one-fifth of the quantity originally present. At first they contained, on an average, 45 lbs^ per barrel of saccharine matter. The spent washy after distillation, contained still 9 lbs. per barrel. This liquor was capable of being fermented a second time, and of yielding more spirits.
But as these worts were very weak, and as they were fermented in very advantageous circumstances, and in much greater quantities than either Lavoisier or Thenard could have employed in their experiments, we do not conceive that more than four-fifths of the sugar which they employed in their experiments could have been decomposed. Now, if to the carbonic acid actually developed in their trials we add a fifth part, the number will approach very nearly to the one which we have deduced from the supposition that sugar is decomposed by fermentation into> an integrant part of alcohol and an integrant part of carbonic acid.
On comparing the quantity of alcohol of 0*825 obtained in our experiments from the quantity of saccharine matter actually decomposed by fermentation, the result was, that 100 parts of saccharine matter yielded almost exactly 50 parts of such alcohol. This would amount to about 40*9 parts of real alcohol. There can be no doubt that a portion of the alcohol was lost during the distillation, which was conducted in the rapid way followed some years ago by the distillers in Scotland. If we suppose one-fifth to have been lost, which is probably not much beyond the truth, the real produce of alcohol from the saccharine matter of malt would be almost exactly one-half of its weight, which it ought to be, according to the preceding supposition that it is decomposed into alcohol and carbonic acid.
When the fermentation is languid, it is customary to beat in the yeast which has collected on the top ; that is to say, the whole is stirred till the wort and yeast are thoroughly mixed.
In practice it may be observed, that the two methods of fermentation in brewing ales by putting the worts to the yeast at high and low heats, is worthy of the brewer's attention who desires to produce ales of the finest quality.
In slow fermentation, the degree of heat at which the wort is pitched is from 50° to 55°. When the gyle comes to a head, the yeast that forms on the surface is beat in, and this process continues from nine to twelve days. When the ale is judged to be sufficiently attenuated, it is run from beneath the yeast into barrels.
In quick fermentation, the wort is mixed with yeast at from 60° to 65° of heat. The yeast is allowed to form on the head of the gyle, and gives out carbonic acid until it begins to turn viscid, and tends to sink down through the wort. This takes place in from thirty-six to forty-eight hours. It is then mixed well in the gyle, and run into barrels, where it ferments, and works over for forty-eight hours, requiring to be regularly filled up at first every two hours, for the first twelve hours, then every four hours, until it gradually comes to yeast, and ceases working out of the barrels.
Thus there are two distinct methods of fermentation. The quick fermentation is that by which porter is made, and ale generally, throughout England. The slow fermentation is the practice in brewing ale in Edinburgh and in Scotland. In both methods, the decomposition of the glueosin, and the formation of alcohol* go on until the ale is finished, and either run into barrels, sis in Edinburgh, or until the fermentation ceases in the barrels, as in England. This latter is the proper term for cleansing. English brewers, in general, know nothing about attenuation. Their practice of fermenting at a higlt heat forces on the gyle so rapidly, that as soon as ready, which is within 48 hours, they must run the wort into barrels, to check the heat and bring it to cleanse into yeast, which does not begin to form until 12 or 14 hours after the wort is first run into barrels. The repeated filling of the barrels as the wort flows out, being equivalent to the beating in of the head of the yeast for some days by the Scotch brewers.
Edinburgh brewers attenuate their high-priced bottled ales as low as they can carry it with safety, for the purpose of making it keep. The weak draught ale is not attenuated so much. This gives it a fulness to the taste.
In the year 1835, a practical treatise on brewing and storing of beer was published by Mr William
Black. This book, as Mr Black informed us, was the result of forty years' experience as a practical brewer. It contains many sensible observations. His thepry of fermentation is imperfect, from the state of our knowledge. The souring of ale during its fermentation, which sometimes takes place, he ascribes to electricity. I have never had an opportunity of verifying or refuting this opinion. Should it be true, the souring ought to be prevented by forming a communication between the fermenting beer and the moist ground, by means of a copper, brass, or iron wire.
Mr Black considers, that when the first mash is judiciously made, the temperature of the water for the second mash is of very little consequence. He says of the heat of the worts, as they flow from the first mash, any temperature between 138° and 152° will answer, and recommends, as a good mean for pale beer, 145°. For brown beer the temperature should be from 138° to 145°, and to obtain these heats, that 175° for the first mash of pale malt will generally make the worts flow within the given range ; and 160° to 165°, for brown beer, will do the same.
5. The last step of the process of brewing is called cleansing. When the violence of the fermentation is over, the head of yeast which covers the top of the fermenting-tun diminishes in height by the gradual escape of the carbonic acid gas, which heaved it into bubbles. If the wort were allowed to remain in the gyle-tun after this has happened, the yeast would again mix with it ; and the consequence would be a disagreeable bitter taste, known among brewers by the name of yeast bitter. The fermentation would likewise continue, though in a languid manner, and the ale would soon run into acidity. These accidents are prevented by drawing off the ale into small casks. And this is called cleansing. The casks are filled quite full, and left with their bungs open. The drawing off of the ale from the gyle-tun lowers its temperature, and, of course, checks the fermentation. On this account the cleansing is sometimes practised in summer when the elevation of temperature in the wort is at its height.
We have repeatedly observed a curious circumstance during the cleansing, not very easily accounted for. If we take the temperature of the ale at the upper surface of the gyle-tun, and then observe the temperature of the ale when it flows from the stopr cock at the bottom of the tun, we shall generally find it one or two degrees hotter in this latter place than at the former. We ought naturally to expect the highest temperature at the top of the gyle-tun.
The ale still continues to ferment after it is put into the small casks; but as these casks are always kept full, the yeast, as it comes to the surface, flows out at the bung, and thus separates altogether from the beer. It is this separation that has induced brewers to distinguish it by the name of cleansing. In these casks, then, the yeast divides itself into two portions. The greatest part rises up with the carbonic acid evolved, and flows out at the bung-hole; while another portion subsides to the bottom, and constitutes what is called the dregs of the beer. It is essential to the cleansing that the casks should be always full, otherwise the yeast will not run off, and the beer will not become transparent. This object is accomplished -in small breweries by a man constantly going round, and filling up the casks as they work down. But in the London breweries there is an ingenious mechanical contrivance which answers the purpose perfectly.
When the fermentation has subsided, the beer will in general be found transparent. It is bunged up in the casks, and preserved for sale; or in London, where the quantity is too great for this, the beer is removed into large stone vats, capable of holding several thousand barrels, from which it is gradually distributed to the consumers.
In London, where the beer is usually sent to the public-houses as soon as the fermentation is over, and before it has had time to become fine, it is usual to send along with it a quantity of finings, as it is called, that is, a solution of isinglass in weak sour beer, made from a fourth mash of the same malt. The publican puts a certain quantity of this into every cask. It forms a kind of web at the surface'of the liquid; and, gradually sinking to the bottom, carries with it all the fiocculent matter, and leaves the beer transparent.
We shall terminate this chapter with a table exhibiting the results obtained by brewing with malt made from a considerable number of different varieties of barley and big.
GRAIN. First Qualify.
Weight per Bushel, lbs.
Bushels of Malt used.
Weight of Malt per Bushel, lbs.
Wort in Barrels.
Specific Gravity of Worts.
Lbs. per Barrel of Dry Extract.
Total Quantity of Dry Extract.
Solid Extract from a Bushel of Malt in lbs. Avoirdupois.
Solid Extract from a Bushel of Raw Grain.
Solid Ex-tract from
50*375 50*375 50-375 50-375
Was this article helpful?