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It is a bottom yeast form which does not secrete invertase and in consequence cannot ferment cane sugar; it is also incapable of fermenting maltose. It therefore does not form more than 1 vol. per cent. of alcohol in wort; on the other hand it forms 4:3 vol. per cent. of alcohol in yeast water containing 10 per cent. of dextrose.
Sacch. apiculatus, like many other fungi, undergoes a remarkable variation. Thus Hansen found that of two growths investigated by him, one gave 3 and the other 4:3 vol. per cent. of alcohol. Amthor investigated two varieties, of which one furnished 3.25 and the other 4:56 vol. per cent. of alcohol, and Müller-Thurgau found that in seven cultivations in sterilised grape juice the alcohol production varied between 2-5 and 3.8 per cent. by weight. Will had two growths, one of which evolved a mouldy smell, the other an amyl ester-like bouquet. But whether such variations are permanent or not, or on what they depend, has not been investigated.
Its extraordinary power of multiplication is characteristic of Sacch. apiculatus. This and its competitive relations with Sacch. cerevisie have been mentioned on p. 230.
Hansen's investigations on the circulation of Sacch. apiculatus in nature are described on p. 246. This fungus is generally distributed in nature on fruits and also in soil. Müller-Thurgau found it in the latter to a depth of 20 to 30 cm., and Berlese to a depth of 36 cm.
According to Will it is found commonly in bottom fermentation breweries, but only in small amount. It is generally present in those Belgian breweries where beer is prepared by spontaneous fermentation.
According to the investigations of Müller-Thurgau and Wortmann it is especially detrimental in the manufacture of wine, as it has a retarding influence on the fermentation, but not, however, if the liquid contains 3 vol. per cent. of alcohol. It is most effective during the first stages of fermentation. Sacch. apiculatus possesses in a higher degree than true wine
yeasts the power of decomposing and absorbing organic acids. MüllerThurgau's experiments show that this property also asserts itself when it works simultaneously with true wine yeasts, as is the case in the progress of ordinary wine fermentations. Finally, by the formation of volatile acids and other products it is injurious to the bouquet and flavour of the wine. According to investigations by W. Seifert it formed the largest amount of volatile acid (0.064 per cent.) and volatile ester of six pure yeasts in the same grape must. The amount of ester expressed in cubic centimetres of to normal alkali on 100 c.c. of wine corresponded to 10-8, while with the other yeast species it varied between 1.32 and 4:4. When it ferments grape must a cider-like taste and smell are exhibited. Although the increase of Sacch. apiculatus occurring on fruit and grapes is not prevented by the addition of pure yeasts to the must, yet, as experimental results show, its detrimental influence can be very considerably restrained by the addition of a quick-growing, vigorously-fermenting yeast (Müller-Thurgau). According to some French investigators Sacch. apiculatus yields a good cider with a strong bouquet; but, according to Müller-Thurgau, it has, on the contrary, a harmful influence on the cider fermentation.
Mycoderma Species. These fungi are the so-called true film fungi which are distinguished by the rapid formation on nutrient liquids, particularly on beer and wine, of a covering film having air between the cells. The cells are usually short and sausage-shaped. They are strongly aërobic.
Mycoderma cerevisiæ, Desm. (Sacch. mycoderma). — Several species are included under this name. The species usually to be found in the Copenhagen breweries forms a dull, gray, wrinkled film on wort and beer. The cells contain from 1 to 3 refractive granules, which are of a fatty nature. This fungus does not induce fermentation, contains no invertase, and occurs in practically all lager beer, but does not succeed in growing so long as the bottles are well stoppered.
It is known with certainty that at least some of these forms do no harm in breweries under ordinary conditions ; this holds good with regard to the species observed by Hansen, A. Petersen, Grönlund, Jörgensen and Prior. Bělohoubek and Kukla, on the contrary, mention a species which causes turbidity in beer. The same applies also to three forms observed by Lasché in America, which are said to cause a bad smell and taste in beer. They are said, moreover, to produce alcohol in wort. Lafar has described an allied species which forms acetic acid in beer.
These forms are easily obtained if beer or wine is allowed to remain at a temperature of 10° C. with a free supply of air.
