CHEESE TECHNOLOGY

Module 10. Yield of cheese

Lesson 24
FACTORS AFFECTING CHEESE YIELD

24.1 Factors Affecting Cheese Yield

Factors affecting cheese yield can broadly be listed into two groups:

24.1.1 Cheese yield potential of milk

i) Breed of cow

ii) Variation between individual cows

iii) Stage of lactation

iv) Seasonal changes in climate and natural feed

v) The type of feed and level of feeding

vi) Problems due to diseases, especially mastitis

vii) Milking procedures, such as the time that elapses between milkings and whether milked by hand or by machines

viii) Effect of genetic variants on milk composition

24.1.2 Processing conditions that affect cheese yield

i) Storage of milk

ii) Milk standardization

iii) Concentration of milk

iv) Growth media used for bulk starter preparation

v) Type of starter culture used

vi) Heat treatment of milk

vii) Homogenization of milk

viii) Addition of CaCl₂ to milk

ix) Type of coagulant used

x) Curd firmness

xi) Type of vat

xii) Curd handling system

xiii) Cooking of curd

xiv) Cheddaring of curd

xv) Washing of curd

xvi) Proportion of salt added

xvii) Pressure applied

xviii) Loss of moisture during storage

The major factors that affect yield of cheese are discussed here. They can be broadly classified in two categories: 1) Uncontrollable factors and 2) Controllable factors. The major factor which is beyond the control of a cheese maker is the composition of milk. The other uncontrollable factor is the equipment used by the cheese maker. Various controllable factors are those related to the method of manufacturing and the processing conditions used while cheesemaking. The principal factors that influence cheese yield are discussed below:

24.1.3 Milk composition

One of the most important factors that affect cheese yield is the milk composition particularly casein and fat content. As already mentioned, cheese yield can be predicted by using the general equation Y= aF + bC. This shows that cheese yield is linearly related with fat and casein content of milk. The greater contribution of casein is expected, as it forms the continuous paracasein sponge-like network that occludes the fat and serum phases. In contrast, fat on its own has little water-holding capacity. Occluded moisture contributes directly to cheese yield and indirectly owing to the presence of dissolved solids, including whey proteins, κ-casein glycomacro peptide, lactate, and soluble milk salts. Fat generally contributes more than its own weight to Cheddar-type cheese (yield increases by about 1.16 kg/kg milk fat). This greater than pro-rata increase, is due to the increase in the level of moisture in nonfat substance as the fat content of the cheese increases. Fat is occluded in the pores of the paracase in network of the cheese and impedes syneresis. The occluded fat globules physically limit aggregation of the surrounding paracasein network and therefore reduce the degree of matrix contraction and moisture expulsion. Hence, as the fat content of the curd is increased, it becomes more difficult to expel moisture, and the moisture-protein ratio increases. However, if the moisture in nonfat substance is maintained constant (e.g. by process modifications such as reduction of curd particle size and slight elevation of the scald temperature), fat contributes less than its own weight to cheese yield (~ 0.9 kg/kg), owing to the fact that about 8-10% of the milk fat is normally lost in the whey.

The coefficients a and b depend on the composition of milk, the manufacturing procedure, equipment design and retention of fat and casein in the cheese. All those factors that affect milk composition, indirectly affect the yield also. Some such factors are species and breed of the animal, stage of lactation, seasonal variations, etc.

24.1.4 Holding milk at low temperature

When it is not possible for the cheesemakers to start cheesemaking soon after milk reception, the milk is stored in cold storages for some hours, depending on the manufacturing schedule. This action of storing milk at refrigerated temperature results in some physico-chemical changes in milk, which include:

• Solubilization of casein and colloidal calcium phosphate which leads to increase in serum caseins, thereby increasing loss in whey.

• Growth of psychrotrophic bacteria which leads to release of enzymes like proteases and lipases.

• Increase in free fat levels owing to lipase action.

The increased serum casein level can be reversed by pasteurization and thus, the effect of cold storage is nullified but the production of proteases cause protein breakdown into peptides. Some of these peptides are soluble in the serum phase and do not coagulate during curd formation. They are lost in whey leading to a decrease in cheese yield. The reduced casein level has an effect of curd shattering and weak coagulum, thereby increasing fat loss in whey. The dual effect of losing casein and fat in whey reduces the cheese yield considerably.

24.1.5 Heat treatment of milk

Cheese milk can be given heat treatments like thermization, pasteurization, etc. Heat treatment denatures whey proteins and results in their inclusion in the gel and thereby increase yield of cheese. The degree of whey protein denaturation determines the extent of their recovery in cheese. Thermization is done when milk is to be stored for long before making cheese. As discussed in the previous section, cold storage of milk leads to production of enzymes like proteases and lipases. Thermization prevents growth of psychrotrophs in milk, prevents casein solubilization and thus increases cheese yield. Pasteurization of milk (72°C, 15 s) denatures whey proteins to a lower level and thus the cheese yield is only slightly increased. The severe the heat treatment, more is the resultant increase in cheese yield.

24.1.6 Addition of CaCl₂

Addition of CaCl₂ at the rate of 0.02% in cheese milk is a common practice. This results in strengthening the curd, making it less susceptible to shattering at the time of cutting and stirring. This reduces the chances of fat and protein loss in whey and thus increases cheese yield.

24.1.7 Type of rennet

Type of rennet used for coagulation affects cheese yield as it affects the extent of proteolysis. The rennet having more proteolytic activity solubilizes casein and increases its loss in whey. Proteolytic rennet reduces cheese yield significantly only when the pH of the whey at the time of drainage is below 6.0 as in the case of Blue cheese and Camembert cheese.