It's a shame, but it happens in cheese making. Maasdam has a sweet-nutty flavor and shouldn't be bitter. But making cheese is a complex biochemical process, and the result is not always predictable, I found it on the Internet about the bitter taste of cheese. I had it at the initial stages, when I used meito as a starter, now I have given it up. But the reasons can be different
Bitter taste is the most common vice of rennet cheeses with low heating temperatures. II. It is rarely found in large cheeses due to the peculiarities of proteolysis in these cheeses. In accordance with GOST “Hard rennet cheeses. Specifications ”cheeses with light bitterness are rated for taste and smell by 37-39 points out of 45, which leaves them in the highest grade in this indicator; cheeses with pronounced bitterness are estimated at 30-36 points, that is, they are classified as grade I or rejected.
Substances that give bitterness to cheeses can get into cheese with milk, mineral additives (NaCl, CaCl2, KNO3) or form in cheese when casein breaks down.
The bitter taste of milk when leaving the udder is most often due to the presence of bitter wild-growing herbs in the feed: wormwood, buttercup, colza, caustic warbler, mustard, wild onion and garlic, lupine, tansy, chamomile, hellebore, ivy, yarrow, sweet clover. The bitterness in these herbs is due to glucosides, essential oils that are not destroyed by the cow's body. During the production of cheese, they are concentrated in the protein and lipid phases of the cheese, so the bitterness caused by them becomes more pronounced in cheeses than in the original milk.
Bitterness in milk can occur when lactating cows are fed large quantities of raw potatoes, turnips, rotten beets, rutabagas, beet tops, but it is not known whether or not this bitterness is transmitted to cheeses. Bitterness due to the presence of bitter substances in milk is found in the cheese immediately after production and does not progress as it matures.It cannot be eliminated by technological methods.
Bitter substances, mainly magnesium salts, can get into cheese with salt and low quality calcium chloride. High doses of CaCl2 increase the risk of this type of bitterness. Large doses of saltpeter can also cause bitterness in cheeses. The most common causes of bitterness in cheeses are hydrophobic peptides with a molecular weight of less than 1400. In cheeses, they are formed by the breakdown of casein by rennet and other milk-clotting enzymes, sourdough lactococcus and foreign microflora. Rennet in cheese forms bitter peptides from α-casein. Other milk-clotting enzymes probably form bitter peptides in cheese and from β-casein. Bitterness is more common in cheeses made with these enzymes than in cheeses with rennet. Lactococci form bitter peptides from æ- and, mainly, from β-casein using proteinases localized on the cell wall and exopeptidases; Prt - mutants of lactococci that do not form exopeptidases, do not form bitter peptides.
Bitter peptides are formed during production, which is apparently due to the most favorable conditions for the action of proteinases at this stage. However, in fresh cheeses, bitterness due to bitter peptides does not appear. Perhaps the concentration of bitter peptides in cheeses of this age is not high enough. As the cheese ripens, the content of peptides with a molecular weight of less than 1400 in cheeses increases: in cheeses of 3 months of age, their content in relation to the content of total nitrogen increased by 1.49 times in comparison with 1-month-old cheeses, but in cheeses of 6 months of age by compared with cheeses of 3 months of age - only 1.19 times. The sum of these peptides, formed separately by rennet and the microflora of the starter culture, in cheeses of 1 and 3 months of age was 3 and 2 times lower than their amount with the combined action of these factors.
Apparently, all lactococci, upon splitting caseins, form bitter peptides, but the strains that form bitterness in cheeses (“bitter” strains) form them in large quantities and in a wider range of physicochemical environmental conditions than strains that do not form bitterness ( "Non-bitter" strains). Bitterness in the cheese is formed only by those strains whose biomass at the end of pressing exceeds 10 in 9 CFU / g, ie, the so-called "fast" strains. Proteinases of "non-bitter" strains are inactive at heating temperatures of more than 38 ° C; the rate of reproduction of "non-bitter" strains during production is lower than that of "bitter" strains, and the number of their viable cells in cheeses after pressing is usually less than 10 in 9 CFU / g. It follows from this that the most favorable conditions for the formation of bitter peptides or their precursors from casein are created during the production of cheese. Lactococcal strains that multiply relatively slowly at this stage of production usually do not form bitterness in cheeses. These strains, in comparison with the "fast" ones, have a low proteinase activity, which, apparently, is the reason for their slow growth in milk. It would seem that to prevent the appearance of bitterness in cheeses in sourdoughs, only "slow" strains of lactococci should be used, however, the low rate of reproduction of the microflora of the sourdough during production creates favorable conditions for the reproduction of technically harmful and pathogenic microflora, reduces the severity of the taste of cheese. The mass of bitter peptides formed in cheese by milk-clotting enzymes increases as the amount of enzymes remaining in the cheese increases. The amount of rennin and possibly pepsins remaining in the cheese mass increases in proportion to the acidity of the whey at the end of the grain processing. The amount of microbial milk-clotting enzymes in cheese does not depend on the acidity of the whey.
