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Cheese | Curd Syneresis
Curd Syneresis J A Lucey, University of Wisconsin–Madison, Madison, WI, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction Syneresis is the loss of serum (whey) from the curd. Syneresis is a process whereby whey is separated from curd particles, and as a result of the expulsion of whey the curd particles shrink in volume. It is probably more correct to describe gel shrinkage as a process that forces or ‘squeezes’ whey out of the matrix through the pores. The aqueous phase in rennet gels is mostly physically trapped and not chemically bound. Rennet-induced milk gels remain apparently stable (i.e., no visible collapse) for several hours if the gels are left undisturbed but they synerese rapidly if disturbed by cutting or by wetting the gel surface. The tendency to exhibit syneresis in gels can be viewed as the reverse of the swelling behavior. Cheesemaking can be viewed as a dehydration process and syneresis is the crucial method by which most of the moisture is lost from curd particles. Since syneresis is the main method available to cheesemakers for controlling cheese moisture content, it is also the process that is mostly manipulated during cheesemaking and various dehydration approaches help to facilitate differentiation between cheese varieties (Table 1).
the liquid, p the pressure acting on the liquid, and x the distance over which the liquid must flow. The permeability of renneted gels increases with time after renneting (even when the gel is not cut or broken) due to microsyneresis or the formation of larger pores in the matrix. Initially, the rate of syneresis is very high but due to shrinkage, the gel becomes locally denser, the rheological modulus increases, and permeability decreases. Thus, after the gel has undergone considerable contraction (when shrinkage is initiated by surface wetting), further shrinkage is inhibited by the reduced permeability and the increased resistance of the matrix to further deformation. In the model of Darcy, it is assumed that the matrix allows the outflow of whey without collapsing or resisting. However, in the case of rennet gels, rapid shrinkage of curd particles occurs. In practice, syneresis of curd particles occurs in three dimensions simultaneously and is much harder to study than the one-dimensional model. Curd grains rapidly collapse once removed from (being suspended in) whey, making measurements difficult.
Mechanism of Syneresis Measurement or Modeling of the Syneresis of Rennet Gels Various (mostly empirical) techniques have been used to measure syneresis of curd (Table 2). Because of the complexity of modeling of shrinkage of curd particles in various dimensions, one-dimensional syneresis of thin gel slabs (where the diameter is much larger than the thickness) has been used to model the syneresis process. In these one-dimensional syneresis experiments, the gel is not cut but rather the surface is wetted, which is sufficient pressure to initiate syneresis. One-dimensional syneresis of rennet-induced milk gels is related to the flow of liquid (whey) through the network (since liquid flows out of the gel concomitantly with gel shrinkage) and is governed by the equation of Darcy: v¼
Bp x
where v is the superficial flow velocity of the syneresing liquid, B the permeability coefficient, the viscosity of
The initial rennet-induced gel should be viewed as a weakly stabilized, transient (dynamic) network. Hydrolysis of the -casein hairs on casein micelles results in the loss of both steric and charge stabilization mechanisms. The renneted micelles then aggregate and form a network. The interactions between rennet-altered micelles are weak (ionic bridges, hydrophobic interactions) and the resultant matrix has high bond mobility (or bond relaxation, as indicated by the high values for the loss tangent parameter from rheological measurements). If bonds between aggregating particles are reversible (at least for a short period after gelation), rearrangements may occur in the aggregates/clusters formed as well as in the gel network. In the initial rennet gel network, bonds are breaking and reforming, which increases the possibility of rearrangements. Experienced cheesemakers know that if they wish to promote syneresis (or decrease the cheese moisture content) they should cut the rennet gel when it is still very weak. After gelation, there is ongoing particle fusion and the formation of additional cross-links between the caseins. With increasing time after renneting, rennet gels
591
592 Cheese | Curd Syneresis Table 1 Approaches used to increase or decrease the syneresis (moisture content) of cheese curds Decrease moisture content
Increase moisture content
Avoid excessive whey protein denaturation
