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hole series of species of which some are new: he arrived the same general result,
In the following table from Henneberg will be found imerous substances which can be converted into acids by
e various species. The sign+indicates that acidification, - that no acidification takes place.
The variation in shape with the same species, according as the temperature lies near the optimum or the maximum, has been referred to previously (p. 319; cf. Figs. 138, 139 and 140), and also the variation of the iodine reaction of the mucilage.
We have also seen that acetic acid bacteria cause the sharpness of wine and that they only give rise to loss in breweries when a high temperature and free air access are obtainable.
Pasteur (1868) was of the opinion that acetic fermentation was caused by only one species. He worked out a new method for the manufacture of vinegar, to displace the old Orleans method in which the fermentation
proceeded slowly in barrels. As these barrels were employed for several years without emptying and cleansing, large quantities of Vibrio aceti were frequently developed, which caused considerable trouble. The Pasteur method consisted in using shallow vessels instead of barrels; he thus endeavoured to provide the most favourable conditions for the development of the film of acetic bacteria and by this means to bring about as quickly as possible the formation of vinegar so that the Vibrio aceti could not develop. For various reasons the method did not, however, obtain a foothold in practice, partly because the results obtained were so uncertain since here was no question of the application of a selected species or race. In the first edition of his Untersuchungen aus der Praxis der Gärungsindustrie, Hansen had, in this connection, already directed attention to the problem of also applying the pure culture system to the manufacture of vinegar ; but only of late has the way been paved for reform in this direction by the researches of the experimental station in Berlin ; the goal has not yet been reached, however. The question here concerns the most important method
Fig. 143.- Bacterium aceti (Kütz.), Hansen. Young film formation on “double
beer at 34° C. 1999. (After Hansen.)
of vinegar manufacture, i.e., the so-called quick vinegar manufacture of Schützenbach. The acetic bacteria occurring in this connection will be described later.
Acetic bacteria naturally fall into groups according as they possess flagella or not, and according as their mucilage gives a blue reaction with iodine or not. In the following it is expressly stated if the species in question has flagella or gives the blue iodine reaction. The first three following, the descriptions of which are from Hansen, belong to species without flagella.
Bacterium Aceti (Kütz.), Hansen (Figs. 141, 143).—This species forms a smooth gelatinous film on “ double” beer at
C. after twenty-four hours. The film cells are usually r-glass shaped rod bacteria arranged in chains (Fig. ); long rods and threads with or without swellings are y exceptionally found. At 40° to 40°C. long thin eads develop. The mucilage is not stained by a solution iodine or by a solution of iodine in potassium iodide. ter four days at 25° C. it develops colonies on wort latine which are grey, waxy, round, usually arched and ith unbroken edges, seldom star-shaped, and which consist liefly of free, small rod bacteria ; the chain form is repressed ere. The maximum temperature of growth in “ double” eer is about 42° C., the minimum 4° to 5° C.
The species is found both in top fermentation and in bottom fermentation beers; Hansen observed it frequently in the dust of the air and Holm now and then in his analyses of water.
Bacterium Pasteurianum, Hansen (Figs. 133, 138, 139, 140 and 144).—This bacterium forms on “ double” beer at 34° C. after twenty-four hours a dry film which very soon assumes a wrinkled and folded appearance, and rises but little from the surface of the liquid along the sides of the flask. Like those of the foregoing species, the cells are arranged in long chains, but are altogether larger and especially thicker • (Fig. 144). The thread form (Figs. 138, 139 and 140) is
also somewhat thicker at 40° to 40°° C. than with Bact. aceti. The mucilage is stained blue with a solution of iodine or of iodine in potassium iodide. Plate culture colonies on wort gelatine after four days at 25° C. are usually smaller than those of Bact. aceti, otherwise they are the same as with this species. They consist chiefly of typical chains. After about three weeks the surface of the colonies is folded. On wort gelatine and on lager beer gelatine, with and without 10 per cent. of saccharose, the growth is, at 25° C., solid, dry, waxy and yellowish. The maximum temperature for growth on “ double” beer is 42° C., the minimum, 5° to 6° C.
Hansen found this species in the same places as the previous one, but more frequently in top fermentation than in bottom fermentation, breweries. W. Seifert found it in vinegar-tainted wine.
Bacterium Kützingianum, Hansen (Fig. 145).—The film formed on “double” beer after twenty-four hours at 34° C. differs from that of Bact. Pasteurianum by growing high above the liquid along the sides of the flask. It consists of small rod bacteria which are, as a rule, free, or at most joined in pairs ; they form long chains rarely. The thread form at 40° to 40°° C. contains relatively more short threads than Bact. Pasteurianum. The microscopical appearance differs distinctly from that of the latter; on the other hand, both species are alike in that the mucilage is stained blue by a solution of iodine or of iodine in potassium iodide. In plate cultures on wort gelatine this species develops colonies after four days at 25° C., which consist almost exclusively of small, free, rod bacteria; long chains are found only very seldom. The surface of the colonies after three weeks is smooth, not folded. The growths at 25° C., both on lager beer gelatine and wort gelatine, with and ithout 10 per cent. of saccharose, are shiny, slimy an! uish-grey. The maximum temperature of growth is pout 42° C. in “double” beer, the minimum, 6° to 7° C.
Hansen found this bacterium in “double” beer; it i robably diffused to the same extent as Bact. Pasteuriinum.
In addition to the above-cited differentiation between Bact. Pasteurianum and Bact. Kützingianum furnished by Hansen, Henneberg and Seifert have given an extensive series of physiological characteristics, among which, for example, are the following: Bact. Pasteurianum forms a ! most half as much acetic acid as Bact. Kützingianum in lager beer with added alcohol. Thus the former, in lager
Fig. 145.-Bacterium Kützingianum, Hansen. Young film
“ double" beer at 34° C. 1999. (After Hansen.)
beer, with 8 per cent. of alcohol, produces 3.23 per cent. of acetic acid in twelve days, while the latter forms 6:56 per cent. ; the formation of acid by Bact. Pasteurianum is likewise only half as great as that by Bact. Kützingianum when the cultivation takes place in a 2 per cent. glycol solution. When yeast water with 3 per cent. of dextrose is used as the nutrient solution, the growth of Bact. Pasteurianum at 26° to 30° C. consists of long chains, that of Bact. Kützingianum, on the contrary, of single cells, or pairs connected together. The same microscopical differences are thus found here as between the growths of both species on beer and wort gelatine.
Of the many species of acetic acid bacteria which have