BREWING 261 and carbonic acid, and to bring the liquor to a palatable condition, and one in which it may be preserved for use. The yeast is added to convert the dextrine into grape sugar, and this into alcohol. No part of the process of brewing requires such careful attention as the fermentation. A certain degree of imperfec- tion in the wort may be remedied to a large extent by skilful fermentation ; but an error in the latter process cannot be corrected. In a space of time varying from six to twelve hours, depending upon the condition of the yeast and the temperature of the wort and of the sur- rounding air, the fermentation commences,
- md'a foam rises in little hillocks to the sur-
face. This foam, which is composed of yeast, gluten, and sugar, made into fine bubbles by carbonic acid gas, appears in this form because the bubbles of acid ascend in separate columns, which are maintained by the motion which has been established in the liquid. The foam be- comes thicker toward the middle of the tun, where it is thickest and rises to the height of two feet or more. After a time the color of the top changes to a light brown, probably the result of oxidation. The fermentation is generally better when this appearance is slight. The disengagement of gas is in proportion to the quantity of sugar converted into alcohol, and the temperature rises correspondingly, or would rise if it were not repressed by passing cold water through a coil of pipe placed in the tun ; this is called the attemperator, and may be used for either lowering or raising the temperature. After a time, varying from 24 to 36 hours, the head of yeasty froth falls, and the newly form- ed yeast becomes more viscid, and the fermen- tation much less active. If it were allowed to proceed without the removal of this yeast, much of it would be precipitated, and, continu- ing to act upon the remaining sugar, would in time convert all of it into alcohol, and finally into acetic acid. It is therefore removed by skimming, and in the best breweries the liquid, or gyle, is drawn oft' into a second fermenting tub, or stillion, as it is sometimes called, and the fermentation allowed to proceed there until the process is completed. Here perfect yeast, formed from the gluten still remaining in the wort, rises to the surface, as a tough, partially organized scum, which is used in the fermen- tation of the succeeding brewing. The pro- cess for strong stock ale is continued for six or eight days, but for lighter ales, such as are called "present use," the time occupied is only four or five days. During the fermentation, from the diminution of the quantity of sugar and the production of alcohol, the fluid becomes thinner, and its specific gravity less ; hence the tormenting process is also called by brewers the attenuation. The temperature rises during the fermentation, so that it may reach 80 or more ; but the more careful brewers, except for special reasons, repress it, and endeavor to keep it below 70. In Scotland the fermentation is often conducted at a temperature below 60, and the process prolonged considerably, occu- pying from ten days to a fortnight. In some breweries an apparatus is attached to the sec- ond fermenting tubs, or stillions, by which the yeast is carried off as fast as it forms. In others, however, it is allowed to remain float- ing upon the surface of the beer until the latter is drawn off. When the fermentation has per- fectly converted the gyle into beer, it is drawn off into casks, for storage or for sale. This is sometimes done by running it into a third tun, called a racking tub, from which, after stand- ing a short time, it is drawn off into the casks. These are then immediately bunged up and kept at a temperature of from 60 to 64. The lighter ales may be drawn for use in three or four days after casking, but the stock ales are stored for six or more months. The tem- perature at which wort is fermented produces not only a difference in the products, but also in the mode in which the process is carried on. The conversion of sugar into alcohol and car- bonic acid proceeds very slowly at a tempera- ture as low as 45 ; but the conversion of sol- uble gluten into insoluble ferment, when acted upon by a like ferment in the presence of air at such a temperature, is effected with facility. The problem solved in the fermentation of Ba- varian beer is the elimination of the gluten and otherazotized matters thatmay bepresent,with- out the conversion of all the spgar into alcohol and carbonic acid, or the conversion of alcohol into acetic acid, and leaving the beer in a condi- tion in which the sugar and alcohol are not lia- ble to further change from exposure to the air. This is effected by a peculiar kind of fermenta- tion, in which the yeast does not form upon the surface of the wort, but falls to the bottom, where it undergoes but little further change, thus leav ing the surface of the liquid freely exposed to the air, by the action of which the soluble glu- ten becomes oxidized and transformed into in- soluble yeast. The reason that ordinary yeast remains upon the surface of the wort is that it is held there by bubbles of carbonic acid, which is generated in great quantity in rapid fermen- tation. The yeast of slow fermentation falls to the bottom because the carbonic acid, disen- gaged from the slowly decomposing sugar, as- cends in bubbles too minute to give sufficient buoyancy. The reduction of temperature al- lows the oxidation of the gluten to proceed more rapidly than the conversion of the sugar into alcohol and carbonic acid, so that before all the sugar is consumed the gluten is elimina- ted and has fallen to the bottom, where it pos- sesses but little power, especially at the low tem- perature at which the wort is kept. This low temperature also prevents the alcohol from pass- ing into acetic acid. If, after all the gluten is thus rendered insoluble and deposited at the bottom of the vessel, the beer is drawn off, it no longer contains any substance which is ca- pable of being converted by oxidation into a fer- ment, and therefore possesses the quality of keeping a long time without becoming sour.
