placed in a 10 per cent. aqueous solution of cane sugar to which 4 per cent. of tartaric acid has been added, and this culture is set away at the room temperature. This cultivation is repeated four times after every twenty-four hours, or the culture is put away at 25° C. and recultivated twice at twenty-four hour intervals. A wort flask is inoculated from the last culture; then ordinary gypsum block cultures are prepared at 25° and 15° C. with the yeast thus produced, and these cultures investigated. In this manner quite small traces of wild yeast can be detected. In all cases a microscopical investigation is, of course, also carried out.

In the examination of cultures on gypsum blocks regard is paid to the appearance of the spores, the spores of culture yeasts generally containing a less refractive plasma with vacuoles, thus having an empty appearance, whilst the wild yeasts exhibit a strongly refractive plasma.

The above mentioned analysis of yeast by means of spore cultures on gypsum blocks can be simplified if the culture yeast in hand forms spores with extreme difficulty or not at all, as then the simple detection of the spores on the gypsum blocks at 25° C. is sufficient confirmation that the sample contains wild yeast or a foreign culture yeast.

Sporeless forms of the saccharomycetes can be prepared by the Hansen method, described in Section III.; the analysis is therefore simplified if a culture yeast of this kind is employed in practice. Since the asporogenous varieties of the saccharomycetes also form no films, this provides an additional means of detecting the presence of sporogenous, that is to say, foreign species; a wort culture being set aside to determine if film formation takes place. Analysis for Bacteria. In testing yeast for living bacteria an average sample is placed in yeast water and preserved at 25° to 30° C. When acetic acid bacteria are being sought, the beer can be kept at 32° to 33° C. if the

yeast sample to be examined is still in beer, or if that is not the case, a little of the yeast can be placed in beer and then subjected to this temperature. Should living acetic acid bacteria be present these are quickly developed by this process. If it is required to determine in a yeast sample the bacteria which are capable of developing in wort, thenof course wort is used instead of the liquids named above.

Testing the Contents of the Pure Culture Apparatus. -The above methods for the biological analysis of yeasts are applied in breweries to test the contents both of the pure culture apparatus and of the fermenting vessels.

In the first case a sample of the top beer is taken from the pure culture apparatus at the close of the primary fermentation by the side tube j (see Figs. 50 and 51). Wild yeasts are then detected by means of the tartaric acid method, and bacteria in the manner already described.

Testing the Contents of Fermenting Vessels. - So far as the testing of the fermentation vessels is concerned, this may be confined chiefly to a microscopical examination of the fermenting wort, especially when the yeast produced is not to be used as pitching yeast. The appearance of the yeast species used will in general be readily recognised by daily practice, so that a foreign admixture will be detectable by mere microscopical examination. A special . knowledge gained in this way is therefore of great advantage; but on the other hand it cannot be too strongly emphasised that a microscopical examination alone is not a perfectly reliable criterion, and this is especially the case when the culture yeast used is similar in appearance to a wild yeast (e.g., has more or less elongated cells). Foreign culture yeasts which may have found entrance in certain cases will, as a rule, not be recognisable; it is then even more necessary to apply physiological methods.

The sample is taken from the surface of the beer in a

sterile glass four to five days before the end of the primary fermentation. In the microscopical examination, the form of the cells is observed, and whether living bacteria, especially rod bacteria and Sarcina, are present. If it is wished. to test for wild yeast, the sample is set aside till a yeast deposit has formed; the latter is placed on gypsum blocks. and analysed according to the spore methods already described. The yeast is placed directly on the gypsum block because the wild yeast presumably present has just formed strong young cells at this juncture. At the same time a wort flask is inoculated with a little of the yeast, and the yeast generated here is employed next day in a new spore test. If wild yeast is found by this test, the yeast cannot be used for pitching. This holds also when Sarcina or other bacteria are present to an appreciable extent. Bacteria are always observed in the wort, but are usually dead. Wild yeast is likewise always found in practice in small amounts; when it cannot be detected by means of the ordinary spore method there is no reason for apprehension.

The table on page 139 is given as an example of the journal of a fermenting cellar.

Lindner's Drop Culture.-P. Lindner, in examining for wild yeast, uses the "drop" culture. This consists in taking out a certain amount of beer by means of a pipette and distributing the contents of the pipette, drop by drop, (generally 50 drops) on the bottom and the cover of a Petri dish. It is thus known what quantity there is in these 100 drops. The Petri dish is placed in a thermostat at 25° C., or left at the temperature of the room. A development is visible in the drops after the lapse of several days. If the number of germs is too large, the liquid is diluted with wort to a suitable extent, before the dropping is performed. If it is wished to determine the principal kinds that are present, the upper dish is used, in the drops.

of which the colonies are crowded at the lowest point, or are intimately mixed. All the drops are now touched with the finger, which has been cleaned and flamed previously, in order to obtain an average sample, which is then examined microscopically. To distinguish normal bottom yeast from wild yeast, the property is taken advantage of that the former aggregates in flakes, whilst the greater part of the wild yeast cells distribute themselves like dust in the drop. But since, as Lindner mentions, a part of the wild yeast also forms flocks, and the growths of culture yeasts on the other hand can assume a dusty appearance, other distinguishing features must be sought.

From Lindner's description of his method for analysing yeast in the brewery, it is seen that he draws his conclusions from the microscopical appearance of droplet cultures in hollow glass slips; this may be of use so long as it is remembered that cells of one and the same species, even when they are cultivated side by side in drops of liquid, often yield growths, the cells of which are so different as to seem to belong to several species. Under these circumstances culture yeasts may also develop cells with an appearance similar to one of the wild yeasts and vice versa. Each characteristic is, as is known, subject to variation, but this is especially so with regard to the form of the cells. This analysis, when combined with the ordinary microscopical one, is of advantage to the practised specialist, whose eye for the form and general appearance of the yeast cells has been specially trained.

9.-Hansen's Test of the Stability of Beer in Cask.

Samples from lager casks are taken by boring holes in the cask. The place is first cleaned with spirit, and a try-cock