Use high heat treatment of milk (or the use of ingredients with denatured whey proteins, such as starter media) Use homogenization of the cheesemilk Use liquid precheese Use preacidification of milk Cut curd into larger pieces Cut the gel when it is firmer, that is, wait longer after visible gelation Use lower cooking temperatures Use shorter cooking (stirring) times Use cold water for washing or rinsing curd Avoid dry-stirring of the curd or use shorter stirring times
Avoid homogenization of cheesemilk Use milk with normal protein levels (e.g., 3.5%) Avoid preacidification of milk Cut curd into smaller pieces Cut the gel softer, that is, sooner after visible gelation Use higher cooking temperatures Use longer cooking (stirring) times Use hot water for washing or rinsing curd Use more dry-stirring of curd after whey drainage (stirred curd) Apply pressure in forms/molds/hoops Apply mechanical dewatering of curd (e.g., separators or membrane filtration) Use higher salting level
Do not press curds in molds Avoid the use of mechanical dewatering devices Use lower salt level
Table 2 Techniques used to quantify syneresis One-dimensional shrinkage of curd slabs Amount of whey expelled as a result of syneresis Monitoring of tracer dyes Dry matter content of curd sampled during shrinkage Density of curd grains Light scattering properties of the curd/whey mixture Low-resolution nuclear magnetic resonance (NMR)
increase in stiffness and in resistance to deformation, which act to reduce the ability of the network to rearrange its microstructure. Thus, waiting for the gel to become firmer before cutting makes it harder for that gel to undergo extensive syneresis and therefore the cheese has higher moisture content. There is some tendency or driving force promoting increased casein interactions. Recently, views of syneresis suggest that this tendency could be viewed as a type of phase separation in a viscoelastic transient gel system. It is possible that the renneted micelles have surfaces that are only partly attractive (due to the high pH) and this promotes shuffling of particles to reduce repulsion (increase attraction). It could also be that the completion of the hydrolysis of all the -casein hairs by rennet, after the formation of a weak network, alters the attractive/ repulsive balance in the system. The incorporation of additional particles in the network (i.e., micelles where hydrolysis of -casein was completed only after network formation) results in the formation of new physical crosslinks between protein strands, which may promote tensile stresses in the system resulting in strand breakage. Micelles that are only partly attached to the network (dangling ends) at the point of gelation could become ‘fully’ attached to the matrix with aging. An important aspect of the syneresis mechanism in cheese curd is the ability of the initial gel (coagulum) to
retain its shape after cutting. Cheesemakers wait until they can subjectively determine that the gel can withstand the cutting process. Often they evaluate this by cutting the gel with a spatula/knife and they observe if the cut gel surface does not rapidly collapse. The retention of structure in the curd pieces is critical in the creation of a large amount of exposed surfaces through which whey/serum can easily be expelled. The weight of the curd particles and gravity and collisions between curd particles (e.g., as a result of stirring) encourage the compression/deformation of curd particles, which promotes squeezing out of whey. In order for rennet gels to undergo syneresis, the network must be flexible enough to be able to rearrange itself into a smaller and more compact matrix. Syneresis of gels can occur either spontaneously or more commonly as a result of some physical stresses applied during cheesemaking. Syneresis can also occur in gels due to environmental changes, for example, decrease in pH or increase in temperature. It has been suggested that there is in rennet gels an ‘endogenous syneresis pressure’, that is, a pressure within the gel that is causing spontaneous syneresis or the syneresis of wetted gels. It has not been possible to measure experimentally this endogenous pressure since the predicted values are very low. The rate of syneresis increases initially as a function of time after renneting but decreases at longer times, presumably due to fusion of para-casein micelles and a reduction in the permeability of the contracting network. The mechanism responsible for the strong tendency of rennet-induced milk gels to synerese is related to (extensive) rearrangements of the casein network, which occur after gel formation. The rearrangement process is accelerated and is more extensive at high temperatures. Aging of rennet-induced gels results in a coarsening (sometimes called ‘microsyneresis’) of the gel (i.e., rearrangements) and an increase in the fractal dimensionality.
