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The samples were taken from cheese of very inferior quality and also from the better grades, with the thought that the results might give some indications as to the groups of organisms to be avoided, as well as the desirable type. The samples, 40 in all, from 25 or more factories, as purchased from the local stores, were plated by the usual methods and also sectioned with the microtome. The predominating groups were studied culturally and microscopically. In all, 265 cultures were isolated from the 40 samples. The cheeses were, previous to examination, classified into three general groups from the standpoint of flavor, texture, and general quality. The cultures isolated were taken from the plates in such a manner as to indicate the relative abundance of any particular type in any sample.
The cultures were subjected to the usual laboratory tests and classified into the following groups: (a) Spore formers; (b) gram-negative rods; (c) lactobacilli; (d) Streptococcus lactis (Lister) Löhnis; (e) cocci; (f) streptococci other than S. lactis, and (9) yeasts.
The spore formers have been mentioned in the previous literature by Duclaux as being a factor in the ripening of cheese; and in the present work the group was found to predominate in the more undesirable grades. Of the 265 cultures isolated, 54 were spore formers, and from the standpoint of numbers they were the largest group isolated. As stated above, other workers used only highgrade cheese in floral work, and did not at the completion of the work draw conclusions as to the undesirable types, but rather as to the types that normally existed in the high grades of cheese. Of the cultures from the better or "above average” grade of cheese, only 9 per cent were spore formers, a small percentage in relation to other groups. As the quality of the cheese became of a lower type the number of spore formers increased. Although the rods which produce spores usually attack casein and render it soluble, the products resulting apparently have an undesirable effect upon flavor.
Of the coccus types studied (27 strains in all) 20 were white, and 6 yellow, while only 1 produced an orange pigment. The cheese of all grades contained approximately the same proportionate number of cocci, and no correlation was found to exist between the quality of the cheese and the number of cocci present. This group. however, may play a large part in the ripening changes, as microscopic preparations made from cheese which has partially ripened show large colonies of cocci in dense masses throughout the cheese, indicating that the coccus types have grown, reproduced, and attacked the surrounding medium for their food supply.
Of the 265 cultures isolated, only 26 were streptococci (other than S. lactis). The greater number of these were derived from the poorer grades, and only one culture from the better grade of cheese. Probably this group is the least abundant of all types in cheese, and if it plays an important part in the ripening it no doubt attacks the casein in conjunction with some other group. This fact was indicated in the floral work of Miss Evans, at Washington, who found that certain types of streptococci when used as a starter with other types affected the development of flavor appreciably.
The group of gram-negative rods included such types as attack lactose and nearly all liquefy gelatin. This group includes organisms of the colon and proteus types. In abundance they are second only
to this group:
to the spore-forming group as 52 of the 265 cultures belonged in this class. Î'he action of this group on the ripening is generally regarded as detrimental, and their presence accounts for gas and undesirable flavors in the poorer quality of cheese.
The lactobacilli (Bacterium casei, B. bulgaricus, etc.) are one of the most important groups involved in the ripening changes of Cheddar cheese. Other types of cheese, as Emmental, Edam, Parmesan, etc., contain large numbers of these organisms and no doubt in all of these cases the lactobacilli play a part in their curing. This group is characterized by gram-positive rods of various lengths, usually long. Nearly all types stain deeply with methylene blue, while a few stain with distinct granules. The group is present in milk in small numbers and develops rapidly in the cheese after the first few days in the curing room, gradually replacing other types. Four distinct strains are recognized by Freudenreich, divided on their staining reactions, action upon milk, and morphology. In all cases where this group has been studied in relation to cheese ripening, it has been found that they are largely responsible for the development of the flavor, and also play a part in the breaking down of the casein. In the above work it was noted that the cheese classed as above average contained the largest number of lactobacilli, while the inferior grades contained fewer numbers. Of the cheese “ above average " 30 per cent of the cultures were lactobacilli, while 21 per cent of the "average” and 14 per cent of the cheese “ below average " belonged
More has been written on s. lactis and its relation to Cheddarcheese ripening than on any other of the common cheese organisms. Russell, at Wisconsin, in 1904, pointed out that this organism is present in large numbers in the early stages of the ripening, and he concluded that it plays a principal role in the ripening. More recent work has shown that the part played by organisms of the S. lactis type is primarily that of changing the sugars into lactic acid. The acid furnishes a medium for the development of other and more important groups. The predominance of organisms of this type during the first few days of curing is due largely to the addition of S. lactis starters in the milk previous to cheese making. In the present work, only 29 cultures were isolated. This does not give a fair representation of the conditions which actually exist, as the age of these samples was such that these organisms had largely disappeared.
