20.0 Cheese and Cheese Making

20.2 Background.

• Cheese has been made in most cultures from ancient times.
• Cheese is a milk concentrate, the basic solids of which consists mainly of protein (caseins), and fat. The residual liquid is called whey.
• The casein and fat in milk is concentrated about 10 times in production of hard cheese and some semi-hard types of cheese.
• No strict definition of the concept of cheese is possible, as so many variants exist.

20.3 Terminology for Classification of Cheese. Codex Alimentarius, FAO/WHO, has issued Standard A6 as a definition for cheese products.

Cheese is the fresh or ripened solid or semi-solid product in which the whey protein/casein ratio does not exceed that of milk obtained:

• (a) by coagulating (whole or partly) the following raw materials: milk, skimmed milk, partly skimmed milk, cream, whey cream, or buttermilk, through the action of rennet or other suitable coagulating agents, and by partly draining the whey resulting from such coagulation; or
• (b) by processing techniques involving coagulation of milk and/or materials obtained from milk which give an end product which has similar physical, chemical and organoleptic characteristics as the product named under Classification of Cheese.

20.4 Classification of Cheese. The moisture content of cheese serves as the first term to distinguish various categories. The fat content is the second term, and curing characteristics represent a third term.

20.4.2 Fat Content. The fat content of cheese is reported on a dry solids basis (FDB), calculated as shown:

20.4.3 Curing Characteristics.

1. Cured or ripened cheese is cheese which is not ready for consumption shortly after manufacture but which must be held for such time, at such temperature, and under such conditions as will result in the necessary biochemical and physical changes characterizing the cheese.
1. Mould cured or mould ripened cheese is a cured cheese in which the curing has been accomplished primarily by the development of characteristic mould growth throughout the interior and/or on the surface of the cheese.
1. Uncured, unripened, or fresh cheese is cheese which is ready for consumption shortly after manufacture.

20.4.4 Designation of Terms for Classification of Cheese. The following three terms apply to all cheeses covered by the A6 Standard under Codex Alimentarius. However, this classification does not preclude the designation of more specific requirements in individual cheese standards.

20.5 General Procedure from Milk to Hard and Semi-Hard Cheese.

20.5.1 Pretreatment of Milk for Cheese:

• Fat standardization; make adjustments to specified fat/casein ratio (approximately the ratio which defines FDM% in the classification under 20.4.4 with allowance for salt).
• Pasteurization (see 11.2.1). Pasteurization is not always employed for hard cheeses; if not, the cheese must be kept for at least 60 days before consumption to ensure freedom from pathogenic bacteria.
• Cooling to renneting temperature, usually 30°.
• Transfer to cheese vat.

20.5.2 Optional Additives

• Calcium chloride (5-20 grams per 100 liters) to achieve constant coagulation time.
• Sodium or potassium nitrate (NaNO₃ or KNO₃) up to 0-30 grams per 100 liters of milk to prevent gas blowing of the cheese during fermentation. NOTE: IN MANY COUNTRIES THIS IS NO LONGER A PERMITTED ADDITIVE.
• Colouring agents (carotene or anatto) to eliminate seasonal variation in carotene content; or decolouring agents (green chlorophyll, a contrast dye) to obtain a pale colour in the finished cheese (e.g. blue-veined, mould ripened cheese).

20.5.3 Necessary Additives

• Starter. The starter culture is a very important factor in cheese making. Mesophilic cultures with optimum growth temperature of 20-35°C for cheese milk conditioned at moderate temperature (Cheddar, Gouda and Cottage cheeses) and thermophilic cultures for cheese milk conditioned at relatively high temperature (Emmenthal, Gruyere and Feta varieties). Mixed cultures are often used to achieve maximum aroma and flavour development. The criteria for the starter are: (a) ability to form lactic acid in a short time; (b) ability to cause proteolysis during ripening of the cheese; and ability to produce carbon dioxide for some cheese varieties.
• Rennet. Except for types of fresh cheese, such as cottage cheese and quarg, in which the milk is coagulated mainly by acid, all cheese manufacture depends upon formation of curd by the action of rennet or similar enzymes. The amount to be added depends upon the type of rennet available (liquid or powdered). Cheesemakers look for a constant coagulation time of approximately 30 minutes and make day-to-day adjustments to the amounts used.