Cheese | Curd Syneresis
In rennet-induced milk gels, low gel stiffness (elastic modulus) and high values of the loss tangent (tan at low frequencies) are important rheological conditions that facilitate rearrangements of bonds (when these rheological measurements are made at approximately the same timescale over which rearrangement processes related to syneresis in these gels are estimated to occur). Rearrangements of casein particles into a more compact structure would increase the number of bonds and hence decrease the total free energy of the system. However, the particles are part of the gel network, which must be deformed or broken locally to form new junctions. In cheesemaking, conditions such as cutting, stirring, acid production, and the increase in temperature that occurs during cooking all encourage syneresis and the rearrangement processes that facilitate syneresis of the gel network.
Factors That Impact Syneresis Syneresis is very much dependent on the pH of curd. Small adjustments of pH (i.e., decreasing pH from 6.5 to 6.3), such as in the preacidification of cheesemilk, can result in an overall reduction in syneresis. This is due to the increase in the stiffness of rennet gels that occurs with the small reduction in pH, which is due also to the reduced electrostatic repulsion (and thereby increased attractive interactions) between particles. A larger decrease in pH (e.g., from pH 6.3 to 5.2) promotes greater syneresis of rennet gels. This is presumably due to solubilization of intraparticle insoluble calcium phosphate cross-links, which increases the flexibility of casein particles. Acid-induced milk gels (pH 4.6) undergo
593
much less syneresis than rennet-induced gels (Figure 1). Due to the different interactions present in acid-induced gels, the bonds are less mobile (lower loss tangent) and strands are less susceptible to rearrangements. High heat treatment of milk results in reduced syneresis. High heat treatment (greater than pasteurization) causes denaturation of whey proteins, and at the normal pH of milk, most of these whey proteins become associated with micelle surface. The presence of denatured whey proteins on the micellar surface impedes fusion of renneted micelles and limits the rearrangement of strands and clusters, which is a requirement of the syneresis process. Syneresis is enhanced by higher coagulation or cooking temperatures. Temperature increases the thermal motion of particles and strands in the network. The stiffness of the rennet gel also decreases with increasing cooking temperature. There is a decrease in the voluminosity (particles shrink in size) with increasing temperature, which reduces the potential contact area between clusters/strands. Rennet gels made from highly concentrated milk, where the milk is concentrated to the required total solids content of that cheese variety (i.e., liquid precheese), hardly undergo syneresis. Presumably the resistance to deformation or breakage of strands in the matrix is too high to facilitate syneresis. In highly concentrated milk, the number of protein–protein bonds in the strands and junctions of the gel matrix becomes very high. This lack of syneresis is exploited in the so-called cast cheese (e.g., UF cast Feta), where an ultrafiltration retentate is heated and along with rennet and cultures/enzymes is filled directly into containers where it sets to a gel (cheese). Proteolysis of caseins, for example, by enhanced plasmin activity in mastitic or late-lactation milk, results in
Height of gel as a % of original height
100
80 Rennet gel Acid gel
60
40
20
0 0
5
10
15
20
25
Time after initiating syneresis by wetting the surface (h) Figure 1 Syneresis of one-dimensional slabs of rennet-induced (solid line) and acid-induced (dotted line) gels as a function of time. Rennet gels were tested 1 h after rennet addition and the acid gels were tested at pH 4.6 for gelation induced by glucono--lactone. Reproduced from Lucey JA (2001) The relationship between rheological parameters and whey separation in milk gels. Food Hydrocolloids 15: 603–608 with permission from Elsevier.
594 Cheese | Curd Syneresis
weak gels. Cheeses made from milk that has degraded caseins also have higher moisture contents. Presumably, this reflects a better contraction ability of intact rennet gels compared to gels made from hydrolyzed caseins. See also: Cheese: Acid- and Acid/Heat-Coagulated Cheese; Cheese Rheology; Gel Firmness and Its Measurement; Overview; Rennets and Coagulants; Rennet-Induced Coagulation of Milk; Salting of Cheese. Heat Treatment of Milk: Heat Stability of Milk. Milk Proteins: Casein, Micellar Structure.
