|Wash still (bladnoch.co.uk)|
|Dalwhinnie||Glen Spey||Springbank (wash) |
Basically the first distillation is a simple distillation of volatile compounds (such as alcohols), producing low wines of 20-25% abv from 6-9% abv wort. Wash is usually preheated to prevent excessive temperature differences and charring inside the still. The first distillation is usually deemed complete when the distillate is under 1% abv and about one third of the wort has boiled over to the wash safe. Wash distillation usually takes 5-8 hours to complete, depending on the size, shape, temperature and charge of the still. The residual is called pot ale.
The wash distillation is mixed with the foreshots and the feints from previous spirit distillations and distilled in the spirit still. The second distillation is a fractionated distillation; the most volatile compounds boil first and are called foreshots or heads, the second part is called the middle cut (spirit cut, heart), the third part is feints (tails) and the remaining liquid in the still is called spent lees.
|Boiling point C||Odor|
|acetone||56,5||nail polish remover|
|acetaldehyde||20,2||pungent fruity, green apple, metallic|
|amyl alcohols||102-138,5||sharp, burning|
|2-phenyl ethanol||219||floral, rose|
|ethyl formate||54||rum, raspberry|
|hydrogen suphide||-60,3||rotten eggs|
|sulphur dioxide||-10||burnt sulphur|
|dimethyl sulphide||37||cabbage, vegetables|
|lauric acid||299||bay oil, soap|
|palmitic acid||351||waxy, creamy, soapy|
The traditional way of making the first cut point is by mixing the foreshots with water in the spirit safe; as the spirit turns clear, the foreshots have mostly passed and the middle cut is collected into the spirit receiver. Some producers use timed foreshot runs and do not bother with the demisting test and therefore are are likely to cut the spirit a bit lower as a precaution and probably getting less of the highly volatile compounds into the spirit. The second cut can be determined by taste, abv or time according to the distillery practice. The feints are then run usually down to 1% abv and added to the next wash.
The feints are the last volatile fraction of spirit distillation. Feinty aromas increase slowly towards the end of distillation, developing from quite pleasant mushroom, cereal and popcorn aromas to leathery tobacco notes and further to ashy, fishy and even cheesy aromas not usually approved in whisky. The feints are usually rich in phenols and smoky aromas important for peaty whiskies. Therefore the second cut point must be determined with care to produce peated but not feinty spirit with off-notes. The feints are usually run quite fast to save time, but this makes some of the fat-solubles to adhere to the still. These compounds (mostly fatty acids) must be purged by an adequately long and slow run of foreshots in the next distillation, otherwise the whisky might become feinty no matter how early the second cut is made.
The spirit cut is usually about 72-65%, but there are considerable differences between distillers. To produce a very light aetheral whisky (richer in high volatiles) the distiller would be likely to use a tall still with a low charge run slowly in low temperatures for maximum reflux, a purifier, an ascending lyne arm, a purifier and a shell&tube condenser for maximum copper contact and cut short foreshots and long feints (earlier second cut) for maximum amount of high volatiles and less of the heavier aromas. To produce a peaty whisky the distiller must try to catch all the phenols from the latter part of the middle cut but also avoid excess feints.
The distillation is not only a simple process of separation, but the heat and the copper contact alter some of the flavour compounds, too. Heat promotes Maillard reactions producing furfural and sulphur compounds, especially thiophenes and polysulphides, which at low concentrations add a pleasant roasted and complex flavour, but produce pungent and unpleasant cereal and sulphury notes at high concentrations. Heat also promotes aldehyde reduction to alcohols and acids and their conversion further to esters. Lignin-derived components such as coumaric and ferulic acids can evolve to more spicy guiaicols. Acrolein (peppery) can form from bacterial fermentation products in presence heat. Fusel oils, 2-phenethanol (rose, flower) and furfurals (caramel, burnt sugar) are formed in pot-stills, but not significantly in column still distillations and therefore are likely to be generated by heat differences during distillation.
Copper removes most of the sulphury, cereal, feinty and meaty aromas during distillation. Especially the copper contact of the first wash still distillation is important. Total removal of copper contact in the spirit still has surprisingly minimal effect on the mentioned off-notes.
References and further reading:
Adams AB. The distillation of alcohol. J Ind Eng Chem 1912; 8-14
Herstein KM. Chemistry and technology of wines and liquors. Van Nostrand Co 1935
Jounela-Eriksson P. The aroma composition of distilled beverages and preceived aroma of whisky. Academic Press 1978
Lea GH, Piggott JR. Fermented beverage production 2nd ed. Kluwer Acad 2003.
Monica Lee KY et al. Origins of flavour in whiskies and a revised flavour wheel. J Inst Brew 2001;107;5;287-313
Piggott JR, Paterson A (ed). Understanding natural flavors. Blackie academic&professional 1994
Russell I (ed). Whisky, technology, production and marketing. Academic Press 2003
Udo M: The Scottish Whisky Distilleries. Black & White 2006
Walker GM, Hughes PS (ed). Distilled spirits, new horizons: energy, environment and enlightenment. Nottingham Univ Press, 2010
Webb AD (ed). Chemistry of winemaking. Am Chem Soc 1974