Cheese technology

Overview

Cheese results from the selective concentration of milk. The water is removed in varying proportions depending on the variety, bringing with it some of the soluble and coagulated proteins. The water retained in the cheese plays an important role. For microorganisms, it influences its rate according to the speed of fermentation and maturation, shelf life, texture, while contributing to performance. Fat affects the texture, flavor, yield and some color. Lactose acts as a substrate for the formation of acid and its effects on the coagulation of milk, draining and texture of the curd as well as the growth of microorganisms. As for the casein which, in coagulating, forms the basis of cheese paste, and its degradation contributes to generate a variety of flavors. For their part, the serum proteins retained in the curd contribute to its nutritional value while playing a role in refining. In turn the minerals involved in the coagulation of milk and affect the drainage and texture of cheese.

The cheese is mainly in two stages: the curdling, or coagulation, milk and dehydration of coagulum. For some cheeses, we must have recourse to a third stage of refinement, during which the action of microorganisms and enzymes make the appropriate changes according to varieties.

Coagulation of milk

Two methods are used to curdle milk for cheese: acidification and rennet added, giving rise to two types of curd or acid curd and curd rennet. The properties and behavior of each differ significantly, so that their differences are the basis of technology and characteristics of various types of cheese.

Coagulation by acidification

Coagulation of casein by acidification (fermentation) result from the loss of its electric charge to its isoelectric point (pH 4.6). The lowering of pH by acidification (H⁺ion) reduces to its neutralization of the negative ionization of casein micelles. PH 5.2 (at 20 ° C) they become unstable enough to form a beginning of agglomeration, while at pH 4.6, the electrical charge is completely void, resulting in their complete coagulation.

At the same time, the acidity of the medium has the effect of increasing the solubility of minerals such as calcium and phosphorus of the organic micelle gradually pass into solution in the aqueous phase. There is therefore a partially demineralized curd leaving easily cross the whey.

The coagulum obtained by acidification of this chemical and physical properties that must be taken into account in making cheese. Thus, although a certain firmness, it is porous, brittle and unable to contract: what makes her stronger difficult, especially since it does not lend itself to mechanical treatments.

Coagulation by acidification technique is regular in the case of fresh cheeses such as cottage. Milk at rest becomes a homogeneous gel under the effect of the gradual increase in the acidity of lactic cultures. We choose the inoculation rate and temperature of fermentation to achieve, at will, or coagulation hasty or slow. It is important that the milk is apt to ferment, free of antibiotics and inhibitor agent, and that culture should be active.

For some varieties of cheese, it starts a sudden coagulation by adding acid directly to milk that it heats up then. In this way, however, does not a homogeneous coagulum, but a flaky precipitate. This process allows to recover, in addition to casein, whey protein clottable by heat in acid medium.

Rennet coagulation

In cheese, it appealed more to the rennet coagulation. They are, in this case, add milk enzyme which owns the complex coagulate casein. Expressed in summary, is the phenomenon where the phosphocaseinate calcium soluble in the milk is transformed under the action of a coagulant enzyme, in phosphoparacaséinate calcium, insoluble. It is important to note that the rennet curd is not demineralized acid as the curd is the fundamental difference between the two. Calcium in particular, as well as phosphorus, play an important role in the clotting mechanism and remain components of the casein gel. This gives it special properties: it is compact, flexible, elastic, waterproof and contractile. These traits are reflected primarily in the draining and firming of the curd and make it able to withstand mechanical during manufacture.

Rennet

Rennet is an enzyme secreted by the gastric mucosa of the fourth stomach (abomasum) of young calves (also venison and lamb), before weaning. This secretion is the state of inactive precursor, the proprésure which, in a neutral, has no enzymatic activity, but quickly became active rennet in acidic media. Rennet contains, in fact, two enzymes: chymosin as principal constituent, and pepsin. At weaning, pepsin is highly dominant, whereas the production of stops chymosin. We extract of rennet rennet by soaking them in brine.

However, it is the origin of microbial rennet which is increasingly replacing calf rennet. They are prepared by extracting the enzymes coagulantes that secrete certain microorganisms. The most satisfactory are molds of the genus Mucor. Some of these enzymes are stable to heat greater than the coagulants of animal origin.

The commercial rennet preparations are determined to have a fixed capacity coagulant called "force". The strength of the rennet is generally expressed as the ratio between the volume of milk coagulated by rennet volume under specified conditions.

The proteolytic activity of rennet is mainly on the casein and to a lesser extent, other proteins. It plays two main roles. The first is to cause the destabilization of casein micelles by attacking the k-casein to a specific place of its molecule, the peptide bond between an amino acid called phenylalanine and neighboring amino acid, a methionine, which is called link-MET PHE. We usually judge the strength of a rennet efficiency by cutting the link peptide, which will cause the coagulation of milk. There is more than 164 other peptide bonds may be cut on the k-casein, in addition to those existing in other parts of the micelle.

