This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
Coming to more recent times, there are excise records from the year 1827 onwards, which show that in Scotland, in the years 1827.9, when pot-stills alone were used, the quantity of spirits made from mixed malt and grain was only a little less than the quantity made from malt only. But it became much less in subsequent years, so far as the pot-stills were concerned. A small quantity of sugar and molasses was also employed, about the middle of the last century; but since then, with the exception of one year (1887), the Scotch pot-still distilleries appear to have used only malt, or malt and grain, the quantity made from malt only being always largely in excess of that made from the mixture of malt and unmalted grain. In recent years. wherever the pot.still process has been exclusively employed, malt only has been used, . and practically no materials other than malt and unmalted grain have been used in either pot. or patent.stills.
A large majority of the Irish pot-stills have always produced spirit from a mixed mash of malt and unmalted grain. The quantity made by them from malt only has always been small in comparison. No other materials than malt and unmalted grain have been used to any great extent in the Irish pot-stills, or indeed in the patent. stills, during the last fifty years.
The unmalted grain employed in making whisky includes barley, maize, oats, rye, and wheat. For the manufacture of pot-still whisky in Scotland, barley malt is generally the only material employed in the mash; but in the Irish pot-still distilleries, with few exceptions a mixture of barley-malt and unmalted barley, oats, wheat, and rye is employed, maize being generally excluded. The proportions vary, with the view of obtaining particular flavours in the resulting whisky; but it may be taken that generally four. fifths of the whole mash consists of barley, malted and unmalted, and that the remaining one-fifth is made up of oats, wheat, and rye, in proportions decreasing in the order of enumeration.
For the patent-still process, the materials employed in the mash are much the same in both Scotland and Ireland. They are selected from malt, maize, barley, rye (malted and unmalted), and oats. The precise proportions in which they are used vary in different distilleries with the object which the distiller has in view. Thus in one Scotch distillery the mash was made up of 25 per cent. malt, 72 per cent. maize, and 3 per cent. oats; in another of 30 per cent. malt, 30 per cent. rye, and 40 per cent. maize. In one Irish distillery, it consisted of 35 per cent. malt and 65 per cent. of a mixture of barley and maize; in another, malted barley, rye, and maize were used in the proportions of 28, 36, and 36 per cent., respectively. Maize is very extensively used, both in Scotland and Ireland, in the patent-still process. Malted rye is also used in the mash in some patent-still distilleries, it being considered to improve the "body" of the whisky.
The general operations of distillation have already been described in Chapter II (Outline Of The Production Of Alcohol), but some further points bearing more especially upon the production of whisky may be mentioned here, or recapitulated. The simplest varieties of the pot.still are to be met with in Scotland, having long necks, but not otherwise furnished with any special means to secure rectification of the spirit. Other pot-stills, however, are in frequent use which are provided with pipes or circular vessels fitted between the neck of the still and the condenser, thus increasing the power of rectification. Such stills are, in effect, intermediate between the simple pot-still and the patent-still. As regards mode of heating, some are heated by direct fire, others by steam pipes and steam jackets. It is held by some distillers that this difference of heating is important in respect of the character of the whisky produced, in that the open fire causes a charring of the wash, and thus adds empyreumatic bodies to those already present. Others, however, contend that no difference is to be detected in the whisky obtained, whether steam or direct fire be employed.
In Scotland, two distillations are commonly required for preparing pot-still whisky from the wash. The first takes place in the "wash. still," all the alcohol being collected in one distillate, technically termed 'low wines," together with secondary constituents and some water. The low wines are redistilled from a smaller still, and collected in three fractions, (1) "foreshots," (2) the clean or finished whisky, and (3) "feints." The foreshots and feints are collected together and redistilled with the next charge of low wines.
The judgment and experience of the distiller determine the point at which the collection of foreshots is stopped, and that of whisky commenced; and, similarly, that at which the latter is stopped and the collection of feints begun. The strength at which the whisky fraction is run is generally about 11° to 25° over proof.
Fig. 44. - pot.still for direct firing. With retort, rectifier, wash heater and condenser (Blair, Campbell & McLean, Glasgow).
In some Scotch distilleries, however, the whisky is produced in three distillations; the spirit is then run off at 40° to 45° over proof. This practice is very general in the Lowlands.
Three distillations appear to be universally practised in Ireland for obtaining pot-still whisky; and the method of collecting fractions is somewhat more complicated than with the Scotch process. Strong low wines and weak low wines, strong feints and weak feints, are collected, and probably different practices obtain in every Irish distillery. The whisky fraction is usually run at a higher strength than in the Scotch practice, namely, from 25° to 50° over proof.