Beer-stripping is not absolutely essential and theoretically it would be quite possible to fractionally distil the beer itself. However, beer-stripping has a number of advantages. The chief is that the alcohol is concentrated into a relatively small volume in a relatively short time and quite a few of the impurities eliminated. It would be extremely tedious to fractionally distil all that beer at 4 ml per minute (it would take about 8 days). Also, the yeast is left behind and does not interfere with the more exacting fractionation process. A further, and very practical consideration, is that the purer and simpler the mixture of chemicals to be separated the purer the final product, so the more rubbish one can get rid of during beer-stripping the better.
We have 50-60 litres of beer which need purifying but the boiler of the still has a maximum volume of just 25 litres. It is important not to put too much beer in the boiler because it foams quite a lot and liquid would foam up into the bottom of the column and be swept over into the collection bottle by the rush of vapour. About 60% full is suitable which, with a 25 litre boiler, means about 16 litres. So we have to strip the beer in three separate 16-17 litre batches.
Proceed as follows: Run 16 to 17 litres of beer into the boiler, start the flow of cooling water, switch on the boiler and open the collection valve WIDE. Under these conditions there is very little reflux so, to some extent, the still is operating like a pot still. This is what we want for beer stripping. If you are using 750 watts it will take about 2 hours to come to the boil., and when it does liquid starts to drip quite rapidly into the collection bottle.
The temperature of the vapour coming over from the boiler at the start will be about 80 deg. C. and will rise to 96+ deg. C. or so as the ethanol in the boiler becomes exhausted. This will take about 21/z to 3V2 hours at 750 watts. You will have collected about 3 litres of high wine. Although there will be some ethanol remaining in the boiler at this point, the amount will barely be sufficient to warrant the cost of the electricity to drive it over, but you can continue to 98°C. or so if you wish.
There are two possible ways to judge when beer stripping should be terminated — the volume of distilate collected and the temperature of the vapour. Always use the latter, the vapour temperature, regardless of the volume of distilate collected.
Allow the boiler to cool somewhat before opening the bottom valve and sending the contents to drain. Then add the second and third batches of beer and strip them just as you did the first. You will have collected about 9 litres of high wine with a strength of around 50% alcohol.
Drain and flush the boiler and then add the high wine plus several litres of water to raise the volume to 15 litres or so. There are two reasons for this: one is to ensure that the heating element is still covered with liquid at the end of distillation, while the second is because a purer alcohol is obtained when distilling from a dilute alcohol solution than from a concentrated one. We are now ready to carry out the important second stage of fractional distillation.
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