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[Abstract. )



JOSEF PROKŠ, Ph. D., assistant at the Institute of Dairying, Polytechnic School,


From observations made on cheese made from skimmed and Pasteurized milk it has been demonstrated that the fermentation of milk has an influence upon the amount of water in white cheese. While the bacteria of the type Bact. lactis acidi give a normal percentage of water in white cheese. Bacterium coli fermentations generally produce a very watery curd, and butyric fermentations cause very dry white cheese.

EXPERIMENTS IN THE MANUFACTURE OF RENNET EXTRACT. RESWICK HUTSON LEITCH, M. A., B. Sc., professor of dairying, dairy research department, West of Scotland Agricultural College, Kilmarnock, Scotland.

Rennet extract as used in the dairy industry is obtained from the fourth stomach of the suckling calf; the stomachs of other ruminants are rarely used, and only then by small crofters in the preparation of homemade rennet.

Commercial rennet is now almost exclusively used in the making of hard-pressed cheeses, but makers of soft cheeses usually prefer to prepare their own extract, on which they place a high value.

The process of rennet making on a factory scale has not for obvious reasons been communicated to scientific journals, and little appears to be known of the methods of extraction and clarification which are of service on a large scale.

Experiments on the manufacture of rennet on an extended basis were carried out for three successive years by the dairy research department of the West of Scotland Agricultural College; during the seasons 1919 and 1920, over 3,000 gallons were successfully prepared according to our formula and issued to the dairy industry. In practice, the rennet gave excellent results. The following de scription summarizes the results of our work.

The stages of importance in rennet making are:
(1) The preparation of the raw material.
(2) The process of extraction.
(3) The method of clarification and preservation.

Rennet makers use the cured vells of commerce, which originate chiefly in Russia, Siberia, Bavaria, and Czechoslovakia. These dried vells are very convenient to handle, and keep well in cold storage, but they vary greatly in yield, and frequently contain bacteria of the most undesirable type. Thus we have found that B. subtilis, representatives of the B. coli group, and staphylococci occur almost invariably in the extracts of commercial vells, and there is no doubt that some common cheese faults can be traced to the bacterial flora of the rennet.

Good results in rennet making may be got by employing carefully handled material of home origin and treating it after the following manner: As soon as possible after the slaughter of the calves

at the abattoir, the fourth stomachs are severed from the rest of the intestines and conveyed to the factory in waterproof bags. The mesenteric membranes and the adhering fatty tissue are now removed with a trimming knife, the curdled milk and liquid contents of the stomach expressed with the finger and thumb, and the stomach inflated. Some manufacturers make an extract of the partially digested stomach contents and recover therefrom the enzyme secreted in the hours before slaughter.

The distended membranes are rapidly air-dried at a temperature between 20° and 25° C. for 10 days, and then kilned at 30° to 35° C. for a further period. Stomachs cured in this way are tough and pliable but not brittle. Effective drying of the vells greatly diminishes the amount of mucus which emerges during the subsequent extraction, and thus renders filtration easier. The fresh vells may be salted before being distended. Such vells keep well and are not attacked by rats or mice as are unsalted vells, but they absorb moisture in a damp atmosphere to the detriment of the extract.

The dried vells are cut up with a mincing or slicing machine and added to the extracting fluid at the rate of 8 to 10 vells per gallon of water.

The composition of the extracting fluid is of first importance. A simple extraction with brine gives good results, from 5 to 10 per cent of salt being employed. A combined salt and calcium chloride extraction (5 per cent each) is also very effective, especially with vells which have been cured for a short period only. It is important that the extracting fluid be maintained near the neutral point. Acid extractions are turbid, difficult to filter, and do not keep well. To maintain this proximate neutrality, either precipitated chalk or bicarbonate of soda in regulated amount may be used. The pH value of the extracting fluid should lie between 6.0 and 6.4. If commercial vells are employed, a preservative is necessary to restrict the fermentation due to microbial action, and for this purpose boric acid is universally used at the rate of 2 to 3 per cent. Thymol crystals are occasionally employed. Boric acid activates as well as preserves the rennet extract. In our work, and especially with homecured vells we have found that it is better to withhold the boric acid until the extraction process is complete.

When the extract is sufficiently strong, the extracting fluid is decanted. At this stage it may be partially clarified by centrifugalization or by filtering through calico, more especially if the extract be thick and slimy.

The fluid is now additioned with glycerin, and from 5 to 10 per cent salt (or until the salinity of the extract is approximately 14 Beaumé), but the glycerin may be omitted if the rennet at this stage is fairly clear and is to be marketed soon. Boric acid, if not previously added, is mixed with the glycerin and added along with the salt. The addition of salt at this juncture causes a slow precipitation.

The extract thus treated is allowed to sediment, preferably out of contact with air. In a few weeks, the clear rennet may be siphoned off and stored in jars or in barrels. (Some manufacturers sediment rennet extracts in bulk for two or three months.) If the rennet shows no signs of incipient clearing after two or three weeks, it

must be filtered. Clarifying agents like zinc dust, kieselguhr, powdered chalk, kaolin, and talc added to a turbid rennet are of little service in clearing the solution. Most of them absorb a good deal of the enzyme without having any effect on the clarity.

The majority of filters possess a strong adsorbing power for rennet. If the turbidity is removed by a filter press of the ordinary type, much of the enzyme is retained by the filter, and the resulting rennet is weak. On a small scale, Chardin paper and gravity filtration will give good results. It may be observed that a clear rennet is not obtained until the pores of the filter become partially blocked up, or until a semipermeable membrane forms over its surface. Charcoal filters possess the greatest adsorbing powers for the enzyme, and have no utility in rennet manufacture. We have found that a sectioned filter, in which close and loose layers follow one another, gives a clear extract, and if constructed of proper filtering materials, removes comparatively little enzyme. Filtration through salt or kainit will clear very turbid solutions, but a very considerable amount of the ferment is lost. Filtration through suitable grades of silver sand gives excellent results.

