CHAPTER XIV

CHEDDAR CHEESE RIPENING

Freshly made Cheddar cheese is hard, tough and elastic and lacks characteristic cheese flavor. In this condition it is called "green," unripe or not cured. Before the cheese is ready to be eaten, it passes through a complex series of changes which are collectively known as ripening. In the ripening process the texture becomes soft and mellow and the characteristic cheese flavors develop. Cheese ripening must be considered from two view-points, first, the changes taking place inside the cheese and secondly the outside conditions necessary for ripening. Some of the chemical changes during ripening are known, while others are not understood. The different agents causing ripening, and the constituents of the milk, will be discussed.

231. Fat.—Numerous investigations have been made to ascertain what chemical changes the fat undergoes in the ripening process. Suzuki,[103] in studying the fat, found no enzyme capable of producing lactic acid or volatile fatty acids. However, these acids were found in increasing amounts during the ripening process and after the lactose had disappeared. Acetic and propionic acids reached a maximum at three months and then decreased, while butyric and caproic acids continually increased during the experimental period covered. Formic acid was detected in the whole-milk cheese only at the five and one-half month stage. In the judgment of the experimenter the principal source of acetic and propionic acids was probably lactates. Traces of these acids may have had their origin in protein decomposition or further fermentation of glycerine. The principal sources indicated for butyric and caproic acids were fats and proteins.

The distillate from the experimental cheese was designated "flavor solution" and contained alcohols and esters, giving a close resemblance to the cheese aroma. The "flavor solution" from the mild whole-milk cheese contained esters made up largely of ethyl alcohol and acetic acid, while from the more pungent skimmed-milk cheese the esters were largely compounds of ethyl alcohol and caproic and butyric acids. The alcohol may have come from the lactose fermentation. It appears to be an important factor in flavor production. The agencies operative in the production of volatile acids and syntheses of esters are as yet undefined.

232. Milk-sugar.—The milk-sugar (lactose) is changed into lactic acid by the lactic acid-forming organisms, within the first few days after the cheese is made. This acid is combined with the other constituents as fast as it is formed. After a few days, the milk-sugar will have entirely disappeared from the cheese.[104] The relation between the milk-sugar and lactic acid is very close. It is necessary that milk-sugar be present in order later to have the lactic acid develop.

233. The salts.—Just what changes the salts[105] undergo or how they combine with the other compounds is not definitely known. It is supposed that the calcium salts first combine with the phosphates and later, as the lactic acid is formed, they combine with the lactic acid, forming a calcium lactate.

234. Gases.—In the process of cheese ripening, gases are formed, the commonest being carbon dioxide.[106] Exactly how this gas is formed is not known. It may be due to the formation of lactic acid from the milk-sugar or to the living organisms in the cheese.

235. Casein or proteins.—Complex ripening changes in the cheese take place in the casein compounds or proteins. Because of the complex chemical nature of the proteins and the various agents acting on them, it is difficult to follow these changes. This has led to different opinions regarding the ripening process. The various compounds thought to be formed from the casein or proteins are as follows:[107]

Paracasein (formed by the action of the rennet on the casein). Insoluble in brine and warm 5 per cent salt brine.

Protein. Soluble in warm 5 per cent salt brine.

Protein. Insoluble in warm salt brine or water.

Paranuclein. A protein soluble in water and precipitable by dilute hydrochloric acid.

Caseoses and proteoses. Protein derivations soluble in water and not coagulated by heat.

Peptones. Protein derivations simpler than the proteoses, soluble in water and not coagulated by heat.

Amido acids. Protein derivations soluble in water, least complex except ammonia.

Ammonia. The simplest protein derivations.

From the discussion of the constituents in the milk and cheese, it is evident that practically all the principal ripening changes are concerned with those taking place in the proteins.

236. Causes of ripening changes.—Authorities disagree as to the exact agents which cause the ripening changes. Some think they are due to the action of the enzymes in the rennet and those secreted in the milk. Others hold that these changes are due entirely to bacterial action. A combination of the two seems probable. The action of the rennet extract renders the casein insoluble and in the ripening process the proteins become soluble, the degree depending on the length of time the cheese is ripened. The amount of water-soluble proteins and protein derivatives is used as a measure of the extent of cheese ripening, considered from a chemical standpoint.

237. Action of the rennet extract.—Some authorities hold that rennet extract contains two enzymes, rennin and pepsin, while others think it is a single peptic ferment. These enzymes produce effects[108] closely related to, if not identical with, those of pepsin in the following particulars: neither the rennet enzyme nor pepsin causes much, if any, proteolytic change except in the presence of acid; the quantitative results of proteolysis furnished by the rennet enzyme and pepsin agree closely, when working on the same material under comparable conditions; the classes of soluble nitrogen compounds formed by the two enzymes are the same, both quantitatively and qualitatively; neither enzyme forms any considerable amount of amido compounds and neither produces any ammonia; the soluble nitrogen compounds formed by both enzymes are confined to the group of compounds known as paranuclein, caseoses and peptones.

Rennet exerts a digestive effect on the casein[109] which is intensified by the development of acid in the curd. The soluble nitrogenous products formed in Cheddar cheese by the rennet enzymes are the albumoses and the higher peptones. Experiments show that no flavor develops until the amido acids and ammonia are formed. When the rennet enzymes were the only digesting ferments in the cheese, there was no trace of cheese flavor. This is probably due to the fact that the rennet enzyme changed the casein into caseoses and peptones but did not form amido acids and ammonia. Some authorities[110] think that the enzyme galactase carries the ripening of the protein from this stage. The question arises whether these intermediate compounds must be found before other agents can form the amido acids and ammonia.

TABLE XV[111]

Showing the Effect of Different Amounts of ReneetExtracts on the Rate of Formation of SolubleNitrogen Compounds in Cheese Ripening

Quantity of Rennet Added per 100 Lb. of MilkPer Cent of Water Soluble Nitrogen Compounds in the Cheese
Initial32 days80 days270 days

2 oz
0.14
0.47
0.68
1.30
2 oz0.140.470.681.30
4 oz0.160.751.131.74
8 oz0.160.901.501.97
16 oz
0.14
1.26
1.70
2.04

The above table shows that the more rennet extract used the faster the cheese cures, measured by the amount of water-soluble nitrogen compounds formed in the cheese.

238. The action of the bacteria.—Authorities[112] disagree as to the groups of bacteria found in Cheddar cheese. This may be due to lack of proper classification. Some of the groups are: Bacterium lactis acidi, B. coli communis, B. lactis aerogenes, B. casei, Streptococci, B.[113] Bulgaricum and Micrococci. Authorities agree that the B. lactis acidi group is the most prominent. This group makes up 90 per cent or more of the total bacteria flora of the cheese in the early stages of ripening. In the course of a few weeks, however, this group is largely replaced by the B. casei group.[114]