Such a few cultures of yeast were found, three in number, that the group has not been considered in this paper in their relation to cheese quality. Of the three strains, two were isolated from the better class of cheese. Since the completion of the above survey, however, a cheese of poor quality, purchased on the open market, has been examined and found to contain a predominating yeast flora.
The floral changes in a typical American Cheddar cheese can be summarized by saying that in the early stages the organisms of the $. lactis type develop rapidly. In the better-quality cheese, the lactobacilli, cocci, and streptococci develop in the later stages until the fourth or fifth month, when the number of organisms diminishes. In the poorer grades of cheese the sporeformers and gram-negative rods develop after the initial predominance of S. lactis.
PASTEURIZATION OF MILK FOR CHEDDAR CHEESE MAKING IN
Chas. STEVENSON, dairy instructor, Department of Agriculture, New Plymouth,
The question of the quality of milk intended for cheese making is one which has for many years exercised the minds of those engaged in the industry in New Zealand. It is well known that the condition in which the milk is delivered to the factories is the chief factor governing the quality of the cheese produced. If all the milk delivered was up to the standard of the best quality, no difficulty would be experienced in producing a uniformly good quality of cheese. Unfortunately, in almost every district we find some dairy farmers who do not study the production of milk from a sanitary point of view, with the result that milk of such varying qualities is delivered that the production of a uniform quality of cheese from day to day is found to be almost impossible.
In view of the success achieved in the Pasteurization of cream for butter making, the attention of cheese makers was directed to the possibility of adopting the same system with regard to milk required for cheese making as a means of overcoming these difficulties. Many experiments were carried out in the Pasteurization of milk used for cheese making, but only limited quantities were treated. Sufficient data were obtained, however, to indicate that the quality of the cheese was improved to such an extent as to warrant further steps being taken. For some time it was found impossible to make much progress along this line, owing to the fact that machinery capable of heating large quantities of milk in a limited time was not available, but with the introduction of regenerative heaters this difficulty was eventually overcome.
These machines, which are of Danish manufacture, were first imported into this country in the year 1914, and are made in different sizes, with a capacity varying from 800 to 1,800 gallons of milk per hour, while heating to a temperature of 1606 to 165° F. When working these heaters at full capacity, a transference of heat ranging from 40° to 45° F. is made from the hot to the cold milk. Most of the machines in use here are of the larger type, and all are fitted with a steam inlet sufficiently large to utilize exhaust steam where available. A complete plant, which consists of a milk-receiving vat, a regenerator, two milk pumps, and a large cooler, will occupy a floor space of 20 feet long by 12 to 14 feet wide, and can be installed to-day at a cost of £365. All necessary piping is made of the best
a drawn brass, tinned and fitted in short lengths, and jointed with brass unions. The coolers found most suitable for this work are those of the horizontal tubular type, 12 feet long by 4 feet high, fitted with two water inlets and a like number of discharges.
The supply of water for cooling purposes presents practically no difficulty, as the milk leaves the regenerator at a temperature of 115° to 120° F., and requires only to be further cooled to 86° or 90° F. Many dairy companies have adopted the practice of pumping the waste water from the cooler to storage tanks and using this water again for ordinary factory purposes. By this method Pasteurization places no extra claim on the water supply.
Observations made over a number of years indicate that where live steam only is used for Pasteurization, the increase in fuel consumption is from 10 to 15 per cent, but where exhaust steam is also used practically no increase is shown. In order to carry on this work successfully, and as economically as possible, a plentiful supply of dry steam is necessary. Where the larger Pasteurizing plants are installed a steam boiler of at least 20 horsepower is required.
The manufacture of cheese from Pasteurized milk presents no difficulty whatever to the experienced cheese maker; in fact, in handling this class of milk, which after careful Pasteurization is in practically the same uniform condition from day to day, the work is considerably simplified. Perhaps the most important point to be observed is the maintenance of an even temperature. Practically all the most serious defects found in this class of cheese have been traced to lack of care during the heating process. A temperature of from 160° to 165° F. is generally aimed at, and with reasonable care no difficulty is experienced in maintaining a temperature within these limits. If the temperature of the milk be permitted to fall below 160° F. the flavor of the cheese is deteriorated, and, on the other hand, if it rises much above 165° F. the body and texture are invariably injured, the result being a mealy bodied cheese.