Further Reading Dejmek P and Walstra P (2004) The syneresis of rennet-coagulated curd. In: Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) Cheese: Chemistry, Physics and Microbiology, Vol. 1: General Aspects, 3rd edn., pp. 71–103. London: Elsevier Academic Press. Fox PF, Guinee TP, Cogan TM, and McSweeney PLH (2000) Postcoagulation treatment of renneted milk gel. In: Fundamentals of Cheese Science, pp. 138–152. Gaithersburg, MD: Aspen.
Green ML and Grandison AS (1993) Secondary (non-enzymatic) phase of rennet coagulation and post-coagulation phenomena. In: Fox PF (ed.) Cheese: Chemistry, Physics and Microbiology, Vol. 1: General Aspects, 2nd edn., pp. 101–140. London: Chapman & Hall. Horne DS and Banks JM (2004) Rennet-induced coagulation of milk. In: Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) Cheese: Chemistry, Physics and Microbiology, Vol. 1: General Aspects, 3rd edn., pp. 47–70. London: Elsevier Academic Press. Lomholt SB and Qvist KB (1999) The formation of cheese curd. In: Law BA (ed.) Technology of Cheesemaking, pp. 66–98. Sheffield, UK: Sheffield University Press. Lucey JA (2001) The relationship between rheological parameters and whey separation in milk gels. Food Hydrocolloids 15: 603–608. Lucey JA (2002) Formation and physical properties of milk protein gels. Journal of Dairy Science 85: 281–294. Pearse MJ and MacKinlay AG (1989) Biochemical aspects of syneresis: A review. Journal of Dairy Science 72: 1401–1407. van Vliet T and Walstra P (1994) Water in casein gels: How to get it out or keep it in. Journal of Food Engineering 22: 75–88. Walstra P, van Dijk HJM, and Geurts TJ (1985) The syneresis of curd. 1. General considerations and literature review. Netherlands Milk and Dairy Journal 39: 209–246. Walstra P and van Vliet T (1986) The physical chemistry of curd making. Netherlands Milk and Dairy Journal 40: 241–259.
Introduction Syneresis is the loss of serum (whey) from the curd. Syneresis is a process whereby whey is separated from curd particles, and as a result of the expulsion of whey the curd particles shrink in volume. It is probably more correct to describe gel shrinkage as a process that forces or ‘squeezes’ whey out of the matrix through the pores. The aqueous phase in rennet gels is mostly physically trapped and not chemically bound. Rennet-induced milk gels remain apparently stable (i.e., no visible collapse) for several hours if the gels are left undisturbed but they synerese rapidly if disturbed by cutting or by wetting the gel surface. The tendency to exhibit syneresis in gels can be viewed as the reverse of the swelling behavior. Cheesemaking can be viewed as a dehydration process and syneresis is the crucial method by which most of the moisture is lost from curd particles. Since syneresis is the main method available to cheesemakers for controlling cheese moisture content, it is also the process that is mostly manipulated during cheesemaking and various dehydration approaches help to facilitate differentiation between cheese varieties (Table 1).
the liquid, p the pressure acting on the liquid, and x the distance over which the liquid must flow. The permeability of renneted gels increases with time after renneting (even when the gel is not cut or broken) due to microsyneresis or the formation of larger pores in the matrix. Initially, the rate of syneresis is very high but due to shrinkage, the gel becomes locally denser, the rheological modulus increases, and permeability decreases. Thus, after the gel has undergone considerable contraction (when shrinkage is initiated by surface wetting), further shrinkage is inhibited by the reduced permeability and the increased resistance of the matrix to further deformation. In the model of Darcy, it is assumed that the matrix allows the outflow of whey without collapsing or resisting. However, in the case of rennet gels, rapid shrinkage of curd particles occurs. In practice, syneresis of curd particles occurs in three dimensions simultaneously and is much harder to study than the one-dimensional model. Curd grains rapidly collapse once removed from (being suspended in) whey, making measurements difficult.
