71 3.0
19.5 2.76 14.2
15.6 .82 5.2 18.6 .63 3.4
High point SD CV
33.0 2.18 6.6
27.7 1.31 4.7
23.1 2.89 12.5
21.6 1.05 4.9
IMeans of 10 measuremenrs.
TIME (s)
Figure 5. Typical computer generated, foree-time curve for cottage cheese. A is the point at which the wires make contact with the cheese sample, B is the point of comple tion of the downward stroke of the wires through the cheese sample, C is the lowest firmness point, D is the curve intersection point where the curve analysis begins, E' is the mean fumness, and F is the highest firmness point.
EXPERIMENTAL EXAMPLE
To highlight the usefulness of the infonna tion that can be obtained from this computer ized curd finnness meter, demonstrative results from a study conducted at the Food Research Centre, Agriculture Canada, Ottawa, on cottage cheese are presented and discussed. Five con tainers of each of four commercially available brands of 2% milk fat (500 ml) creamed cot tage cheese were purchased. All five containers for each brand were from the same production lot, and the closest "best before dates" were purchased among brands. Samples were kept at SoC until evaluation. Two instrumental curd finnness measurements were taken from each container for a total of 10 finnness measure ments per brand. There was a difference among the cheeses (Table 1) for mean, low point, and high point finnness. Brand A was the most firm, and brands C and D were the least firm. Attention should be drawn to the standard deviations and coefficients of variation. There was more varia-
tion in firmness of brand C than the other brands, except for the low point measurement for brand A From the computer printout, the individual measured points can be examined for each test sample. For example, brand C had a range in low point measurement from 12.5 to 22.8 g/cm wire, in the high point measurement from 19.0 to 29.1 g/cm wire, and in mean firmness estimation from IS.9 to 25.8 g/cm wire. In comparison, the ranges in low point, high point, and mean firmness for brand D were 14.3 to 17.2 g/cm wire, 19.9 to 23.3 g/cm wire, and 17.8 to 19.9 g/cm wire. There was an approximate 1Q-g spread for each measurement of brand C compared with only a 3-g spread for brand D. High variability in low and high point measurement within a sample indicate a lack of uniformity in curd firmness. CONCLUSION
Computerization of the curd finnness meter, through an interface to an Apple lIe, improved the efficiency and accuracy of curd firmness measurement and data analysis. The lowest, highest, and mean fmnness points are obtained from analysis of the computer-generated, force time curve. Mean fmnness values are useful to distinguish among samples, and the low and high firmness points give added infonnation on variability within samples. ACKNOWLEDGMENTS
The authors wish to thank Joanne Elsaesser for conducting the curd firmness analysis of the test samples. Journal of Dairy Science Vol. 73,
No.6. 199<1
1652
MACKIE ET AL.
REFERENCES 1 Emmons, D. B., D. C. Beckett, and E. Lannond. 1972. Physical properties and storage stability of milk-based puddings made with varions starches and stabilizers. Can. lost Food Sci. Technol. J. 5(2):72. 2 Emmons, D. B., and W. V. Price. 1959. A curd fumness
Journal of Dairy Science Vol. 73,
No.6, 1990
test for cottage cheese. J. Dairy Sci. 42:553. 3 Irvine, D. M. 1955. The development of dairyworld cheese and factors influencing its characteristics. Ph.D. Diss., Univ, Wisconsin, Madison. 4 Voisey, P. W., andD. B. Emmons. 1966. Modification of the curd firmness test for cottage cheese. J. Dairy Sci. 49: 93.
ABSTRACT
The curd fIrmness meter was inter faced with an Apple IIe computer to in crease both the efficiency of the instru ment and the accuracy of the instrumental measurements. The computerization al lows for collection of real-time data, graphical analysis, and maintenance of results in a data base capable of generat ing reports. The newly modified curd firmness meter can measure the firmness of cheeses and gels. The mean, lowest, and highest firmness points are obtained from the computer-generated. force-time curve. The mean firmness values distin guish among samples, and the low and high firmness points give information on variability within samples. (Key words: curd firmness, computerized meter, cheese) INTRODUCTION
Several modifications of the Cherry-Burrell curd-tension meter have taken place over the last 30 yr. Each change has improved both the accuracy and efficiency of the instrument. In 1955, Irvine (3) modified the meter to measure the resistance to passage of a wire through a block of Cheddar cheese. Emmons and Price (2) made a further adaptation to allow the measurement of cottage cheese curd firmness. The instrumentally measured resistance was found to be directly related to the fIrmness of the curd as determined by a sensory panel for both Cheddar and cottage cheese. The curd firmness meter can also be used to measure gel firmness in products such as yogurts, puddings, and sour cream.