• The first wire-frame cutters were meant for manual operation. However, similar designs are now made as attachments for mechanically operated cheese vats, where sturdy frames, with blades rather than wires, are attached to rotating arms which traverse the cheese vat at its length.

20.5.5 Whey Expulsion (Syneresis). The aim of cheese making is to obtain a curd with a defined moisture content. This is achieved by a controlled expulsion of whey from the curd particles. The cutting of the curd is done to facilitate whey expulsion by creating a much greater surface for drainage. Stirring of the curd also promotes whey drainage by the mechanical action and by preventing the particles from adhering to one another.

Pre-stirring. Immediately after cutting, the curd grains are very sensitive to mechanical treatment and the initial stirring must be gentle to avoid breaking the curd into "fines". However, agitation must be sufficient to prevent the grains from "matting" together into lumps. Curd made from skimmilk has a strong tendency to settle at the bottom of the vat and the stirring must be more intense than with full-fat cheese.

Pre-drainage of whey. For some varieties of cheese, it is practice to remove some of the whey from very full cheese vats so that hot water can be added for temperature adjustment. For each cheese variety, is important that the amount of whey - normally about 35%, sometimes as much as 50% of the batch volume- is kept consistent in the daily routine.

Heating/cooking/scalding. Heat treatment is required during cheese making to regulate the size and acid development of the curd. Heat causes contraction of the curd particles with increased expulsion of whey. More importantly, heat is used to regulate the growth of the lactic acid bacteria and control acid development in the curd. The time and temperature programme for heating is determined by the type of cheese and the method of heating (direct heating by adding hot water; indirect heating in a jacketed vat). Heating to temperatures above 40°C , sometimes called cooking , normally takes place in two stages

At 37-38°C the activity of the mesophilic lactic acid bacteria is retarded, and heating is interrupted to check the acidity by titration of the whey. Then, heating is continued to the desired final temperature. Above 44°C the mesophilic bacteria are totally deactivated, and they are killed if held at 52°C for periods of 10-20 min.

Heating beyond 44°C is typically called scalding. Some types of cheese, such as Emmenthal, Gruyere, Parmesan and Grana, are scalded at temperatures as high as 50-56°C. Only the most heat-resistant lactic-acid producing bacteria are can survive this treatment. Included is Propionibacterium Freudenreichii ssp. Shermanii, which is the prominent fermentation organism for the structure and aroma characteristics of these cheese varieties.

Final stirring. The sensitivity of the curd grains to mechanical action decreases as heating and stirring continues. More whey is excluded from the grains during the final stirring period, primarily due to continuos development of lactic acid, but also by the mechanical effect of stirring. The duration of final stirring depends upon the cheese variety and is dictated by the desired moisture content.

Final removal of whey. As soon as the required acidity of whey and firmness of the curd have been attained the residual whey is drained off in various ways.

20.5.6 Final treatment of curd. The curd can be treated in several ways after all the free whey has been drained away. It can be:

Transferred directly to moulds (granular textured cheeses) and pressed.

Pre-pressed into a slab and cut into pieces of suitable size for placing into moulds (round-eyed cheeses) for final pressing.

Exposed to a cheddaring process, the last phase of which includes milling into chips which can be dry-salted and either hooped or, if intended for Pasta Filata types of cheese, transferred unsalted to a cooking-stretching machine.

20.5.7 Pressing For pressing into the desired shape and removal of residual whey, the curd blocks are wrapped in cheese cloth and placed in a suitable cheese mould and pressed for some hours. The amount of pressure and the length of time varies with the type of cheese.

20.5.8 Salting. Salting takes place after the cheese has been pressed, often starting the following day. In cheese as in many other foods, salt normally functions as a condiment. However, salt has other important effects, such as retarding starter activity and microbial processes associated with cheese ripening. Application of salt to the cheese block causes more moisture to be expelled, both through osmotic effects and a salting effect on the proteins. With few exceptions, the salt content of cheese is 0.5-2%. Blue cheese and Feta cheese, however, have a salt content of 3-7%. The exchange of calcium for sodium in paracaseinate has a favourable influence on the consistency of the cheese, which becomes smoother.