Mechanism of Syneresis Measurement or Modeling of the Syneresis of Rennet Gels Various (mostly empirical) techniques have been used to measure syneresis of curd (Table 2). Because of the complexity of modeling of shrinkage of curd particles in various dimensions, one-dimensional syneresis of thin gel slabs (where the diameter is much larger than the thickness) has been used to model the syneresis process. In these one-dimensional syneresis experiments, the gel is not cut but rather the surface is wetted, which is sufficient pressure to initiate syneresis. One-dimensional syneresis of rennet-induced milk gels is related to the flow of liquid (whey) through the network (since liquid flows out of the gel concomitantly with gel shrinkage) and is governed by the equation of Darcy: v¼
Bp x
where v is the superficial flow velocity of the syneresing liquid, B the permeability coefficient, the viscosity of
The initial rennet-induced gel should be viewed as a weakly stabilized, transient (dynamic) network. Hydrolysis of the -casein hairs on casein micelles results in the loss of both steric and charge stabilization mechanisms. The renneted micelles then aggregate and form a network. The interactions between rennet-altered micelles are weak (ionic bridges, hydrophobic interactions) and the resultant matrix has high bond mobility (or bond relaxation, as indicated by the high values for the loss tangent parameter from rheological measurements). If bonds between aggregating particles are reversible (at least for a short period after gelation), rearrangements may occur in the aggregates/clusters formed as well as in the gel network. In the initial rennet gel network, bonds are breaking and reforming, which increases the possibility of rearrangements. Experienced cheesemakers know that if they wish to promote syneresis (or decrease the cheese moisture content) they should cut the rennet gel when it is still very weak. After gelation, there is ongoing particle fusion and the formation of additional cross-links between the caseins. With increasing time after renneting, rennet gels
591
592 Cheese | Curd Syneresis Table 1 Approaches used to increase or decrease the syneresis (moisture content) of cheese curds Decrease moisture content
Increase moisture content
Avoid excessive whey protein denaturation
Use high heat treatment of milk (or the use of ingredients with denatured whey proteins, such as starter media) Use homogenization of the cheesemilk Use liquid precheese Use preacidification of milk Cut curd into larger pieces Cut the gel when it is firmer, that is, wait longer after visible gelation Use lower cooking temperatures Use shorter cooking (stirring) times Use cold water for washing or rinsing curd Avoid dry-stirring of the curd or use shorter stirring times
Avoid homogenization of cheesemilk Use milk with normal protein levels (e.g., 3.5%) Avoid preacidification of milk Cut curd into smaller pieces Cut the gel softer, that is, sooner after visible gelation Use higher cooking temperatures Use longer cooking (stirring) times Use hot water for washing or rinsing curd Use more dry-stirring of curd after whey drainage (stirred curd) Apply pressure in forms/molds/hoops Apply mechanical dewatering of curd (e.g., separators or membrane filtration) Use higher salting level
Do not press curds in molds Avoid the use of mechanical dewatering devices Use lower salt level
Table 2 Techniques used to quantify syneresis One-dimensional shrinkage of curd slabs Amount of whey expelled as a result of syneresis Monitoring of tracer dyes Dry matter content of curd sampled during shrinkage Density of curd grains Light scattering properties of the curd/whey mixture Low-resolution nuclear magnetic resonance (NMR)
increase in stiffness and in resistance to deformation, which act to reduce the ability of the network to rearrange its microstructure. Thus, waiting for the gel to become firmer before cutting makes it harder for that gel to undergo extensive syneresis and therefore the cheese has higher moisture content. There is some tendency or driving force promoting increased casein interactions. Recently, views of syneresis suggest that this tendency could be viewed as a type of phase separation in a viscoelastic transient gel system. It is possible that the renneted micelles have surfaces that are only partly attractive (due to the high pH) and this promotes shuffling of particles to reduce repulsion (increase attraction). It could also be that the completion of the hydrolysis of all the -casein hairs by rennet, after the formation of a weak network, alters the attractive/ repulsive balance in the system. The incorporation of additional particles in the network (i.e., micelles where hydrolysis of -casein was completed only after network formation) results in the formation of new physical crosslinks between protein strands, which may promote tensile stresses in the system resulting in strand breakage. Micelles that are only partly attached to the network (dangling ends) at the point of gelation could become ‘fully’ attached to the matrix with aging. An important aspect of the syneresis mechanism in cheese curd is the ability of the initial gel (coagulum) to