The second role of rennet is to address these links in order of specificity characteristic of the enzyme used. Celte secondary action of the protein slowly during manufacture, after clotting, and will continue during the ripening of cheese. The nature of these developments coupled with the activity of native milk proteases, proteases of the original flora of milk and of the closing, will give the cheese its specific characteristics of texture and flavor.

Influence of certain factors in the rennet coagulation

Changes in rennet coagulation depends on a number of factors including the amount of rennet used. In similar conditions, the dose is proportional influence the speed of coagulation and rheological properties (firmness) of curd.

The temperature also plays an important role in this phenomenon. A temperature of 40 ° C to 42 ° C is ideal for rennet coagulation, whereas at temperatures below 10 ° C and above 65 ° C, it does not happen coagulation. Expressed in relative terms, the clotting time, based on 1.0 for a temperature of 40 ° -42 ° C, will be about 1.4 to 30 ° C and 2.0 to 50 ° C. The temperature has an influence on the global phenomenon of coagulation, but to different degrees on each of its two phases. The primary phase, including the enzymatic action on the k-casein occurs even at temperatures below 10 ° C, while the secondary phase, more sensitive, requires higher temperatures to achieve coagulation itself. This behavior allows us to cold boot the primary phase by submitting emprésuré milk at a temperature below 10 ° C, it did not quail, then after a few hours to do so instantly coagulate quickly reheating over 20 ° C. This is the principle underlying the renneting cold coagulation or continuously.

The pH changes the speed of clotting and curd firmness. Alkaline, rennet is inactivated and does not therefore coagulation. For against, the lower pH favors the action of rennet on casein, as the acidity decreases the stability by reducing its electrical charges. The optimal pH for the activity of rennet is 5.5. Under identical conditions, the average duration of coagulation will be 200 seconds at pH 6,6-6,7, 50 seconds at pH 6.1 and 30 seconds at pH 5.7. It is important to note that the coagulum obtained under the joint action of rennet and acidification of a character different from purely rennet curd.

The concentration of Ca^{+ +} ions is also an important factor, it did not affect the enzymatic phase, but only on the secondary phase, that of coagulation itself. Containing abnormally low results in a slow clotting and a soft curd. The fix in this case is to add calcium chloride (CaCl₂) to milk.

For its part, the content of colloidal calcium phosphate in the process of coagulation, is mainly responsible for the tension of the gel.

Coagulation Joint

For most cheeses, it causes the curdling of milk by the combined action of rennet and acidification with usually a predominance of one or another of them. This provides mixed coagulation properties intermediate curdled less features than curdled obtained by a single mode coagulation. The respective participation of rennet and acidification may vary at will according to the types of cheese.

Renneting of milk more or less acidic, and acidification of a rennet gel are applications of coagulation mixed. It may be noted, inter alia, that in the first case, the acidity decreases the time of rennet coagulation, and in the second, that the rennet gel undergoes a progressive demineralization.

Draining of the curd

The cheeses are concentrated milk. The concentration is achieved by expelling more or less thrust of water and soluble components. The resulting dough is formed mainly of casein and the fat that adheres physically. For its part, the whey expelled causes most of the lactose and non-coagulated nitrogen and a variable proportion of minerals.

Basically, the more or less of serum used in the curd which will trigger and determine several characteristics that differentiate the varieties of cheese firmness, texture, intensity and speed of maturation, and so on. That is why manufacturing techniques made for drainage are of great importance, especially since it is through their control of cheese varieties meet the standards required for their total solids.

Freezing fresh, original acid or rennet, is unstable. More or less rapidly, whey trapped tend to withdraw and to separate the curd, who is thus to decrease volume. This is the phenomenon of synérèse. The term refers to drainage throughout the synérèse and evacuation of whey, including additional drainage at the molding, pressing until the time of ripening.

Draining occurs differently depending on whether one is dealing with a curd or an acid curd rennet, and the resulting pulps have different characters.

History of drainage: the case of acid curd

The coagulum obtained exclusively by acidification no longer structured micelles. It consists of demineralized casein molecules, without ties or cohesion and unable to contract. The water is chemically bound to the solid phase and is used heavily. In a fresh coagulum, the start of synérèse itself spontaneously and rapidly, releasing the serum readily crosses the porous mass. But the phenomenon does not occur to an advanced degree, but left a little dehydrated curd and humid. Especially moreover, that such fragile and brittle, the curd acid is not susceptible to mechanical work. The techniques of this kind which are needed in cheese, such as mixing, must be applied in a manner sensitive, otherwise it will loose, excess, small curd particles or "fines", which makes the trouble and whitish whey while causing losses.

In the work of acid curd, is generally used to heat as a means to supplement the lack of physical effect to the consolidation, the rise in temperature promotes, in fact, a more intense and draining faster.