Received September 25, 1989. Accepted January 11, 1990. Ipood Research Centre Contribution Number 828. 2pood Research Centre Building 55. 3Systems and Consulting Division, Carling Building. 1990 J Dairy Sci 73:1648-1652
~ 1966, modifications were implemented by ':'Olsey and Emmons (4) to increase the preci s10n of measurement and to provide a perma nent record of each measurement on a strip chart. The three major changes were: 1) the dietetic scale was replaced with a strain-gauge transducer coupled to an amplifier and strip chart recorder, 2) the length of the cutting edge was increased from one wire to three parallel wires, and 3) the drive mechanism was changed from a gear-drive to a screw-drive. This paper describes a fuither modification, which increases the efficiency of the instrument (less time to obtain results) and the accuracy of results by interfacing the curd firmness meter with an Apple He computer. The reader is referred to the Voisey and Emmons (4) and Emmons et al. (1) papers for a complete de scription and detailed illustrations of the ten sion or curd firmness meter. A brief description of the apparatus will be repeated in this paper to help the reader understand the basic princi ples in instrumental curd firmness measure ment.
INSTRUMENTATION
When measuring the firmness of a cheese, the sample is placed into a slotted aluminum cylindrical container (Figure 1). Three parallel wires held in a circular frame pass through the slotted container at a rate of .29 crn/s. When measuring the firmness of a gel, the sample is p~sented to the meter in any appropriate con tamer, such as a beaker, cup, or bowl (Figure 2). Two concentric circular knives cut through the gel at a rate of .29 crn/s. The force applied by either the cutting wires or knives is trans ferred to a strain-gauge transducer and produces an output voltage which is proportional to the force applied. This output voltage is amplified and the signal is recorded. The newly modified curd firmness meter is interfaced to a computer (Figure 3), which re places the strip-chart recorder previously used. The computerization enables users to collect
1648
OUR INDUSTRY TODAY
Figure I. Slotted aluminum container and 3 cutting wires for cheese firmness measurement.
data on a real-time basis from the strain-gauge, perfonn automatic graphical analysis of the data, and maintain the results in a data base capable of generating reports. The system is based on an Apple lIe with 64 K random access memory (RAM) running DOS 3.3 from a 128-K system software disk drive and a 128-K data disk drive or a hard disk. The analysis program runs in compiled BASIC (Ap plesoft BASIC) together with a utility which automatically relocates DOS to the upper 13K of RAM. Other components include an Interac tive Structures AID conversion card, a Moun tain Hardware clock, and a printer capable of graphics and compatible with Mannesman Tally or Epson graphics. DATA COLLECTION AND ANALYSIS
To use the curd finnness meter, the instru ment (strain-gauge) is ftrst calibrated with a
1649
Figure 2. Circular knives for gel firmness measurement.
known laboratory weight. An idea of the ap proximate firmness of the sample to be tested is beneficial in choosing the appropriate calibra tion weight. The ideal calibration weight should be 25 to 33% of the expected maximum force. After the calibration is complete, the calibration curve results are automatically printed, and the user returns to the main data collection menu. To begin data collection, a file name is entered for the test sample. The sample-filled container is then placed on the strain-gauge, the weight of the cheese and container are tared, and the wires or knives start their downward stroke. For a solid cheese, such as Cheddar, a block is cut to just fit inside the cylinder (5.5 cm in diameter, 8.5 cm in height). For cottage cheese, approximately ZOO g of sample are spooned into the cylinder. The cottage cheese is packed finnly after each spoonful to minimize pockets of air or liquid between the curd parti cles. A 2-kg cylindrical weight is placed on the Journal of Dairy Science Vol. 73,
No.6, 1990
1650
MACKIE ET AL.
Figure 3. 1be curd firmness meter interfaced with an Apple ITe computer.
curd for approximately lOs to pack the curd unifonnly. A plastic sleeve is placed around the container during this pressing stage to prevent the escape of curds through the slots in the container. The amount of gel sample depends on the diameter and height of the container used. All samples are kept at 5°e until the firmness measmement is taken. During the curd firmness measmement, the force required for the wires or knives to cut through the sample is recorded as a function of time (Figures 4 and 5). The force builds up from zero (point A) as the sample compresses under the load The wires or knives eventually cut into the sample, after which the force re corded will fluctuate as the wires pass through the sample to point B, the bottom of the stroke. The user can continue data collection on subsequent samples or proceed to the data anal ysis function. There is a choice of two types of curve analysis: Cheddar (solid) cheese or cot tage cheese. With the Cheddar cheese curve analysis, a vertical line is drawn from the 2.5-s time point upward to intersect (0) with the test sample curve (Figure 4). The values are calculated from the curve after this intersection point. The 2.5-s time point ensures the cutting head has penetrated the sample sufficiently. The Cheddar cheese analysis is also used for gel firmness analysis. With the cottage cheese Journal of Dairy Science Vol. 73,
No.6, 1990
...