Mycoderma vini, Desm. (Fig. 120), is very nearly related to, or is probably identical with, the above species ; it forms the film of wines. This film can become over 1 cm. thick. The fungus acts, like the other species, as an oxidising agent on the alcohol in the wine, forming carbonic acid
Fig. 120.--Mycoderma rini, Desm. About $. (After Wortmann.)
and water. It can also attack other constituents of the wine. By decomposing a part of the free acid it favours the growth of acetic acid bacteria, and consequently the production of a vinegar taint. Wortmann states that this fungus can also influence directly the flavour of a wine.
Forti mentions a Mycoderma species which has a detrimental influence on yeast in wine.
W. Seifert has made complete experiments with two related forms isolated from red wine, which he names Mycoderma vini I. and II.
The cells of Mycoderma vini l. are 3 to 10 m long, and 2 to 4 u broad. The films are smooth at first, later strongly wrinkled, coherent and grayish-white. The temperature limits for growth in wine with 8 vol. per cent. of added alcohol are : Maximum, 30° C.; optimum, 25° to 28° C.;
and minimum, 5° to 6° C. This species grows even in the presence of 12:2 vol. per cent. of alcohol, and vigorously attacks malic acid. In an artificial culture liquid (Pasteur's solution) containing malic acid and 48 vol. per cent. of alcohol, it formed 0-152 per cent. of glycerine in fourteen weeks ; at the same time the whole of the alcohol had disappeared. In ordinary Austrian white wine it increased the amount of glycerine (0-68 per cent. to 0.82 per cent.), formed acetic acid (0-904 per cent.), and reduced the amount of alcohol (7.8 to 38 vol. per cent.) in twenty-six days.
Mycoderma vini ll. differs from the above species in having temperature limits for its growth in wine with 8 per cent. of alcohol as follows: Maximum, 28° to 30° C.; optimum, 22° C.; and minimum, 1° to 2° C. This fungus attacks malic acid only to a small extent. In the culture solution referred to above, it only formed 0·016 per cent. of glycerine after fourteen weeks, and at the same time the amount of alcohol was only lowered from 4.8 to 4:1 vol. per cent.
No increase of glycerine was effected in white wine after twenty-six
Fig. 121.- Monilia candida (Bonorden), Hansen. Sedimentary yeast. Vacuoles
with refractive granules occur in some of the cells, 1999. (After Hansen.)
days, only 0.064 per cent. of acetic acid was formed, and the alcohol was only reduced from 7.8 to 6-8 vol. per cent.
Tartaric acid is practically not attacked by either species, and citric acid not at all. The glycerine and acetic acid formed are gradually used up again.
Monilia candida (Bonorden), Hansen. This fungus (Figs. 121, 122 and 123) is generally found in nature on fresh cow dung and on fruit. The following investigations described are due to Hansen :
In nutrient liquids containing sugar this fungus quickly develops a growth of Saccharomyces-like cells, in which vacuoles with one or two strongly refractive granules frequently occur (Fig. 121). When such a culture is allowed
to remain some time the cells become elongated, and there results finally a complete mycelium, a mealy, white, tufted growth of mould which forms chains of yeast-cell conidia or divides into members like Oidium (Fig. 123, d). This growth also appears on solid culture media.
When young and vigorous cells of this species are seeded in a fermentable nutrient solution, e.g., beer wort, a rapid and vigorous fermentation like a top fermentation is effected ; even while the bubbles are rising a film forms on their surface. When the frothing has finished, the film gradually extends over the whole surface; during this pro
FIG. 122. - Monilia candida (Bonorden), Hansen. Cells derived from a young
film growth. (The shining granules appearing in Fig. 121 are not shown here.) 1904. (After Hansen.)
cess the large film-covered air bubbles gradually burst, and often cause folding of the film. If old cells are seeded the film forms before there is any perceptible macroscopic sign of fermentation. In wort after sixteen days this species formed 1:1 vol. per cent. of alcohol; after nine and a half months, 6.5 vol. per cent. ; and after twenty-six months, 67 vol. per cent. After this time the maximum had been reached and the cells were dead. It formed 5.5 vol. per cent. of alcohol in 15 per cent. dextrose-yeast-water in fourteen days at 25° C.; in a 10 per cent. saccharose solution in twenty days, 0:7 vol. per cent. of alcohol ; in six months, 3 vol. per cent. ; and in twenty-seven months,