This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
The extract which gives the flavor and body to the beer should always be of the first quality and kind. When possible, oils should not be used when extracts can be had (see "Killing of Yeast," later on).
The temperature under which the beer shall be worked is a very important item, and this branch of the art should not be cultivated with less ambition by the enterprising bottler than the one just previously treated upon. If the water or beer mixture is below 100° Fahrenheit, the yeast will not act; a few degrees above one hundred kills the yeast entirely; therefore a thermometer should be used in all cases. Many a batch of beer has been lost by killing the yeast with too hot a mixture. Beer makes the fastest at a temperature from 90° to 95°. In fermenting with white sugar, a higher temperature is required than with brown sugar, molasses or malt, and particularly in cold weather If beer cools down below the point at which it is started, the fermentation is very much retarded; for this reason, small lots of beer, like a gallon or two, are very difficult to ferment, especially in cold weather, and more yeast is required, and a higher temperature in proportion, as the quantity to be fermented diminishes. When the fermentation gets below 45°F. all fermentation ceases. Lager beer is fermented at this low temperature, English ales at 65 to 77° F., because they are designed to be kept for a long time. In fact, all preparations designed to be kept for a lengthy period should be worked the same way. In very large quantities of beer, made with white sugars, from 60° to 75° of heat is sufficient; in very hot weather 50° will answer. With good yeast, the slower the fermentation and the lower the temperature, the longer the beer keeps sweet.
The quantity of yeast required for a batch of beer is a very difficult point to determine, and depends much on the quality and body of the beer, and the temperature of the weather and the quality of the yeast itself. The less taken to secure a good fermentation the better it is. Poor yeast requires more, of course; also small lots of beer require larger amounts of yeast proportionately. Cool weather and fermenting at a low temperature requires also a larger amount of yeast, but good sound judgment, which one can acquire after experimenting for some time, is better than any set rule. One quart of good heavy brewer's yeast to forty gallons of beer usually mixes and works well, but sometimes it may require one-third more or double the quantity. A five-gallon lot, on account of the small quantity, would require nearly a half-pint; as before stated, all depends upon the yeast, the body, the temperature, and the sweetening. The proper way is to keep close track of the temperature of the air in the place where the beer is to be made, and the temperature of the beer, by making good use of the thermometer, and then add what is thought a sufficient quantity, keeping the beer where the temperature will not run down and cool off too fast; and if in four or five hours you see no signs of fermenting, stir up the beer and add a little more yeast, and if it does not work fast enough stir it often.
The time to ferment can only be determined by the condition of the beer. When the bubbles and yeast are coming to the top pretty lively, it had better be drawn off, and put in strong bottles, and the corks tied down. This keeps in the gas, as the fermentation will go on just the same; the beer will then taste smart and lively when the bottles are opened. The bottles should not be put in a cool place or upon ice until a little time has elapsed, as it stops the fermentation, and the beer will be flat and poor. At this stage, the beer can also be put into a strong keg, bunged up tightly, and drawn off through a beer faucet out of the ice-box or with a cooler, the same as ale and lager beer is drawn.
Beer made in hot weather will sometimes be fit to bottle in six hours; but more commonly it requires twelve, and oftentimes twenty-four hours, and even longer, before the fermentation thoroughly commences. Where parties are making beer constantly, it is quite as well to use no yeast at all; this is done by taking some of the old beer, and mixing it with the new, particularly the top or "barm," as it is called.