THE BAKERS' GUIDE

effort on the part of the yeast cultivator to produce a yeast as free as possible from any admixture of these wild types and other disease germs.

The disease-organisms are small rod-like, or thread-like bodies, and much smaller in size than the yeast-cells, and more difficult to observe, so that a magnifying power of not less than 400 diameters, with glasses capable of the best definition, are necessary. It is better to employ objectives with a magnifying power of 750 to 1,000 diameters. Were these disease-organisms absent, acetous fermentation could not take place.

Yeast-cells may be diseased without being putrid^ and they may be unhealthy without being diseased.

Yeast may become unhealthy, even when not diseased, by being grown for too long a time in a liquid deficient in mineral food; fermentation is thus languid, and those objectionable organisms, the filamentous ferments, may gain the race in the production of alcohol or acid.

Damp yeast loses its activity at or about 128 degs. (Fahr.).

Cleanliness of the fermenting vessels is obviously of import- ance, because otherwise other ferments than the alcoholic may easily cling to the sides, and so induce an acid or putrid fermen- tation; this is particularly the case with Bacterium ter mo. On this account it is of importance to have the fermenting vessels con- structed of some material which is easily cleansed.

Yeast may be inherently bad when its cells are faint or oldt or it may be bad through the presence oj foreign impurities \ or it may become bad in keeping.

The Appearance of Weak, Exhausted) and Impure Yeast-

Referring to weak and exhausted compressed yeast, it looks dull and leels soft and sticky to the fingers, or breaks up into small warm crumbs, not breaking with a free, clean, fracture ; the smell of it will not be that of sound acid fruit, such as apples, but that of tainted meat or flesh. If the yeast has been stored for a day or so, it will feel to the hands, and show by thermometer, warmer than the atmosphere where it has been stored. In proportion as it is warmer will it be bad. These are sure tests for soundness or un- soundness of yeast, and no microscope is needed. But to detect impurities and their nature involves microscopic work, and will require careful, watchful attention and practice. When looking at yeast through a microscope, if it is seen to have inside the cells a number of dark specks, and the outer skin has a crinkled, shrivelled appearance, it has become too exhausted to properly do its work ; or if the yeast has scattered amongst its cells a number of organisms like short pieces of thread

1HE BAKERS' GUIDE.

or other germs, not round or oval, which is the shape of the true yeast, it is then unfit for bread-making, and contains impurities in the shape of bacterial organisms, that the brewer or distiller by careless workmanship has permitted to get in it from the air And from unclean utensils. The ordinary common-place collector of yeast in the brewery is unmindful of the baker's need, he merely collects so much weight, that will fetch his firm so much per pound ; the baker's safest plan is to have nothing to do with him, but buy only high-class yeasts. If compelled to use faint or impure yeast — because you cannot get any other — use nearly double the quantity of yeast, and don't expect too much work from it ; be content with small sweet bread, obtained from a quick fermen- tation at a temperature of about 90 degs. (Fahr).

It must be as true of yeast as of all other life, that there is a condition of growth more suitable to it than any other. Ascer- tain, therefore, what are the most suitable surroundings for healthy yeast life and reproduction, and then never depart from these conditions, whatever the pressure. The one great reason for this is, that science and observation both endorse the statement that, as soon as a medium becomes unhealthy for yeast, it becomes healthy for the growth of one or the other of the disease germs, and that these germs lie dormant when the conditions are .opposed to their activity, and even when they may live in these unsuitable conditions, their growth and reproduction is nothing worth noticing ; but when the conditions are favourable, they .are then set completely free and multiply very quickly. This is as true of lactic and butyric germs as it is of all kinds of yeast. Every form of life has its sphere and food. Neither moths, mush- rooms, nor flies will germinate in brine, or quicklime, and though they may pre-exist in some form, they must have a medium as a matrix in which to develop and reproduce their species. The .cheese affords a matrix for the cheese-mite, or it would remain undeveloped and devoid of a means to mature and reproduce itself. This is the great truth I would have you learn. No matter how low we descend, it still holds good through all forms .of microbic life the same. In just so much as these microbes differ in their nature, so much will they differ in the suitability x)f the medium of their sustenance and life. A smelt and a tad- pole will not thrive equally in the same surroundings, therefore ascertain the physical laws governing the healthy reproduction of yeas

Before yeast can obtain any food from flour, the flour must be made into a thin paste, as already shown ; yeast cannot assimi- late dry or solid food. There must also be a certain amount of heat. In a baker's ferment or sponge both these conditions are

THE BAKERS' GUIDE,

present. The flour is stirred into warm water, which dissolves out the sugar and soluble albuminoids. The yeast commences to act upon these, and, with the aid of a natural principle, like human gastric juice, within itself, it proceeds to use the natural sugar in the flour, and to alter these soluble albuminoids and the starch into sweet substances or amides. These are its natural foods, which it assimilates from the sponge. It absorbs these substances into its own elements, and gives off carbonic acid gas and achohol.

Note, — There is practically no alcohol formed in the earlier stages or until the free air or oxygen of the sponge or dough is exhausted, and by taking a rapid sponge in first turn, or dough- ing direct and turning the dough often, there will be plenty of free oxygen present and very little alcohol. You know the feel of -well-aerated, well-made dough. This making and turning, or 41 heading up, saturates it with free oxygen. Alcohol is a poison to the yeast. The evolution of gas and alcohol is in proportion to the amount of nourishment it has been able to absorb. There is also a series of other changes going on during bread fermenta- tion. The heat and the moisture are also acting upon the in- soluble albuminoids of the flour, disuniting, changing, and de- grading. During the whole operation the yeast will, while re- taining its vigour, continue to seek out and digest the mineral And nitrogenous matters it needs or can get at.

Beer Yeast is collected from a number of picked breweries in London and the provinces, the various brews thus collected being blended with a view to combining strength, uniformity, and security ; but uniformity of action has not been attained, as this yeast is prone to grow faint, and sometimes to entirely collapse in hot weather.

Mode of Working. Put in a ferment with i of the total -water at 84 degs., a handful of flour and some other yeast food, allowing one pint of yeast to every 140 lbs. of flour to be made up. Let this ferment until fermentation begins to subside, and then strain it into the trough and add half of the total water at a heat sufficient to bring the added flour up to 86 degs. Stir to alight spongy sponge, and allow to ferment six more hours, and until it lias risen and subsided twice ; then add the remaining half of water at a heat sufficient to bring the heat of dough up to 86 degs., and 3 £ lbs. of salt ; break the sponge and this added water up to- gether quite smooth, and then make the whole into dough, •which should rise for about two hours, and then be taken out of trough, scaled off, moulded and baked.

Types of Yeast