20.8.1 Preparation of Common Brine Solutions. Brine is made by dissolving salt (sodium chloride) in water or sometimes whey. The difference in osmotic pressure between brine and cheese causes some moisture to be expelled with its dissolved components, including whey proteins, lactic acid and minerals , in exchange for NaCl. The use of whey minimizes the concentration differences for the dissolved milk constituents but makes it more difficult to control the salt concentration by density measurements. Brine is kept in continuos use over weeks and months but the salt concentration must be replenished each day. Aside from the loss of salt by penetration into the cheese, an equilibrium state will eventually be attained by the dissolved whey constituents and by pH. For this reason, "old" whey is considered best for development of the proper cheese quality, both flavor and texture.

20.8.2 Salt Concentration. The desired salt concentration is maintained by daily measurements of the density of the brine using a hydrometer (°Be) or by using a refractometer calibrated for the brine composition. The following table shows the composition of salt/water solutions. Note the differences between expressing salt concentrations as weight-by-weight and weight-by-volume. The difference occurs because the volume of the solutions is increased by salt addition, but only by 0.33-0.36 liters per kilogram of salt.

20.8.2.1 Density versus Salt Concentration

20.8.2.2 Calculation of Brine Volume

20.8.2.5 Measuring Salt Concentration by Hydrometer. Hydrometer readings may be expressed as degree Baume (°BE). The instrument is calibrated for densities between 1.00 (0°Be) and 1.842 (66°Be). The equation on the right will convert Baume readings to density:

20.9 Salt Penetration in Cheese. The Dairy Processing Handbook cites the following information from the Danish Dairy Research Institute (Report No. 22).

Cheese curd is criss-crossed by capillaries; approximately 10,000 per cc. have been found. There are several factors that can affect the permeability of the capillaries and the ability of the salt solution to flow through them, e.g. since fat globules may block some of the capillaries, salt penetration will be delayed in cheese of high fat content.

The pH at the time of salting has considerable influence on the rate of salt absorption. More salt can be absorbed at low pH than at higher pH. However at low pH (<5.0), the body of the cheese is hard and brittle. At higher pH (>5.6), the body remains elastic.

The loosely bound calcium is sensitive to pH changes; the lower the pH the more calcium will leave the paracasein complex as hydrogen ions protonate the calcium sites. At salting these sites will not engage in exchange with sodium ions. Exchange takes place between sodium and calcium but not with the hydrogen ions.

If the pH of cheese curd before salting is in the high range (6.0-5.8), a considerable amount of calcium is still present in the paracaeinate. On brine treatment too much sodium will become attached to the casein through exchange with some of the calcium. This results in a softer cheese which may even lose its shape during ripening.

At the pH range 5.2-5.6 there is a balance between the calcium ions and hydrogen ions to bind the optimum amount of sodium to provide for a satisfactory body and texture.

At low pH (<5.2), too many sites are protonated and the sodium exchange becomes too small; therefore the body and texture of the cheese becomes too hard and brittle.

The higher the salt concentration of the brine, the more salt will be absorbed. At low concentrations (<16%), the paracasein swells and the surface will be smeary and slimy as the result of partial resolubilization. It is common to use salt concentrations near the saturation point (23%) at 10-14°C.

20.10 Ripening of Cheese. With the exception of fresh cheese, all other cheese varieties go through a series of ripening processes involving microbiological, biochemical and physical changes to the product.

20.10.1 Lactose Decomposition. The moisture remaining in the curd after whey draining has the composition of the whey -- or diluted whey -- if water has been added for temperature adjustments. Lactose fermentation should be controlled in such a way that all lactose has disappeared no later than after pressing and prior to brine salting.

The lactic acid which is produced is neutralized to a great extent in the cheese by the buffering components of the milk many of which are included in the coagulum. Lactic acid is thus present as lactates in the completed cheese. At a later stage , the lactates can provide substrate for the propionic bacteria which are an important part of the microbiological flora of Swiss cheese, including Emmenthal, Gruyere and similar types.

• "Eye" Formation. In the section on ice cream we discussed the growth of ice crystals as an event where the big "fish " feed on the small ones and, in the process the big ones get larger while the small ones disappear. The very same situation occurs in cheese with holes. The "eyes" of many cheese varieties are formed from carbon dioxide evolving from microbial action in the manner shown below. Some starter organisms, particularly mixed cultures containingLeuconostoc citrovorum, produce carbon dioxide from fermentation of citrate. Here, the large gas bubbles feed on the smaller ones, because the gas pressure in the small bubbles is higher than in the bigger ones as a result of the surface tension which drives the gas toward the bigger holes. Such "eyes" are a desirable characteristic in some cheese but their size or number should not be excessive.

