In reality there is quite some distance between the two first thresholds and very little between the last. This means that if one only raises the heat a little to move the thresholds up a bit one can drive out the top 6-7 thresholds and get weaker impure spirits. This illustrates the importance of keeping the temperature accurate. If the temperature is held the thresholds are kept in place. That is why it stops dripping from a correctly calculated and accurately adjusted Lab Master still when the alcohol nears exhaustion.
We transfer the crystal clear mash to the boiling vessel using a syphon without disturbing the lees. The boiling vessel must not be filled right up, allow at least 200 mm for boiling. The mash expands when it is heated and spare volume for this is necessary.
The distilling apparatus should be assembled and the cooling water connected up. The cooling water only needs to run slowly. After 13 hours (depending on mash volume and boiling plate capacity) the distillation starts. The first 4 centilitres should be thrown down the drain as they are comprised of by-products (including aldehydes) which are formed during fermentation. These can most accurately be described as scent-like substances and have a boiling point of about 65°C. They are entirely harmless and can be retained, but the flavour will be improved if they are not included.
Now set the temperature at the column head. This is done by roughly setting the heat source and a fine adjustment of the cooling water. A perfect distillation takes place 1-2 tenths of a degree centigrade under boiling point of alcohol. Try to set 78°C. It is imperative that the temperature is under 80°C.
After 8-12 hours distillation (or other period of time) it is time to finish the process. Exactly when will be seen by the temperature at the column head. Either the temperature rises, so one switches off at 90°C. The temperature can also drop 10-20°C or more and the spirit stops dripping from the apparatus. This is because one has succeeded in setting the temperature so accurately and with the alcohol all gone from the mash the water cannot get through the
column. From a batch of 22-25 litres of mash, one should be able to produce 2-2 3/4 litres of 90-95%, concentrated alcohol. In practice this means 4-6 litres of 40-45% spirit. Sometimes more with the use of Turbo yeast.
Undo the connector between the column and the boiling vessel and set aside the apparatus to cool. Air must be allowed into the vessel, otherwise the resultant vacuum can cause the boiling vessel to implode.
When the mash has cooled pour it out into the lavatory. Rinse out the vessel and reverse rinse the column. Use a detergent when washing the boiling vessel, column and column filling.
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