Sprinkle on the yeast. Tie a cloth or secure a sheet of polythene with elastic over the vessel to keep out the flies. The ideal temperature is 65-75 degrees F., that is, about the range of a room in summertime. Cooler temperatures mean slower fermentation. This is no advantage in beer-making: it merely holds up regular production, so find a warm corner for the brew, or else use some simple heater, in cold weather. A thick foam builds up on the surface within 24 hours; skim this off. It contains impurities which may make the beer slow to clear. Thereafter leave the brew in peace till the yeast has done its work.
With strong beers, however, it is advisable to add the sugar in two doses, or they occasionally "stick" at 1020 or so.
Strong beers take about a week to ferment out, weaker ones three days or so. The hydrometer will tell you the progress. But when the gravity gets low you cannot be sure at what point it is merely telling you about unfermentable solids left in suspension. Your aim is to decant the beer as soon as it is "flat," since the decanting while the ferment is still on can lead to burst bottles. Best then, to watch the surface of the brew. Towards the end of the ferment the bubbles collect in a ring at the centre. Then the surface, which is cloudy while the yeast is till active, begins to clear. This means that the yeast has no more sugar to work on, and is beginning to sink down. Then is the time to bottle.
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