retain its shape after cutting. Cheesemakers wait until they can subjectively determine that the gel can withstand the cutting process. Often they evaluate this by cutting the gel with a spatula/knife and they observe if the cut gel surface does not rapidly collapse. The retention of structure in the curd pieces is critical in the creation of a large amount of exposed surfaces through which whey/serum can easily be expelled. The weight of the curd particles and gravity and collisions between curd particles (e.g., as a result of stirring) encourage the compression/deformation of curd particles, which promotes squeezing out of whey. In order for rennet gels to undergo syneresis, the network must be flexible enough to be able to rearrange itself into a smaller and more compact matrix. Syneresis of gels can occur either spontaneously or more commonly as a result of some physical stresses applied during cheesemaking. Syneresis can also occur in gels due to environmental changes, for example, decrease in pH or increase in temperature. It has been suggested that there is in rennet gels an ‘endogenous syneresis pressure’, that is, a pressure within the gel that is causing spontaneous syneresis or the syneresis of wetted gels. It has not been possible to measure experimentally this endogenous pressure since the predicted values are very low. The rate of syneresis increases initially as a function of time after renneting but decreases at longer times, presumably due to fusion of para-casein micelles and a reduction in the permeability of the contracting network. The mechanism responsible for the strong tendency of rennet-induced milk gels to synerese is related to (extensive) rearrangements of the casein network, which occur after gel formation. The rearrangement process is accelerated and is more extensive at high temperatures. Aging of rennet-induced gels results in a coarsening (sometimes called ‘microsyneresis’) of the gel (i.e., rearrangements) and an increase in the fractal dimensionality.
Cheese | Curd Syneresis
In rennet-induced milk gels, low gel stiffness (elastic modulus) and high values of the loss tangent (tan at low frequencies) are important rheological conditions that facilitate rearrangements of bonds (when these rheological measurements are made at approximately the same timescale over which rearrangement processes related to syneresis in these gels are estimated to occur). Rearrangements of casein particles into a more compact structure would increase the number of bonds and hence decrease the total free energy of the system. However, the particles are part of the gel network, which must be deformed or broken locally to form new junctions. In cheesemaking, conditions such as cutting, stirring, acid production, and the increase in temperature that occurs during cooking all encourage syneresis and the rearrangement processes that facilitate syneresis of the gel network.
Factors That Impact Syneresis Syneresis is very much dependent on the pH of curd. Small adjustments of pH (i.e., decreasing pH from 6.5 to 6.3), such as in the preacidification of cheesemilk, can result in an overall reduction in syneresis. This is due to the increase in the stiffness of rennet gels that occurs with the small reduction in pH, which is due also to the reduced electrostatic repulsion (and thereby increased attractive interactions) between particles. A larger decrease in pH (e.g., from pH 6.3 to 5.2) promotes greater syneresis of rennet gels. This is presumably due to solubilization of intraparticle insoluble calcium phosphate cross-links, which increases the flexibility of casein particles. Acid-induced milk gels (pH 4.6) undergo
593
