The fluorine contents of a number of draught and bottled beers from various sources were in the range 0·15‐0·86 p.p.m. and are considered unobjectionable. Of the brewing materials examined, malts usually proved rich in fluorine (< 0·2–11·8 p.p.m.), though barley samples contained < 0·2 p.p.m.; it is suggested that the high values in malts may be due to fluorine derived from coal. However, the bulk of the malt fluorine remains with the spent grains.
Nutrient agar (pH 7·4) was, in general, used for the tests, as wort agar (pH 4·85) allowed excessive growth of yeasts and moulds which suppressed bacterial development. Open exposure of plates to compressed air causes entrainment of organisms from the atmosphere, giving falsely high results. With appropriate shielding of the plates, however, this difficulty can be avoided, though care must be exercised in the choice of shielding device, or low results may be obtained as a result of imperfect deposition; a modification of the Hollaender & Dalla Valle apparatus (Publ. Hlth. Rep., Wash., 1939, 54, 564) is preferred for comparative routine tests. If it is desired to use a filtration method, calcium alginate wool may be used as collecting medium, being thereafter dissolved in sodium hexametaphosphate solution as a preliminary to plating.
Methods of isolating yeast cultures are described, together with the scheme of developing such yeasts in the laboratory, and a detailed account is given of the wort collection and yeast propagation plant. The importance of sterilizing both the worts and the plant before use is emphasized, and the methods adopted to this end are outlined. The technique of collecting the yeast crop is described; worked as a contin uous process, approximately 80 Ib. of yeast can be produced weekly. It is advisable to keep records at every stage of the propagation procedure.
The possible fluoridation of public water supplies as a means of controlling dental caries raises the question of the influence (if any) which such a proceeding would have on yeast and fermentation. Previous work is briefly reviewed, and experiments are outlined to illustrate the effect of varying amounts of fluorine on fermentation, the quantity of fluorine taken up by the yeast, and the possibility of stimulation by very small additions. A comparison is made of two sources of fluorine and the possible cumulative effect at low concentrations is also studied. It would appear that, at the concentration likely to be employed (I p.p.m.), there would be no effect on yeast activity.
The fluorine content of the natural barleys analysed was of the order of 0·05 p.p.m., though this figure was increased by drying; in the finished malt, the fluorine content varied between 0·9 and 12·2 p.p.m., according to the type of kiln. Anthracite coal may contain the element in amounts up to 178 p.p.m., and substantial absorption of fluorine may occur by malt dried and cured on coal‐fired kilns.
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