A good-quality starter is essential, and this, applied at the rate of 1 to 17 per cent, has been found to give excellent results. During the earlier stages of this work in New Zealand a quantity of hydrochloric acid was added to the milk after Pasteurization, but close observation indicated that this practice was of no assistance, and consequently it has now been abandoned. In dealing with Pasteurized, as against un-Pasteurized, milk for cheese making, it has been found necessary to increase the amount of rennet used. An increase of approximately 1 ounce per 1,000 pounds of milk is sufficient to produce a good coagulation.
Among the many advantages claimed for this method of cheese manufacture, perhaps the general improvement in quality is the most important. Numerous instances could be given where the average grade of cheese coming forward from different factories has risen to the extent of two or three points after the installation of a Pasteurizing plant, and at all factories where the work is carefully carried out second-grade cheese has been entirely eliminated. During the years 1915 to 1917, owing to the inadequacy of shipping facilities, it became necessary to store cheese here for lengthy periods; and at that time the superior keeping qualities of the cheese made from Pasteurized milk were most outstanding.
At different stages during the process of cheese manufacture losses of fat are observed, but these losses are considerably decreased when the mik is Pasteurized. One of the chief difficulties of this kind, the working of slightly overripe milk, is completely overcome by the Pasteurization method of manufacture. Careful observation has shown that the loss of fat in the whey is, on an average, 0.05 less with Pasteurized than with un-Pasteurized milk. This reduction or elimination of the losses, together with the general improvement in the quality of the cheese, proves clearly that from an economic point of view, the question of installing Pasteurizing plants in cheese factories is one which is well worthy of the earnest consideration of those engaged in the industry.
Although it has not yet been considered expedient to introduce legislation making compulsory the Pasteurization of milk for cheese making, every opportunity has been taken by officers of the dairy division of New Zealand to place before the dairy companies concerned the advantages of the system, and the progress made is indicated by the large number of plants which have been installed since the inception of this system.
Prior to the year 1914 the manufacture of Cheddar cheese from Pasteurized milk was practically unknown in New Zealand, while to-day a total of 38,000 tons of cheese, approximately two-thirds of the output of the whole Dominion, is inade by this system. During the past three years developments have been somewhat retarded owing to the great increase--practically 100 per cent—which has taken place in the cost of the necessary machinery. Prices are now returning to normal, however, and further progress in this connection is therefore assured.
The experience gained during the past seven years proves conclusively that the adoption of the system of Pasteurization as applied to milk used for Cheddar-cheese making in New Zealand has been an unqualified success, and it is confidently anticipated that in a short time the system will be in operation in all the cheese factories in the Dominion.
RELATION OF LACTIC BACTERIA TO CHEESE RIPENING.
('ONSTANTINO GORINI, Ph. D., director of the bacteriological laboratory of the
Agricultural High School, Milan, Italy.
In response to the invitation of the committee on research and education of the World's Dairy Congress, I take pleasure in reviewing briefly the contribution which I have made to the question of lactic ferments in connection with cheese ripening.
My scientific researches and practical experiments have shown that two types of lactic ferments are concerned in cheese ripening; first, the ferments pointed out by Freudenreich, which do not attack casein in an acid reaction (simple lactic ferments); second, the ferments indicated by me, which attack casein even in an acid medium (acidoproteolytic ferments).
I was led to the discovery of this second type of ferments after I demonstrated in the year 1892 that the Bacillus prodigiosus clots milk by a double means, by acidity and by rennin, later dissolving the curd with an acid reaction. This was the first example of an acidoproteolytic bacterium. In 1894 I showed that three other species of bacteria acted in the same manner: Bacillus indicus, Proteus mirabilis, and the Ascobacillus citreus, a true milk bacterium. At that time I proposed to add to the lactic ferments already known a new type, acidoproteolytic ferments, advancing the hypothesis that they contribute to the ripening of cheese.
In 1897 I further demonstrated that the saccharolytic and proteolytic activities of bacteria living in milk are dependent upon environ