Winegrowers Supplies  -  The process for making whisky - Malt whisky and Grain whisky

1. Malting:

Barley (a cereal grain, like wheat or oats) is first spread out in a 30 cm deep layer on a concrete malting floor, it is then sprayed with water.
Warm air is blown over it for several days until it starts to sprout/germinate. It is turned regularly to prevent the build up of excessive heat.
Traditionally, this was done by tossing the barley into the air with wooden shovels in a malt barn adjacent to the kiln.
During this process enzymes are activated which convert the starch into sugar when mashing takes place.

After 6 to 7 days of germination/growth the barley, now called green malt, goes through a kiln which dries it out and stops the growth.
The heat in the kiln is kept below 70C so that the enzymes are not destroyed.
Some of the malt is kilned for longer, become darker in colour, ranging from pale brown to completely black. Darker malts are used to give colour and flavour.

Malted barley is the source of fermentable sugars. Most of the simple sugars extracted from the malt during the fermentation process are transformed by the yeast, producing carbon dioxide and ethyl alcohol. Some more complex sugars remain unfermented and remain as 'residual sugar', which gives the whisky its body and malty sweetness.

Grain whisky is usually made from 10 to 20 % malted barley and then other unmalted cereals such as corn-maize or wheat.
The starch in the non-malted cereals is released by pre-cooking in a Cereal Cooker, which converts it into fermentable sugars.
The mashing and fermentation processes are similar to those used for malt whisky.

2. Milling the grain:

Different types of malted barley (and other grains, for Grain whisky), depending of the recipe, are measured, mixed together and ground into a coarse 'grist' in a special mill.

3. Mashing:

The grist is transferred into the 'Mash Tun' and combined with hot water to form a thick 'porridge', called the mash.
The water is added in 3 stages and usually gets hotter at each stage, starting around 67C and rising to almost boiling point.
This then soaks at 65 C for about 40 to 60 minutes. During this time, the starch in the malt is being broken down and converted into sugars by enzymes in the grain.
The mash is stirred, helping to convert the starches to sugar.

Note: A spray-ball system is fitted in the top of the Mash Tun, to use for sparging, and subsequently for CIP of the Mash Tun.

Next sparging begins: hot water at 75 C is sprayed on the mash. The sweet sugary liquid extract, called wort, is drawn off the bottom of the tank and pumped into a Fermenter.
About two-thirds of the dry weight of the original grist is converted into sugar and ends up in the Fermenter.
The spent grains - the draff - are separated/removed and processed into animal feed.

Note: the hot water required is heated to around 75 C in a Hot Liquer Tank, insulated and conventionally using cheaper 'night rate' electricity.
Alternatively, a stainless steel heat exchanger could be installed inside the HLT, heated by hot water from a diesel fueled boiler, and linked from the Chiller (heat exchanger) which cools the wort after the boil, so that heat extracted from that is used to heat the water in the HLT.

4. Fermentation

The wort is cooled to 20C and pumped through a hose into a Washback (Fermenter or FV), where yeast is added and fermentation begins.
A wort aerator could be installed in the hose inlet to the FV.

The living yeast feeds on the sugars, producing alcohol and small quantities of other compounds, which contribute to the flavour of the whisky.
Carbon dioxide is also produced and the wash froths violently. Revolving switchers cut the head to prevent it overflowing.
After about 2 days the fermentation dies down and the wash contains 6-8% alcohol by volume.

Note: The fermentation vessel (FV), ideally with cooling jacket to slow the fermentation, could be a cylindro-conical shape.
Or the FV can be a normal 'pressureless' tank, with a pressure-relief-valve, to release the CO2 given off in the fermentation.
A spray-ball system is fitted in the top of the FV, to use for CIP.

5. Pot Still - for distillation of Malt whisky:

In some mysterious way the shape of the pot still affects the character of the individual whisky, and each distillery keeps its stills exactly the same over the years.
In distillation, the still is heated to just below the boiling point of water and the alcohol and other compounds vaporise and pass over the neck of the still into either a condenser or a worm - a large copper coil immersed in cold running water where the vapour is condensed into a liquid.

The wash is distilled twice: - first in the wash still, to separate the alcohol from the water, yeast and residue called pot ale. The solids are also saved for use in animal feeds.

- the distillate from the wash still, known as low wines, and containing about 20% alcohol by volume, then goes to the spirit still for the second distillation.
The more volatile compounds which distill off first - the foreshots, and the final runnings called feints where more oily compounds are vaporised, are both channelled off to be redistilled when mixed with the low wines in the next batch.
Only the pure centre cut, or heart of the run, which is about 68% alcohol by volume is collected in the spirit receiver.

6. For Grain whisky, the wash is distilled in a continuous or Coffey still, named after its inventor Aeneas Coffey.

It has two tall columns - a rectifier and an analyser. Cold wash is pumped in at the top of the rectifier and meets steam.
The columns in fact act like a heat exchanger. The alcohol is cooled, condenses and flows away as Scotch grain spirit at about 94% alcohol by volume.

The distilled grain spirit is lighter in character and aroma than most malt whiskies and therefore requires rather less time to mature.
The bulk of matured grain whisky is used for blending.

7. Spirit Safe

All the distillates pass through the spirit safe - whose locks were traditionally controlled by Customs & Excise.
The distiller uses all his experience to test and judge the various distillates without being able to come into physical contact with the spirit.
The newly distilled, colourless, fiery spirit reduced to maturing strength, 63% alcohol by volume, is filled into oak casks which previously may have contained Scotch whisky, bourbon or sherry, and then the maturation process begins.