F
~
E
...~
C
TIME (sl
Figure 4. Typical computer-generated, force-time curve for solid cheese or gels. A is the point at which the wires make contact with the cheese sample, B is the point of completion of the downward stroke of the wires through the cheese sample, C is the lowest fumness point, D is the curve intersection point where the curve analysis begins, E is the mean firmness, and F is the highest flmllless point
curve analysis (Figme 5), a horizontal line is drawn from the lowest fluctuation (C) to inter sect with the initial vertical rise in force (0). A vertical line is then drawn through the point of intersection and all values are calculated from that point. Although this intersection point (0) may actually be before complete insertion of the cutting head into the sample has taken place, this analysis allows for all the variation in finnness of the individual cottage cheese curds to be incorporated into the calculation of the mean firmness. The same information is obtained from both analyses: mean force (E), low point (C), and high point (F). The analyzed results are printed along with the curve and include filename as signed to the test sample, mean force (g), low point (g), high point (g), calibration factor, test date, analysis type (cottage or Cheddar), along with other program parameters. The computer generated results eliminate any inaccuracies previously possible when visually extracting the firmness points from the strip chart recorder graph.
1651
OUR INDUSTRY TODAY
TABLE 1. Means,l standard deviations, and coefficients of variation (%) for low point, mean, and high point curd firmness measurement.
B w
E
1i! c o u.
Brand
Firmness (g/cm wire)
A
B
C
D
Low point SD CV
21.7 2.84 13.1
21.1 1.29 6.1
16.5 2.84 17.2
Mean SD CV
26.6 1.92 7.2
24.2 .71 3.0
19.5 2.76 14.2
15.6 .82 5.2 18.6 .63 3.4
High point SD CV
33.0 2.18 6.6
27.7 1.31 4.7
23.1 2.89 12.5
21.6 1.05 4.9
IMeans of 10 measuremenrs.
TIME (s)
Figure 5. Typical computer generated, foree-time curve for cottage cheese. A is the point at which the wires make contact with the cheese sample, B is the point of comple tion of the downward stroke of the wires through the cheese sample, C is the lowest firmness point, D is the curve intersection point where the curve analysis begins, E' is the mean fumness, and F is the highest firmness point.
EXPERIMENTAL EXAMPLE
To highlight the usefulness of the infonna tion that can be obtained from this computer ized curd finnness meter, demonstrative results from a study conducted at the Food Research Centre, Agriculture Canada, Ottawa, on cottage cheese are presented and discussed. Five con tainers of each of four commercially available brands of 2% milk fat (500 ml) creamed cot tage cheese were purchased. All five containers for each brand were from the same production lot, and the closest "best before dates" were purchased among brands. Samples were kept at SoC until evaluation. Two instrumental curd finnness measurements were taken from each container for a total of 10 finnness measure ments per brand. There was a difference among the cheeses (Table 1) for mean, low point, and high point finnness. Brand A was the most firm, and brands C and D were the least firm. Attention should be drawn to the standard deviations and coefficients of variation. There was more varia-
tion in firmness of brand C than the other brands, except for the low point measurement for brand A From the computer printout, the individual measured points can be examined for each test sample. For example, brand C had a range in low point measurement from 12.5 to 22.8 g/cm wire, in the high point measurement from 19.0 to 29.1 g/cm wire, and in mean firmness estimation from IS.9 to 25.8 g/cm wire. In comparison, the ranges in low point, high point, and mean firmness for brand D were 14.3 to 17.2 g/cm wire, 19.9 to 23.3 g/cm wire, and 17.8 to 19.9 g/cm wire. There was an approximate 1Q-g spread for each measurement of brand C compared with only a 3-g spread for brand D. High variability in low and high point measurement within a sample indicate a lack of uniformity in curd firmness. CONCLUSION
Computerization of the curd finnness meter, through an interface to an Apple lIe, improved the efficiency and accuracy of curd firmness measurement and data analysis. The lowest, highest, and mean fmnness points are obtained from analysis of the computer-generated, force time curve. Mean fmnness values are useful to distinguish among samples, and the low and high firmness points give added infonnation on variability within samples. ACKNOWLEDGMENTS
The authors wish to thank Joanne Elsaesser for conducting the curd firmness analysis of the test samples. Journal of Dairy Science Vol. 73,
No.6. 199<1
1652
MACKIE ET AL.
REFERENCES 1 Emmons, D. B., D. C. Beckett, and E. Lannond. 1972. Physical properties and storage stability of milk-based puddings made with varions starches and stabilizers. Can. lost Food Sci. Technol. J. 5(2):72. 2 Emmons, D. B., and W. V. Price. 1959. A curd fumness
Journal of Dairy Science Vol. 73,
No.6, 1990
test for cottage cheese. J. Dairy Sci. 42:553. 3 Irvine, D. M. 1955. The development of dairyworld cheese and factors influencing its characteristics. Ph.D. Diss., Univ, Wisconsin, Madison. 4 Voisey, P. W., andD. B. Emmons. 1966. Modification of the curd firmness test for cottage cheese. J. Dairy Sci. 49: 93.