The Production Process - Distillation
Distillation refers to a process of utilizing differences in boiling point temperatures to separate alcohol from water, in other words, to concentrate alcohol and flavors.
Malt whisky is batch distilled in pot stills whereas grain whisky is continuously distilled in column stills. We shall focus on batch distillation in this article.
A pot still is a large, hand-crafted pot with curved sides that are 5-10 millimeters thick. Copper is used because it is easy to shape and is an effective heat conductor. Moreover, copper acts as a catalyst to produce various flavor compounds as well as to eliminate and separate unpleasant flavor compounds by reacting with the sulfuric compounds in alcohol vapor.
Types of Stills
Different sizes and shapes of pot stills will result in different styles of spirits. There are bulge, straight, and lamp-glass-shaped stills. The straight-shaped pot stills produce strong, heavy spirits. The bulge-shaped stills have a ball-shaped structure in the mid section of the still whereas the lamp-glass-shaped stills look very similar to an hourglass; these stills produce lighter flavors than a straight still. But this alone does not determine the character of the spirit. The height of the still, the angle of the lyne arm (the horizontal component on top), the method of heating and even the type of condenser make a difference.
There is direct-fire distillation and indirect steam distillation. The character of the spirits likewise differs greatly depending on the method of heating.
Direct-fire distillation: Heat is applied directly to the bottom of the pot using a gas or coal fire. It is easy to burn the inside bottom of a still so a rotating chain inside the pot is used to prevent burning. Direct-fire distillation is less common these days. This method tends to produce whisky with a strong, toasty character.
Indirect steam distillation: Heat is applied to the wash by running steam through pipes inside the pot. The character of the spirits produced is lighter than that of direct-fire distillation.
The role of the Condenser
The condenser cools the vapor that reaches it through the lyne arm and liquefies it. It too is made of copper. There are 2 types of condensers.
Worm tub: Alcohol vapors are cooled as they pass through a coiled copper tubing inside a water tank.
Shell and tube: With a completely opposite construction to a worm tub, in a shell and tube method, cool water flows through copper tubes, cooling and liquefying vapor as it comes in contact with the surface.
The first distillation extracts flavor compounds from the wash and raises the alcohol content to around 20 percent. Approximately one-third of the wash becomes low wine, the remaining two-thirds is pot ale and draff, which is processed and used to make animal feed and fertilizer.
The low wine is transferred to the spirit still and distilled once more to further concentrate the alcohol and flavor compounds. Distillate from the condenser during the second distillation is divided into three stages in the following order: the heads, the heart and the tails. Only the heart (i.e. the new make spirit) is transferred into casks for maturation. Collecting the heart, which includes the distillates most desirable flavor compounds, is the important part of the second distillation. It will contain approximately 65-70 percent alcohol content. The heads and tails are combined together and with the next batch of low wine to be distilled. These cut points are controlled using a spirit safe.
低度酒轉移到第二個壺式蒸餾器，進行第二次蒸餾，以進一步濃縮酒精和味道。 在二次蒸餾期間，從冷凝器餾出的餾液會按照以下順序分為三個階段：酒頭，酒心和酒尾。 只有酒心（即新製成的原酒）會被引流到木桶中進行陳化。 酒心是二次蒸餾的重心，包含餾出物中最理想的味道，酒精度在 65-70％左右；而酒頭部和酒尾則會混合起來，與下一批低酒度一同進行蒸餾。酒頭，酒心和酒尾的分段位受到烈酒保險箱控制。