Distillation A Malt Whisky

The production of malt whisky involves batch-distillation of the fermented liquid in two copper pot stills, namely the wash still and the spirit still (Fig. 3).

The contents of the fermentation vat are transferred to a large wash still, of capacity 15,000 to 30,000 liters, and boiled for 5-6 hr to produce a distillate (the low wines) that contains 20-25% ethanol (35-45° proof British). The low wines are distilled in the spirit still to produce the following three fractions:

1. Foreshots

2. Whisky (potable spirit containing 63-71% ethanol: 120-150° proof British)

3. Feints (approximately 25% ethanol).

The distillate is run through a spirit safe, prior to maturation, in order to determine the quality of the spirit. The ethanol content is determined by hydrometry because ethanol possesses a specific gravity lower than that of water.

The careful selection of the cut points during this distillation procedure greatly influences the flavor of the final product. The first cut from foreshots to spirit governs the level of aldehydes and short-chain esters; the second cut (spirit to feints) determines the concentrations of higher alcohols and acids. The foreshots and feints are returned to

Distillation Cut Points

Condensate to boiler

Figure 3 Pot still for batch distillation in the production of malt whiskey. (From Ref. 5.)

Condensate to boiler

Figure 3 Pot still for batch distillation in the production of malt whiskey. (From Ref. 5.)

the process, being redistilled in the spirit still with the next batch of low wines. The conditions of distillation also enable further reactions to occur with respect to whisky flavor development:

1. Continuing ester formation

2. Maillard reaction and the accompanying Strecker degradation to produce aldehydes (especially acetaldehyde, 2-furaldehyde, 5-hydroxymethyl-2-furalde-hyde)

3. Continuing formation of volatile sulfur-containing compounds from corresponding nonvolatile precursors

4. The conversion of h-hydroxypropionaldehyde to acrolein:

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