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The decomposition products of bacteria are of many cinds. They can develop acetic acid, lactic acid, butyric cid, various alcohols, etc. A large number liquefy nutrient gelatine through the possession of peptonising power.
Pasteur had discovered in the year 1861 that butyric acid bacteria are anaërobic, that is, they can only grow in the absence of oxygen. The majority of species, however, thrive best with free access of air. The acetic acid bacteria are typical examples of aërobic forms.
Pasteur (1876) was also the first to point out the injurious part played by bacteria in the fermentation industry. The disease phenomena brought about by bacteria in fermented liquids are: mucilage formation, decolorisation, turbidity, acid formation, disagreeable smell and taste.
Pasteur gives some information on mucilage formation in beer and wine ; he mentions a Micrococcus which makes the liquids mentioned ropy. Kramer isolated from thick wines a Bacillus with which he could induce the same disease in sound white wine. From ropy Belgian beers, van Laer isolated bacilli which were the cause of the disease. L. Vandam also found in English beer a Bacillus that makes it thick. At the same time this species only attacks the beer when present in large number at the beginning of the primary fermentation. Brown and Morris describe a Coccus, likewise causing ropiness in English beer. The disease attacked the beer when it was six weeks to two months old. The source of infection appeared to be a slaughterhouse for pigs in the neighbourhood of the brewery. A Pediococcus was found by Lindner in ropy “Weissbier”.
The disease known as the turning of wine consists in red wine assuming a brown colour, while white wine becomes turbid and discoloured and frequently develops a dark colouration. The tartar occurring in wine is changed by this disease into potassium carbonate, which causes the change of colour. Kramer isolated two Micrococcus species from turned wines.
The bacteria of lactic acid, butyric acid and acetic aci may be mentioned as acid producers in fermented liquiis. In breweries the first are especially active in the mashing stage. According to van Laer a species, Saccharobacius Pastorianus, causes the turning of beer; the beer thereby loses its brilliancy, becomes disagreeable in smell and taste and forms a sediment; the latter consists partly of nitrogenous products which separate as a result of lactic acid production, and partly of the bacteria themselves. Bacillus acuti lactici, according to Kramer, causes the “ Zickenwerden " (see p. 343) of wine. Butyric acid bacteria are responsible for a very unpleasant smell and taste in beer. They are especially injurious in the mashes in distilleries.
Acetic acid bacteria are found particularly in wine manufacture, where they occasion the tartness of the wine. When once the wine has been strongly attacked by them, and is in consequence vinegar sour, it is valueless ; there is then no means of removing the evil. In brewing they are of most danger in top fermentation breweries, where the conditions for their development are more favourable than in bottom fermentation breweries. Hansen experimented in practice with Bacterium aceti and Bact. Pasteurianum in the presence of Carlsberg bottom yeasts No. 2 and No. 1. He came to the conclusion that the bacteria in question were indeed present in the finished lager beer if the infection took place at the beginning as well as at the end of the primary fermentation, but that this infection appeared neither in the fermentation cellar nor in the lager cellar. The bacteria can propagate themselves only after the lagered beer is drawn off; the beer, however, did not become vinegar sour if care was taken that the transport vessels and bottles were well closed and well filled. The same holds good
also when the bacteria are introduced into bottom fermented beer after it has left the lager cellar. The infection generally occasioned no bad effects when the precautions named were observed. High temperature and free air access are necessary for the development of the bacteria.
Gayon and Dubourg found in wine containing mannite, a short non-motile rod which forms masses of zooglea. It reduces invert sugar to mannite. Wine, however, is most exposed to this disease in warm climates. (As formerly mentioned, Penicillium glaucum can cause the same phenomenon.)
According to the investigations of V. H. and L. J. Veley, the disease of rum, called “faultiness,” is brought about by a bacterium which these authors name Coleothrix methystes. This species is especially distinguished by its great power of resisting alcohol, the bacteria retaining life in rum with an alcohol content of 75 per cent. by weight.
Pediococcus or Sarcina species frequently occur in breweries. However, only certain of these cause harm, and these only under special conditions. It has been shown by Hansen, Jörgensen and Ant. Petersen that when certain of the species occur even in considerable amount in beer, they are without appreciable influence on its quality. These forms have been especially studied by P. Lindner (1888). According to him and other authors, some species under certain conditions occasion “sarcina turbidity”. In this connection Reichard states that the disease appears when a strong afterfermentation takes place in beer inoculated with Sarcina, while equally strongly infected beer did not succumb to the disease when the primary fermentation was a strong one, so that in place of the vigorous after-fermentation, only a slight maturing took place. An addition of hops to the lager casks will, according to the same author, prevent an outbreak of the Sarcina disease.
Schonfeld has also investigated the infection of yeast br Pediococcus and Sarcina. His results are the following Culture yeasts are susceptible to Sarcina in varying degree. Wild yeasts are more prejudicial to the development of Sarcina than culture yeasts ; with favourable conditions a Sarcina acclimatised to any yeast race can spoil the beer prepared by means of this yeast; Sarcina is more anaërobie than aerobic; the virulence of Sarcina is dependent upon certain medium temperatures, an absence of air, and on motion ; the multiplication of Sarcina is restricted by strongly hopping the beer, by high alcohol content and by aeration.
Kupfer seeks for the causes of the poor “ head" and slight stability of beer in Sarcina infection.
S. v. Huth has recommended the employment of a tartaric acid remedy for Sarcina, in which 6 grams of tartaric acid are added in aqueous solution to every kilo of yeast. After stirring, the whole is put on one side to rest for six to twelve hours, after which the mixture is introduced into the fermenting vessel. This method must always be applied with care, and is only to be recommended when the stock yeast contains practically no wild yeast. For if this is not the case the latter develops at the expense of the culture yeast, and the result proves correspondingly unfavourable.
5.--APPLICATION OF BACTERIA IN THE ALCOHOLIC FER
MENTATION INDUSTRIES. Only the lactic acid-forming bacteria are directly employed in the alcoholic fermentation industries, these being applied in distilleries in subduing butyric acid bacteria and in the “ Weissbier” breweries. In breweries the yeast settles to the bottom of the dilute wort; such does not happen in distilleries, where the thick mash does not allow of this.
The pitching yeast is therefore produced by itself in special vessels. The requisite amount of nutrient liquid for this is acidified in order to prevent the development of harmful germs, such as butyric acid bacteria, which are unable to thrive in strongly acid liquids. A strong and suitable formation of acid is therefore effected by the addition of a young and vigorous pure culture of lactic acid bacteria. The latter is obtained by starting from a trial mash of which the souring is satisfactory. The optimum temperature for lactic acid bacteria lies at about 50° C., that of butyric acid bacteria, on the other hand, at about 40° C. The sweet yeast mash is therefore kept at about 50° C., in which case only a strong growth of lactic acid bacteria develops. When the degree of acidity is sufficiently high, the lactic acid bacteria are killed by warming the mash up to 70° C., following this it is quickly cooled to 17° to 20° C., and a pure culture of a selected yeast race added. A part of the yeast produced is then taken out to be used in pitching a fresh portion of sweet mash.
As formerly mentioned, F. Lafar was the first to introduce the systematic selection of a lactic acid bacterium for this purpose. Wehmer, however, has lately attempted to suppress butyric acid bacteria with commercial lactic acid, which, according to his investigations, has given good results.
Of the remaining bacteria referred to, those of acetic acid are employed, as is well known, in the manufacture of vinegar.
Ferd. Cohn showed that bacteria are plants, and set up a system based on cell form. We have seen, however, that the same species can assume various forms of growth.
For the investigation of different species, the morpho