Bitter peptides in mature cheeses are mainly β-casein fragments, i.e. they are formed by the microflora of the starter culture, although milk-clotting enzymes form more peptides with a molecular weight of less than 1400.This is due to the fact that lactococcus starter culture with the help of intracellular proteinases destroy bitter peptides formed by milk-clotting enzymes from α-casein, but do not destroy those that form themselves from β-casein. The rate of cleavage of bitter peptides by lactococci decreases with decreasing pH and temperature of cheese ripening. Peptidases of "non-bitter" strains break down bitter peptides at a pH greater than 4.5, ie, at any pH of hard cheeses; "Bitter" strains - at a pH not lower than 5.5. Cheeses with low pH and low ripening temperatures almost always taste bitter. "Non-bitter" strains of lactococci form significantly more CAA in cheeses than "bitter" ones, which indicates more active cleavage of peptides by them. High acidity in cheese can cause bitterness not only due to inhibition of the breakdown of bitter peptides by the microflora of the starter culture, but also because calcium lactates themselves have a bitter taste.
The emergence of peptide bitterness is facilitated by the processing of rennet milk, milk with a high content of somatic cells, pasteurized at temperatures above 76 ° C. A common property of such milk is a low syneresis rate, which leads to the production of cheeses with high humidity, and the result is a low pH of the cheeses. In addition, when processing such milk to improve its rennet clotting and the rate of drying of grain, the doses of milk-clotting enzymes and CaCl2 are often increased, which contributes to the appearance of bitterness in the cheese. These measures cannot improve the technological properties of milk, since its defects are associated with a deficiency of casein or with the blocking of æ-casein by denatured heat treatment with β-lactoglobulin. Rennet milk, milk with a high content of somatic cells cannot be used to make cheese. Milk, pasteurized at elevated temperatures, can be used to make cheese only with a radical modification of the technology.
The reason for the bitterness in cheeses can be the high initial acidity of the milk, which also leads to a decrease in the pH of the cheese, since with a high acidity of the whey during the production of cheese, the cheese mass loses a lot of Ca and P, which reduces its buffering capacity, and retains more lactose and lactic acid. which increases the total acid content of the cheese.
Bitterness in cheeses depends to a large extent on the cheese making process, and above all on the rate at which acidity builds up. Too high a rate of acidification lowers the pH of the cheese for the above reasons. It can be caused not only by the processing of milk with high acidity, but also by high doses of starter culture, contamination of lactococcal starter culture with lactobacilli, low heating temperatures II, prolonged processing of grain. To some extent, the decrease in the pH of the cheese due to the high rate of acidification during production can be reduced by diluting the whey with water, but this simultaneously reduces the rate of syneresis and reduces the expression of the cheese flavor.
The factors responsible for the high rate of acid formation during production simultaneously increase the biomass of the microflora of the starter cultures in the cheese at the end of production, which, regardless of the pH, increases the risk of sour taste. The best way to regulate the rate of acid formation is to change the dose of starter culture and heating temperature II, the latter must be kept, if possible, at the maximum permissible level. The low acid production rate can also cause a drop in pH and a bitter taste in cheeses, as in this case the fermentation of lactose in the cheese is delayed, and all the acid formed by lactic acid bacteria during the fermentation of lactose after the cheese is made remains in the cheese. In this case, the minimum pH level in the cheese occurs later than usual.In addition, the low rate of acid formation during the production of cheese creates more favorable conditions for the growth of extraneous microflora, which can form bitter peptides and reduce the safety indicators of the product. Thus, maintaining the rate of acid formation during cheese production at an optimal level is a necessary condition for preventing bitterness in cheeses and producing high quality cheese in other respects.
