As a practical matter the purification of beer by distillation is carried out in two stages. The first stage is known as beer-stripping and consists of a crude, rapid distillation in a pot still to contain the alcohol and impurities in a smaller volume. This smaller volume is then purified much more slowly and carefully in the second stage of fractional distillation.
Beer-stripping: Beer-stripping is not essential and if one wished to avoid the expense of the equipment required 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 and impurities are concentrated into a relatively small volume in a short time. Also, the yeast is left behind and does not enter the more delicate fractionating still. A further advantage is that the crude alcohol solution will be sterile after beer-stripping and therefore can be safely stored for short periods pending fractional distillation if this is required for some reason.
As discussed in the equipment section, an inexpensive beer-stripper can be made from a 30 US gallon (113 litre) domestic hot water heater (see Figure 2). If the fermenter is mounted on blocks the beer can be transferred to the stripper by gravity flow via a short length of rubber hose. For complete drainage it is only necessary to ensure that the bottom of the fermenter is higher than the final liquid level in the stripper. Any beer in the hose can be driven over with a little water poured in from the fermenter end.
With the beer in the stripper, close the bottom valve, start running cold water through the condenser, and turn on the electric current. You will be collecting about 16 litres of distillate so have several large plastic bottles ready to receive it. An even better arrangement is to run the output from the beer-stripper directly into the fractional distillation boiler, using a funnel and a length of rubber hose. With a 3000 watt heater the 50 to 60 litres of beer will come to the boil in about 2 hours and liquid will then start to drip from the condenser.
The temperature of the vapour coming over from the boiler at the start will be about 80 oC. and will rise to 98 to 100 oC as the ethanol in the boiler becomes exhausted. This will take about 21/2 hours. Although there is still a little ethanol remaining in the boiler at this point, the amount will be too small to warrant the cost of the electricity to drive it over.
Allow the boiler to cool for a few hours before opening the bottom valve and sending the contents to drain. Run a little water through the boiler to flush out as much of the dregs (probably containing a little yeast) as possible.
Fractional distillation: This is the most important step in the whole process of producing pure alcohol from sugar. And an essential step. Any description of alcoholic beverage production which does not include it is describing the production of an impure product, a moonshine. It may be palatable but it will certainly not be pure alcohol.
Because of its importance it will be described in some detail, a detail which unfortunately may be intimidating to some and boring to others. To those in the first category we say this: Once you have assembled the equipment and made a few runs it will all become incredibly routine. It's like riding a bicycle a lengthy description of how to do it would probably decide you to take up walking instead, but once you've set off down the road there's no looking back. It's easy!
The 14 to 16 litres of impure alcohol produced by the beer-stripper is now in the boiler of the fractional distillation apparatus illustrated in Figure 3. The boiler, which is an apartment-size hot water heater with the thermostat removed, can be obtained with a capacity in the 7 to 10 US gallon range (25 to 38 litres) and consequently can easily accommodate the entire output of the beer-stripper. The column is insulated in order to maintain a steady temperature regime within the full length of the column during the many hours of operation.
Note that the top of the still-head is completely open to the atmosphere and not sealed. This means that there is no pressure in the still and no danger of an explosion. No vapour can escape through the open top of the column and still-head because the cooling coil is very effective in converting the vapour to liquid, which then runs back down into the boiler.
Cold water is run through the condenser in the still-head and power supplied to the boiler. At the start the small valve in the horizontal part of the still-head is closed so that all the vapour condensed at the top will run back down the column. Under these conditions the column is said to be operating under "total reflux".
Keep an eye on the operation until the thermometer in the still-head suddenly rises and you know that the hot vapours from the boiler have heated the column and its contents and have risen into the condenser where they are being cooled and converted back to liquid.
The boil-up rate must not be greater than the column can handle. A packed column provides only a limited path for liquid to flow down against a rising stream of vapour so, if the boil-up rate is excessive, the column will choke with liquid and become ineffective. This should not be a problem with the 11/4 inch diameter column and the type of packing described in the equipment section, especially if the heat input is reduced to 750 watts by changing or controlling the immersion heater in the boiler as recommended.
The next several hours are spent equilibrating the column. This is the period during which the various components of the mixture sort themselves out with the more volatile components moving to the top of the column and the least volatile moving to the bottom. Don't omit this step because it is quite important.
TEMPERATURE PROFILE us TIME
DRAW OFF 'HEADS &
TEMPERATURE PROFILE us TIME
DRAW OFF 'HEADS &
Switch on Switch off
The progress of equilibration can be followed by watching the temperature of the vapour at the top of the column. Ethyl alcohol has a boiling point between 78 and 79 oC., the exact figure depending on the atmospheric pressure, while the heads have a lower boiling point. The thermometer will register this and a temperature as low as 70 oC. may be observed. Periodically open the valve in the still-head a fraction to bleed off these heads into a receiver, leaving room for the ethanol to rise a bit higher in the column. A suitable withdrawal rate would be 2 or 3 drops per second.
You will notice that these heads have a terribly pungent smell and you can congratulate yourself that you won't be drinking them. They are highly inflammable and make an excellent fondue fuel or starter fluid for the barbecue. As the heads are bled off the temperature will slowly rise to a value just above 78oC*, indicating that most of the heads have now been drawn off and ethyl alcohol is beginning to appear. A word must be said here about the accuracy of thermometers. A thermometer purchased from a scientific supply house should be accurate to 0.1 oC. but don't count on it. Thermometers purchased at a drugstore or a winemaker's supply store can be off by as much as 2 degrees. We recommend that you always check the accuracy of a thermometer by placing it in boiling water and recording the temperature. You may be lucky and find you have purchased one which reads 100 oC. but if it doesn't, simply make a note of the deviation and apply the appropriate correction whenever you use it to read a temperature.