• Undesirable Gas Formation. If milk for cheese is contaminated with coliform bacteria (hetero fermenters of lactose) excessive gas formation may occur which affects the cheese structure and also flavour and aroma. Strict sanitation and hygiene as well as heat treatment of milk will control this cheese defect.

• When butyric acid fermentation occurs, gas pressure builds up within the cheese; the structure becomes disrupted by holes and cracks; the entire cheese swells and may eventually rupture ("blowing"). The responsible organism Clostridium tyrobutyricum is not a pathogen, but nevertheless, a serious quality menace. This anaerobic bacteria does not grow well in milk but may thrive in the anaerobic environment within large cheese blocks. The invasion of C. tyrobutyricum into milk originates at the milking barn by way of the fodder (silage), but also frequently at the cheese factory. The use of wooden cheese vats and utensils may be implicated, because these may harbor the spores. The spores of C. tyrobutyricum are not destroyed by heat treatment of milk and the only effective remedy is to add sodium or potassium nitrate which elevates the oxygen tension and inhibit their growth. NOTE: nitrates are not a permitted additive to cheese milk in some countries.

20.10.2 Protein Decomposition. The ripening of cheese is characterized by extensive proteolysis. The degree of protein decomposition affects the quality of the cheese in profound ways, particularly flavor and aroma but also body and texture. The changes are brought about by the enzyme systems of

• Rennet
• Microorganisms
• Native proteases in milk (plasmin)

Rennet is a proteolytic enzyme which coagulates milk by cleaving a specific bond in kappa-casein. However, prolonged action of rennet causes breakdown of paracasein into polypeptides. This attack serves as a preconditioning treatment for the subsequent action of the bacterial enzymes which decompose polypeptides faster than the intact paracasein. In cheese varieties, such as Swiss cheese, where the curd has been deliberately scalded, rennet has been destroyed, but the native proteases in milk can also hydrolyze paracasein into polypeptides, although at a slower rate.

20.10.3 Fat Decomposition. A number of mould-ripened cheese varieties, notably Camembert; Brie; Roquefort; and Stilton are characterized by extensive lipolysis.

Such cheese often have pronounced flavour and aroma from both proteolysis and lipolysis and the consumers are people who have acquired a taste for the exotic.

• Camembert and Brie are manufactured as high-fat products in small shapes of a size no more than 1/2 kilogramme. During ripening, growth of a white mould (Penicilium camemberti) is encouraged on the surface. This aerobic organism produces both proteases and lipases which penetrate below the surface into the cheese. The initial fermentation takes place at relatively high temperatures( 35-38°C) at high humidity and over a short time sufficient to cause a dense surface growth. The cheese is then cooled, packaged and marketed, often before it is fully ripe. Experienced consumers have learned to evaluate when such cheese has reached maturity by the proper softness at the surface with a remaining firmer core. Fully ripened Camembert or Brie cheese is characterized by a mild aroma and a soft, spreadable consistency. An overripe cheese will begin to smell of ammonia and volatile fatty acids.
• Roquefort and Stilton cheeses are also high-fat varieties; in this case ripened by green moulds (Penicilium roqueforti). The typical shape is that of a cylinder of a size between 3-5 kg. The milk is often homogenized to give a large surface area to the fat. Mould cultures are added to the milk before coagulation and the cheese blocks are salted in concentrated brine to slow acid development.

20.11 Study Questions.

1. What are the minimum utensils needed for making cheese in a cottage industry?
2. What are the three characteristics used for classification of cheese by the Codex Alimentarius?
3. What necessary additives are needed in cheese making?
4. What are the optional additives?
5. Describe how a cheese maker may determine when the coagulum is ready for cutting.
6. What is the purpose of immersing salting cheese in a brine solution?
7. Explain why the density of brine solutions, measured in Baume degrees (°Be) by a hydrometer, is not exactly the same as the density obtained by gravimetric measurements.
8. What happens to the milk calcium during cheese making?
9. What are the changes to cheese curd during brine salting?
10. What happens to lactose during the different stages of cheese making?
11. What other biochemical changes may be expected during cheese making?
12. How is mould development controlled in ripening of "Blue cheese"