The main reasons for the low rate of acid formation in the production of cheese are the use of unripe milk, milk containing inhibitors of the growth of the ferment microflora, a low dose of ferment, high heating temperatures of II, a high degree of salting in the grain, and most importantly, the action of a bacteriophage. In the latter case, bitterness in cheeses is unlikely to appear, since the bacteriophage, causing lysis of the cells of the microflora of starter cultures, on the one hand, limits the ability of this microflora to produce bitter peptides, on the other hand, it intensifies the cleavage of bitter peptides formed by lactic-coagulating enzymes due to the release of intracellular proteinases lactic acid.
A slow increase in acidity during cheese production, such as processing unripe milk, reduces the rate of syneresis and increases the moisture content of the cheese. To accelerate the syneresis, in this case, the dose of the starter is increased, the salting in the grain is reduced or completely canceled. At a normal rate of syneresis, salting in the grain helps to develop cheese with an optimal moisture content after pressing; at a low rate of syneresis, it negatively affects the product.
The intensity of salting has a great influence on the formation of bitter peptides in cheeses. Salt has a small effect on the primary stage of αs1-casein hydrolysis - the cleavage of αs1-I peptide from it by milk-clotting enzymes, while the subsequent hydrolysis of αs1-I peptide strongly depends on the salt content in the aqueous phase of the cheese. Salt inhibits β-casein hydrolysis to a large extent. The taste threshold of some bitter peptides from β-casein (0.004 mM) is very low. It would seem that for cheeses salted in brine, the degree of salting cannot have a significant effect on the formation of bitter peptides, since salt slowly spreads inside the cheese head. However, the microflora of the starter culture begins to more or less actively break down β-casein 30 days after production, when the salt has already been sufficiently pro-cycle deep into the head. It is believed that bitterness is rarely found in cheeses containing more than 4.9% salt in the aqueous phase (2% or more in cheese).
The degree of danger of bitterness in cheeses depends on the species and strain composition of the starter cultures. The starter culture should not include "bitter" strains of lactococci. It should contain a sufficient number of diacetyl lactococcus or leukonostok cells with low proteinase activity and a high ability to break down bitter peptides. According to Stadhouders, about 20% of the strains with high proteinase and acid-forming activity are sufficient to obtain cheese without bitterness in the sourdough. A cheese manufacturer must purchase starter cultures from a firm that consistently produces products that pose a minimal threat to the formation of bitter peptides, provided the remaining starter requirements are met.
The same must be said about preparations of milk-clotting enzymes, whose ability to form bitterness depends on the degree of their purification. Bitterness in cheeses can occur when processing milk containing more than 10 6 CFU / ml of psychrotrophs. The psychrotrophic bacteria themselves die during pasteurization, and their proteolytic and lipolytic enzymes partially retain their activity and cause taste and odor defects.
Previously, one of the main reasons for the appearance of bitterness was considered to be the reproduction of mammococci in cheeses (according to the modern nomenclature Ent faecalis subsp. Liquefaciens). This species can cause bitterness in cheese with massive colonization of milk with enterococci and low activity of the microflora of the starter culture.Milk with a high content of enterococci is not suitable for the production of cheese due to its total bacterial content. Enterococci can cause defects in cheese if pasteurized milk is stored at temperatures above 7 ° C or if it is matured without the addition of starter culture.
Bitterness in cheeses can also be caused by other representatives of extraneous microflora, for example, psychrotrophic strains of enterobacteria, but they can multiply in cheese to a dangerous level only if the milk pasteurization regime is violated and the leavening activity is low.
Thus, there are many reasons for the bitter taste in small cheeses, making this the most common flaw. Essentially, the absence of bitterness in cheeses can only be guaranteed if all the requirements for cheese production are met. The main attention should be paid to the rate of acid formation during the production of cheese, which should not be too high and not too low (the optimal rate of acid formation is estimated by the increase in whey acidity, the pH of the cheese after pressing and the minimum pH of the cheese), obtaining cheese with optimal moisture, the use of preparations CaCl2, NaCl and milk-clotting enzymes of appropriate purity, strict control of doses of CaCl2, saltpeter, milk-clotting enzymes, establishing the salt content in the aqueous phase of small cheeses in the range from 4.9 to 5.7%, the use of high-quality starter cultures and milk-clotting preparations, maturation with adequate temperature.
