INDUSTRIAL APPLICATION OF BACTERIAL ACTIVITIES Baking.—The proper regulation of the fermentation which takes place during the raising of the dough is one of the most im portant problems of bread making. To-day this fermentation is artificially induced, in the making of the wheaten loaf, by the addition of suitable types of yeast—bakers' yeast—and by shorten ing the time of dough raising, the varied micro floret of the flour is purposely prevented from taking part in the process. In those types of bread where the dough fermentation is induced by the addition of barms, the normal flora of the flour still plays an active role. The use of barms however is restricted to-day almost exclu sively to the making of rye bread.
Bacterial Decomposition of Starch and Sugars.—Leaving out of consideration the old established industries of brewing and wine making, there is a very large number of other processes by which the starch and sugar decomposing enzymes of bacteria— and of yeast—can be utilized for the production of industrially important products.
By employing certain bacteria, known as lactic acid bacteria, sugar solutions can be made to undergo another type of fermenta tion which results in the accumulation of very high yields of lactic acid. The fermentation has been industrially exploited since the middle of the I gth century, but only comparatively recently have efforts been made to conduct it under aseptic conditions, so as to avoid undesirable secondary fermentations which frequently seriously reduce the yields, and in the presence of pure cultures of the most suitable bacteria.
A diagram of a plant suitable for the aseptic production of lactic acid, and of many other types of fermentations, under semi-continuous conditions, is shown above.
Apart from the use of sugars, such as molasses, for the pro duction of power alcohol, recent investigations have shown that certain sugars, pentoses, which cannot be fermented by yeast, can be converted by bacteria into a mixture of ethyl alcohol and acetone. These sugars occur as a condensation product in a very large number of plants and are available in many parts of the world, notably in tropical and sub-tropical countries, in the waste products from agricultural industries. A fermentation process has recently been developed for the production of power alcohol from pentoses, and it is claimed that as much as 20 imperial gallons of this liquid fuel has been obtained in this way from one ton of waste.
Many other fermentation processes, involving in these cases the breaking down of hemicelluloses and of cellulose, are of considerable industrial importance, the preparation of synthetic farmyard manure, for instance, and the production of natural indigo, but space does not permit to discuss them in detail. They have been dealt with in considerable detail by Thaysen and Bunker.
Bacterial Decomposition of Organic Nitrogen Com pounds.—Apart from the dairy industry, which may perhaps be most conveniently classed under the above heading, though the activity of bacteria in milk involves both its sugar and its casein content, the bacterial decomposition of organic nitrogen com pounds may quite conceivably become of economic importance in the future in other directions—in the degumming of natural silk, for instance, and in the synthesis of nitrogen compounds which are costly to prepare by chemical means. Ehrlich has drawn atten tion to such cases, among them the preparation of an important part of the essential oil of roses.
It has been suggested that certain sulphur bacteria might be used for converting naturally occurring zinc minerals into zinc sulphate under conditions which would render the zinc more easily recoverable, and recently observations have been recorded that the inert gas argon had been detected in yeast during the fermentation of sugars.
The Destructive Activity of Bacteria in Industry.—How ever desirable the utilization of bacteria may be, it is still more im portant, sometimes even essential, to arrest and to prevent their activity in many industries. In the textile industries, for instance, damage involving millions of pounds yearly is caused through the destruction and mildewing of fibres and fabrics. In the wood industries equally serious losses occur through the action of micro-organisms, chiefly of fungi. In the sugar industries the freshly pressed juice is often inverted by bacteria and the crystal lization of the sugar rendered difficult. In dairying, and in many other industries too numerous to enumerate, serious destruction by bacteria is frequently recorded.