much less syneresis than rennet-induced gels (Figure 1). Due to the different interactions present in acid-induced gels, the bonds are less mobile (lower loss tangent) and strands are less susceptible to rearrangements. High heat treatment of milk results in reduced syneresis. High heat treatment (greater than pasteurization) causes denaturation of whey proteins, and at the normal pH of milk, most of these whey proteins become associated with micelle surface. The presence of denatured whey proteins on the micellar surface impedes fusion of renneted micelles and limits the rearrangement of strands and clusters, which is a requirement of the syneresis process. Syneresis is enhanced by higher coagulation or cooking temperatures. Temperature increases the thermal motion of particles and strands in the network. The stiffness of the rennet gel also decreases with increasing cooking temperature. There is a decrease in the voluminosity (particles shrink in size) with increasing temperature, which reduces the potential contact area between clusters/strands. Rennet gels made from highly concentrated milk, where the milk is concentrated to the required total solids content of that cheese variety (i.e., liquid precheese), hardly undergo syneresis. Presumably the resistance to deformation or breakage of strands in the matrix is too high to facilitate syneresis. In highly concentrated milk, the number of protein–protein bonds in the strands and junctions of the gel matrix becomes very high. This lack of syneresis is exploited in the so-called cast cheese (e.g., UF cast Feta), where an ultrafiltration retentate is heated and along with rennet and cultures/enzymes is filled directly into containers where it sets to a gel (cheese). Proteolysis of caseins, for example, by enhanced plasmin activity in mastitic or late-lactation milk, results in
Height of gel as a % of original height
100
80 Rennet gel Acid gel
60
40
20
0 0
5
10
15
20
25
Time after initiating syneresis by wetting the surface (h) Figure 1 Syneresis of one-dimensional slabs of rennet-induced (solid line) and acid-induced (dotted line) gels as a function of time. Rennet gels were tested 1 h after rennet addition and the acid gels were tested at pH 4.6 for gelation induced by glucono--lactone. Reproduced from Lucey JA (2001) The relationship between rheological parameters and whey separation in milk gels. Food Hydrocolloids 15: 603–608 with permission from Elsevier.
594 Cheese | Curd Syneresis
weak gels. Cheeses made from milk that has degraded caseins also have higher moisture contents. Presumably, this reflects a better contraction ability of intact rennet gels compared to gels made from hydrolyzed caseins. See also: Cheese: Acid- and Acid/Heat-Coagulated Cheese; Cheese Rheology; Gel Firmness and Its Measurement; Overview; Rennets and Coagulants; Rennet-Induced Coagulation of Milk; Salting of Cheese. Heat Treatment of Milk: Heat Stability of Milk. Milk Proteins: Casein, Micellar Structure.
Further Reading Dejmek P and Walstra P (2004) The syneresis of rennet-coagulated curd. In: Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) Cheese: Chemistry, Physics and Microbiology, Vol. 1: General Aspects, 3rd edn., pp. 71–103. London: Elsevier Academic Press. Fox PF, Guinee TP, Cogan TM, and McSweeney PLH (2000) Postcoagulation treatment of renneted milk gel. In: Fundamentals of Cheese Science, pp. 138–152. Gaithersburg, MD: Aspen.
Green ML and Grandison AS (1993) Secondary (non-enzymatic) phase of rennet coagulation and post-coagulation phenomena. In: Fox PF (ed.) Cheese: Chemistry, Physics and Microbiology, Vol. 1: General Aspects, 2nd edn., pp. 101–140. London: Chapman & Hall. Horne DS and Banks JM (2004) Rennet-induced coagulation of milk. In: Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) Cheese: Chemistry, Physics and Microbiology, Vol. 1: General Aspects, 3rd edn., pp. 47–70. London: Elsevier Academic Press. Lomholt SB and Qvist KB (1999) The formation of cheese curd. In: Law BA (ed.) Technology of Cheesemaking, pp. 66–98. Sheffield, UK: Sheffield University Press. Lucey JA (2001) The relationship between rheological parameters and whey separation in milk gels. Food Hydrocolloids 15: 603–608. Lucey JA (2002) Formation and physical properties of milk protein gels. Journal of Dairy Science 85: 281–294. Pearse MJ and MacKinlay AG (1989) Biochemical aspects of syneresis: A review. Journal of Dairy Science 72: 1401–1407. van Vliet T and Walstra P (1994) Water in casein gels: How to get it out or keep it in. Journal of Food Engineering 22: 75–88. Walstra P, van Dijk HJM, and Geurts TJ (1985) The syneresis of curd. 1. General considerations and literature review. Netherlands Milk and Dairy Journal 39: 209–246. Walstra P and van Vliet T (1986) The physical chemistry of curd making. Netherlands Milk and Dairy Journal 40: 241–259.