Fortunately for us it is not necessary to rely on the exact temperature during a fractional distillation in order to indicate when the heads have finished coming over and it is safe to start collecting ethanol. Constancy of temperature is sufficient. Thus, if the temperature has risen to just over 78 oC. and has stayed there for 15 minutes or so you can be fairly sure that the heads have pretty well finished.
*Footnote: The ethanol/water azeotrope has a boiling point of 78.14 oC. at the standard atmospheric pressure of 760 mm Hg. This changes with a change in atmospheric pressure. The B.P. of pure 100% ethanol is 78.4 oC at standard atmospheric pressure.
Briefly then, proceed as follows: Operate under total reflux for several hours to equilibrate the column, bleeding off the heads periodically until the temperature remains constant between 78 and 79 oC. Then start to collect the distillate by opening the valve in the still-head. A diagram (not to scale) is provided in Figure 10. to illustrate the sort of changes in temperature to expect from the moment the apparatus is switched on to the moment you switch off and start to clean up.
Collection rate: In simple distillation you collect everything which vaporizes from the boiler, but in fractional distillation you collect only 10% of it. The reason for this is as follows:
The efficiency of a fractionating column in separating liquids of different boiling points is dependent upon two factors. One is the length of column and the type of column packing, i.e. its physical characteristics. The second is the reflux ratio, i.e. the way in which the column is used.
The principle of fractional distillation requires that the vapours rising up the column encounter the condensed liquid running down the column. If, in the extreme case, all the vapour rising up the column were drawn off at the top via the collection valve there would be no liquid left for flowing back down the column. So there would be no counter-current flow and no separation. At the other extreme, if the collection valve were closed and all the condensed liquid flowed back down the column (total reflux) the separation would be excellent but no product would be obtained. Obviously there has to be a compromise and this is achieved at a reflux ratio of about 10:1.
This ratio refers to the volume of liquid flowing down the column at total reflux compared to the volume drawn off through the collection valve. Thus, if the heat input to the boiler were causing the liquid to reflux at a rate of 1000 ml per hour, 100 ml per hour of distillate could be drawn off as usable product. The balance of 900 ml per hour would be flowing back down the column to provide the multiple mini-distillations required for the separation. It will be appreciated that the 10:1 ratio is not critical ... 8:1 would be acceptable and 12:1 even more so. The 10:1 figure is simply a reasonable value which is known to give good results.
So the first step involved in determining just how much alcohol can be produced per minute or per hour is to find out the rate of reflux in the fractionating column, i.e. the boil-up rate. When we have this figure we divide by ten and this is the volume of 95% alcohol which can be drawn off through the collection valve in the still-head.
The way to proceed is as follows: With a known wattage input establish steady refluxing conditions and then open the collection valve WIDE. Measure the output per minute, either in terms of volume using a graduated cylinder or by weight using a sensitive scale. You may wish to repeat with other wattage inputs.
We found that with 750 watts input to the boiler the rate of reflux was 45 ml per minute. Other wattage inputs gave proportional volumes. This means that with 750 watts input and a reflux ratio of 10:1 we can draw off 4.5 ml of 95% ethanol per minute. In practice we use about 4 ml to be on the safe side.
With slight variations in the construction of your column, in the way you have packed it, and the amount of insulation you have used, you'll probably get slightly different results from the above, so do measure the rate of reflux for yourself. It's simple and informative.
It is not very convenient to set the collection valve each time you carry out a distillation by using the volume which flows out in one minute. It is too cumbersome. A better method is to laboriously find a valve-setting which does deliver 4 ml per minute and then count drops using a stopwatch. Thus, 4 ml per minute might represent, say, 30 drops in 10 seconds. Knowing this you can quickly adjust the collection valve to the right setting by counting drops with a stopwatch.
Collect at least 250 ml of this first distillate and put to one side for future processing and then start to collect the pure alcohol in a clean receiver. Throughout this early phase test the distillate with your nose to see if you can detect any trace of heads.
The 250 ml or so of early distillate which have been put aside may be perfectly pure but the nose and the palate are extremely sensitive organs, particularly the palate, and you would quickly detect an off-flavour if it got through into your final drink. Play it safe, therefore, and put aside a generous portion of the initial distillate, even as much as 500 ml. It will not be wasted because, in a few weeks time, when a number of distillations have been completed and several litres of doubtful distillate accumulated, it can all be redistilled and really pure alcohol recovered from it.
When all the ethyl alcohol has distilled over, which may take as long as 20 hours, the temperature will start to rise as the higher boiling point "tails" appear. Experience will tell you when to expect this to happen and you should start switching receivers well ahead of this point so that only a small volume of alcohol will be contaminated. The last receiver containing a trace of tails can be added to the discard bottle for later purification.
When the fractional distillation is complete the packing in the column will be flooded with tails. These should be thoroughly washed from the column by pouring generous quantities of hot water down from the top.
When carrying out a fractional distillation for the first time the rate of production of pure alcohol will seem to be extremely slow. At a few drops per second one can believe that it will take forever to produce a reasonable amount and there will be a tendency to open the collection valve a little wider to increase the flow. Resist this temptation and be patient. The apparatus requires no attention and it is surprising how much alcohol is produced at a flow rate of 2 or 3 drops per second for several hours. Thus, at 750 watts input to the boiler and a draw-off rate of 270 ml. per hour, over 3 litres of pure, 95% alcohol will be obtained in a 12 hour day. This, when diluted with water and flavoured, will provide over 7/ litres of gin.
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