A method based on the same principle, although executed in a different manner, has been used in Switzerland during the last few years.

The advantages of this curd test over the earlier fermentation tests are as follows:

1. That the curd prepared from individual samples of milk more closely conforms to cheese conditions, thereby permitting a more accurate determination of the value of milk for cheese.

2. The development of gas and the relative amount of the same can be more easily traced in the curd than in the milk.

3. The removal of the milk serum with its abundance of fermentable sugar renders a more accurate test possible.

4.

The detection of odors in milk that has been tainted by direct absorption is rendered possible.

Showing different stages of test. A, milk; B, broken curd in whey; C, matted curd.

A study of different milks by this test shows that almost all samples contain slight evidences of gas, if kept under conditions unfavorable for the keeping of milk, as is the case in the test.

During the heated season, the conditions are more favorable for the rapid development of these bacteria, and therefore, "gassy" fermentations are more troublesome in the summer months. A study of different herd milks for a considerable period of time shows, as might be expected, that this condition is not abso

lutely constant, but nevertheless, the presence of bad taints in certain milks has been found to be surprisingly uniform. In some herds the milk is so carelessly received and handled that gas-forming bacteria are almost a constant accompaniment; in others, the undesirable condition is transitory, some days gas appearing in quantities, to be followed by a period of comparative freedom from taints. In such cases the difficulty is temporary, the climatic conditions often being the deciding factor. In still other cases the herd milks are always free from any suspicion of taint. These represent in general the patrons that exercise the greatest care in their treatment of the milk. In case the curds are kept for 24-36 hours some gas will appear in even the very best milk, as gas-producing organisms are present to some extent under the most favorable circumstances. In general, however, a tainted or defective condition, as revealed by the curd test, is usually traceable to the introduction of foreign matter such as filth, dirt or dust.

It not infrequently happens that a tainted condition may appear in the curd that is not associated with the production of gas. In some cases this arises from direct absorption of undesirable odors, either from the animal herself or from exposure after milking. It is a current belief that milk will not absorb odors when it is warmer than the surrounding air, but such an hypothesis has been experimentally determined by one of us (R.*) to be erroneous.

Leaving the warm milk in the stable, even for a limited time, where obnoxious odors are almost always present, is detrimental, as it gives an opportunity for the direct absorption of taints. Taints of this sort are not very prominent in the curd test, yet they can frequently be detected, as they are retained in the milk and are more readily perceived when the milk is

warm.

It frequently happens that digesting bacteria that dissolve the casein without the production of gas may also be present. In such cases, the casein passes partially into solution. and is lost in the whey. The taints caused by this class of organisms are peculiarly offensive. Milks that contain such bacteria in any considerable numbers give a materially diminished *Unpublished data.

yield of cheese, and illustrate the unfairness of the guarantee principle that demands that a maker should make a pound of cheese from a certain quantity of milk regardless of conditions.

IMPROVISED CURD TEST.

The apparatus for the Wisconsin Curd Test resembles in some respects the Gerber apparatus. A homemade test can be improvised that will give good results, but we would advise the use of one of the perfected tests as it is more convenient.

The apparatus for the test consists of a wash tub (see Fig. 2) that is half filled with warm water, a set of pint fruit jars (C) for the different samples, a pipette (p) for measuring the rennet, and a case knife (k) for breaking the curd.

HOW TO MAKE A TEST.

To make a test, fill a jar half full of milk. Set samples in the tub and fill the same half full of warm water. Usually water at 115° F. will raise the temperature of the milk to the desired point, viz., 98°. If the milk is very cold care should be taken not to use too hot water to prevent cracking the jars.

When the temperature of the milk reaches 98° F., add to each sample by means of a pipette, ten drops of rennet extract and mix thoroughly. Allow the jars to remain undisturbed until milk is curdled, then break the curd into small particles by stirring with a case knife, in order to better expel the whey. In using thermometers for taking temperatures, or knife for cutting the curds, care should be taken to rinse. after using in each sample so as to prevent the transference of many organisms from one sample to another.

The whey should be poured off as soon as the curd settles to the bottom, this process being repeated at frequent intervals until the curd mats into a solid This expels the excess of whey which contains the fermentable sugar, thereby simulating cheese conditions more closely. The temperature of the surrounding water should be maintained from six to

mass.

eight hours to favor a rapid development of the contained organisms.

This improvised apparatus will enable any cheese maker to use the test with satisfactory results, but time can be saved and greater convenience secured if apparatus is devised for the particular purpose in hand. When the curd test is in constant use some special apparatus will be well worth the expense.

INTERPRETATION OF RESULTS.

If the milk contains no deleterious bacteria the curd when cut will present a firm, even texture as shown in Fig. 7. If gas-producing bacteria are present the texture of the curd will be more spongy, the cut surface showing a number of holes varying in size, depending upon the prevalence and gas-producing ability of the undesirable bacteria as shown in Figs. 8 and 9.

Care should be taken to discriminate between purely mechanical holes that are formed by the failure of the curd to mat closely and those caused by the fermentation of gas. Mechanical holes are irregular in form and more variable in size, while holes formed by gas are circular in outline and more uniformly distributed throughout the whole mass of curd. As gas continues to be formed, the curd puffs up and some of the gas may escape into these mechanical openings, distending them, and giving them the appearance of regularly formed gas holes. The size of the gas holes in the curd is largely dependent upon the duration and activity of the fermentations. The longer the curd is allowed to ferment at a proper temperature, the larger and more numerous will be the holes. Even in a good milk, a few holes will develop if the curd is held for 24 hours or more, but the presence of a few "pin holes" within six hours need not condemn a milk unless accompanied by undesirable odors.

The conditions under which the curd test is conducted accelerate the fermentative action, so that a milk that might show no symptoms of gas formation until the cheese was on the shelf, would be detected when subjected to the curd test. Milks that are sufficiently contaminated to produce floating curds will show a very spongy texture in the test in a few hours.

No hard and fast rules can be given for the interpretation of the results of the curd test, but an ordinary operator will very quickly learn to discriminate between milks that should and should not be accepted.

It should be borne in mind that the formation of gas is generally accompanied with the production of other decomposition products that possess more or less pronounced undesirable flavors and odors and that the injury to the cheese is due to this more than to the mere mechanical presence of gas.

It is also possible that taints may be produced by bacterial decomposition in cases where no gas is formed. This is particularly true with that class of organisms that act upon the albumen and casein instead of the milk sugar. Those bacteria that find their way into the milk through the introduction of filth and dust are particularly prone to produce this change, and this type of fermentation is very often found during the summer months. In the curd test such milks are not condemned upon the texture of the curd but upon the odor which is more or less pronounced when the bottles are opened.

CONCLUSION.

From the foregoing it is evident that the Wisconsin curd test in the hands of the factory operator is a valuable adjunct in enabling him to determine the presence of taints which might otherwise escape detection. The losses that accrue from these sources are in the aggregate very large and the difficulty hitherto has been that the cause of these troubles could not be located with sufficient accuracy to enable restrictive measures to be employed. The Wisconsin curd test fills this want and has been shown to be an efficient detective of tainted milks. It is therefore earnestly recommended that this test be employed in factories when difficulties of this sort are met with.

While the curd test is especially useful in helping to solve the controversies that arise in every factory between maker and patrons as to the presence and origin of tainted milks, the other factory tests mentioned in this bulletin should not by any means be ignored as they will often throw light upon the character of the milk.