After two hours have elapsed at 100% reflux, the system is in equilibrium, and the top section filled with the foreshots. You need to collect this product very slowly, (1-2 drops per second), so you will not disturb the equilibrium. You must proceed cautiously at this stage, because there is only a small quantity of the foreshots and it would be easy to disturb the small zone they inhabit in the top of the column. You will begin collecting them at a temperature as low as 60°C (140° F), and as they are collected, the temperature will slowly rise. Discard them until the vapor temperature stops rising, and then begin collecting the heads, which may be added to the next batch for ethanol recovery. By this time, the temperature should be stable at about 78° C (173° F). You can expect 100 - 150 ml of heads from an average batch. Your nose should be the best judge of when the heads have all been collected, but if you wish to be absolutely sure (or if you have a cold!), collect 250 - 300 ml (about a cup).
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