History of drainage: the case of rennet curd

The different nature of rennet curd affects the behavior of the drain. During coagulation, the casein micelle structure and retains its link calcium and phosphorus as major elements, among others, gives it its strength, its cohesion and impermeability. Under the effect of rennet, it occurs to new routes. Several micelles connect them to form networks in which the expanded mesh inclusive, such as a spongy tissue, mechanically retain much of the water. The interaction of all these phenomena leads to the network and closer to contract
making possible the removal of serum.

However synérèse does not spontaneously. The coagulum waterproof makes it difficult and slow the passage of serum. But because of its cohesion, it is able to withstand mechanical favorable to its development. Meanwhile, the temperature and pH of the environment also have an impact on drainage. It is through the combined action of all these means we can control the speed and degree of hardening of the curd. To this end, we operate the following:

1. Cutting: This operation is to cut into portions equal the mass of clotted milk. It is also called "draining" This will increase the total surface exudation of serum and promote drainage. In principle, fresh cheeses and soft cheeses, the curd is cut into cubes bigger, while the firm cheeses are cut smaller. Research on an optimum size for stronger manner.
2. Brewing: The mechanical agitation of the grains of curd in the whey has the effect of preventing their agglomeration and accelerate dehydration. It must be conducted so as to prevent breakage of the grains of curd and thus cause losses. It must be small with fragile coagulum obtained by acid coagulation. As against the required curdled rennet for cheese farms can support a more vigorous agitation and more continuous.
3. Pressing: This process allows to extract free water from the dough and cheese to complement its draining. Obviously, it does not apply to all types of cheese, but only those whose structure is able to withstand direct pressure. It goes without saying that the conditions of pressing, such as intensity, duration and progression depend on the nature of cheese and must adapt.
4. Temperature: This is by activating the reactions of rennet and by reducing the viscosity of the coagulum that elevated temperature promotes the contraction of the gel and hence the removal of serum. The degree of heating or cooking, varies with the type of curd, acidity and firmness desired cheese. One can even reach temperatures of 550-600C in the manufacture of cheese farms, low acidity, such as Gruyère-type as well as in the case of Italian cheeses, pasta plastic.
5. Acidity: The acidification of the rennet gel causes a decrease in the water of hydration of micelles, partially soluble salts of calcium increasing the permeability of coagulum accelerates secondary connections to ensure its contraction all these conditions account for facilitate and accelerate the expulsion of whey. The effectiveness of acidification on the drain is hardly noticeable to pH 5.5 but then increases to pH 4.9 where it reaches its maximum. Acidification regulates the calcium-phosphorus Association to give the cheese its elasticity and fermented.
6. Other factors: The drain is connected to the tension of the curd: In general, the clotting time is short, the stronger will be the tension of the curd and the best drip. Anything that causes a soft curd night indirectly draining. Thus may be involved: the amount of rennet and total proteolytic activity, poverty milk minerals, especially calcium, as well as soluble proteins denatured by severe heat. It is also noticeable that a higher fat content makes the distribution of serum more difficult through the gel and thus strengthening its slower.

History of drainage: the case of curd mixed

The coagulum mixed characters are intermediate between purely curdled rennet or acid. The draining takes place in various ways according to the predominance of one or the other coagulant agent. The rennet curd retains its ability to strengthen even though demineralize during acidification. Meanwhile, the acidity developed active synérèse. In fact, there is an interaction of all factors involved Draining is done more or less thrust controlled by the interaction of the role of rennet, acidification, modalities for cutting, mixing , cooking and pressing. We come to obtain cheeses with their specific properties.

Cheese

Most cheeses do not eat fresh, but after undergoing a maturation or ripening. This is a biochemical transformation, gradual and more or less extensive, constituents of the cheese in many products more soluble responsible for new tastes and physical changes of pulp, as the creamy texture, the presence of openings or "eye "or the formation of crust on the surface.

The ripening process is complex due to the involvement of many parameters. This situation is primarily linked to the already complex nature of the substrate, the curd composition and structure of its constituents, such as water content and degree of dispersion, the structure of casein, etc.. It is also due to the variety of officers and refining their methods depending on the reaction conditions.

The degradation of organic cheese (maturing) is through the combined action of enzymes and variable and the microbial flora.

Action of enzymes

The natural enzymes of milk, including lipases and proteases involved in maturation but is slow and hardly noticeable. Is that the conditions of refining does not contribute: the temperature is lower and the pH more acidic than their optimal zones. Partly destroyed by pasteurization, the effect is all declined. However, during a prolonged maturation, we can see a degree of refinement more pronounced in cheese and milk preheated than pasteurized milk. The enzymes of rennet added to milk in order to exert its coagulation proteolytic action and more action coagulant.

In soft cheeses, the participation of the rennet is low because, first, that the ripening period is short and on the other hand, proteases secreted by the flora of cheese are very active. His role seems more important in the pressed cheeses, uncooked, such as Cheddar.

Action of the microbial flora

These are microorganisms that play a role in the maturation of cheese. For more details, remember that they are acting, in fact, through the enzymes they secrete. The diversity of flora, its evolution during refining as well as changes in the substrate, making it difficult to study the role of a particular microorganism.