The turbidity of fresh rennet extracts, which is caused by the presence of mucus of a nucleo-protein nature, may also be removed by common protein precipitants or coagulants. Unfortunately, with the possible exception of salt, few of these are of any service, because heavy precipitation, while it removes the mucus, at the same time removes much of the enzyme. Lactic acid at the rate of 0.05 per cent, sweet cheese whey of an acidity not more than 0.02 per cent, and 2 per cent boiled milk are among the most useful precipitants. These agents if judiciously employed cause a relatively small loss of enzyme. They usually take from 14 to 21 days to clear the solution.

The exact form in which the rennet enzyme occurs in the extract is difficult to determine, but it is clear from examination that it is in colloidal and not in simple solution. If it were possible to isolate the pure enzyme, and then add it to distilled water, one would find that such a solution would quickly deteriorate. The enzyme must have some suitable agent with which to associate, and this must be a colloid or of a gelatinous nature.

Most rennet extracts are colored with a salt-saturated caramel solution, but neutral annatto and bismark brown may also be used. These agents are said to exercise a protective action by excluding certain harmful light rays, but it is doubtful if they have any utility in commercially prepared extracts. In any case, rennet is mostly stored in barrels or in stone jars, and is seldom exposed to light long enough for the light to exercise any destructive effect.

Rennet in bulk or in jars should be kept at a low temperature. At temperatures above 606 F. the loss of strength is accelerated. As far as possible oxidation should be guarded against; exposure to air undoubtedly increases the loss during keeping. If a large surface of a bulk sample is necessarily exposed during prolonged sedimentation, a layer of liquid paraffin on the top will prove helpful.

The degradation of rennet extracts during storage is caused by several factors, among which oxidation effects and the action of microorganisms are the chief. These microorganisms, which include members of the coliform and the anthracoid group and more than one species of yeast, are also inimical to quality in cheese.




MASAYOSHI SATO, D. Sc., Hokkaido Imperial University, Sapporo, Japan.

The Mongolian cheese, or Naii Tofu, is made in a primitive method during the summer season when the milk is abundantly secreted. First of all, the milk is coagulated by the natural lactic fermentation, and after the whey is separated the coagulated casein is taken out to be boiled and stirred up in a kettle until its serum evaporates and its viscosity increases. It is then put in a wooden box and cooled for a short time to be again coagulated; and, when it is taken out and dried in the sun, it is ready to be preserved in a receptacle.

The soft-dried Naii Tofu is good to eat, but the hard-dried form is to be boiled or roasted. It is said that the Naii Tofu is a necessary companion of Mongolians when they go out hunting or traveling.

The sample used in the writer's experiment was of an oblong shape, 16 to 19 centimeters in length, 9 to 9.5 centimeters in width, and 1.52 centimeters in thickness, weighing 0.274 to 0.38 kilo. It was very hard and yellowish. The analysis made showed that it contained 12.630 per cent of water, 22.400 per cent of fat, 62.228 per cent of protein, etc., and 3.290 per cent of total ash. As to the soluble nitrogenous compounds, it showed when water-free 1.98 per cent of soluble nitrogen, 0.259 per cent of ammoniacal nitrogen, 0.481 per cent of soluble protein nitrogen, and 1.244 per cent of amide nitrogen.

The above is the result of the analysis made on one sample only. To get a precise result on each compound, more experiments on various samples are required.


Honorary chairman, MAGNUS CHRISTIANSEN, professor, Royal Technical Agri

cultural College, Copenhagen, Denmark. Chairman, K. L. Hatch, assistant director, agricultural extension, University

of Wisconsin. Secretary, E. V. ELLINGTON, head of department of dairy husbandry, State College of Washington.

Y. W. C. A. ASSEMBLY HALL, Syracuse, N. Y., Friday, October 5, 1923-1.30 p. m. Chairman HATCH. The eighth session of the World's Dairy Congress will now come to order.

I want to present Professor Christiansen, professor at the Royal Technical Agricultural College, Copenhagen, Denmark, who will act as our honorary chairman. [Applause.]

Of course most of you gentlemen from the States are acquainted with our secretary, Mr. Ellington.

With these distinguished gentlemen on my right and left for support, we are certain that your chairman this afternoon will be able to at least read the program,

The directions for the conduct of the program (which was delayed by the late arrival of the trains and adjourned to this hour this afternoon) are to proceed in the order in which the numbers appear on the program. When the author of any paper does not appear in person, the paper will go to the end of the list. We will proceed in the order as announced.

Inasmuch as Professor Borland is the first speaker present to read his paper, I now have the pleasure of introducing to you Professor Borland, head of the department of dairy husbandry, Pennsylvania State College. Professor Borland.


ANDREW ALLEN BORLAND, head of department of dairy husbandry, Pennsylvania

State College, State College, Pa. Agricultural extension work consists in the instruction of those who are not resident students at an educational institution. It presents to such persons the teachings of the colleges of agriculture and the findings of the experiment stations by means of field demonstration, publications, and otherwise.

Prior to 1914 agricultural extension work was carried on in a general way by means of farmer's institutes, correspondence courses, lectures, and farm visits by members of the instructional and experimental staffs of the agricultural colleges and by a few county agricultural agents. The Smith-Lever Act, passed by Congress May 8, 1914, provided a definite basis for a permanent national system of agricultural extension work, including practical instruction and demonstrations in agriculture and home economics, to be carried on 77612-24



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