From the preceding tables we see that the length of time which elapses before the fermentation reaches its acme, supposing this to be measured by the temperature, varies very considerably. The shortest in terval in the table is three days, and the longest nine days; the average of the whole is very nearly six days, which is exactly the mean between the longest and the shortest times. If the reader will glance his eye over the tables, he will perceive that, in general, the higher the temperature of the wort is when let down into the fermenting-tuns, the more rapidly does the fermentation come on. As the worts were cooled by exposure to the greatest cold of the night, and as the coolers were screened from the radiation of heat, the temperatures given to the third column of the preceding tables may be considered as measuring very nearly the greatest degree of cold which took place in Edinburgh at the dates contained in the second column. It follows, as might have been expected, that the warmer the weather the more rapid is the fermentation. And hence the advantage of letting down the worts rather warm in cold weather, and cooling them down as much as possible in warm weather. For this purpose we cannot too much recommend coolers which can occasionally be uncovered altogether, and exposed to the unclouded sky. A roof, perhaps, might be contrived, composed of very light materials, which might be easily slid off, or which might turn upon a pivot. For a roof would be occasionally necessary to screen the worts from rain. In warm weather, brewing should be confined to clear and unclouded days, when the cooling process could be carried farthest of all. We have little doubt that wort might easily be cooled down to the freezing point, if requisite, in our warmest summer weather.
Little can be said about the length of time during which the fermentation of the ale lasts, because it varies very much according to the heat of the weather, and the degree to which the wort has been cooled down. The following table will give some idea of the length of time which elapsed during the fermentations contained in the preceding tables :
8 days. 10
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