There are two kinds of Scotch Whisky: Malt Whisky
which is made by the Pot Still process and Grain
Whisky which is made by the Patent Still (or Coffey
Still) process. Malt Whisky is made from malted
barley only, while Grain Whisky is made from malted
barley together with unmalted barley and other cereals.
The Pot Still process by which Malt Whisky is made
may be divided into four main stages:
Malting, Mashing, Fermentation and Distillation.
- (a) Malting
The barley is first screened to remove
any foreign matter and then soaked for two or three
days in tanks of water known as steeps. After this it
is spread out on a concrete floor known as the
malting floor and allowed to germinate. Germination
may take from 8 to 12 days depending on the
season of the year, the quality of the barley used and
other factors. During germination the barley secretes
the enzyme diastase which makes the starch in the
barley soluble, thus preparing it for conversion into
sugar. Throughout this period the barley must be
turned at regular intervals to control the temperature
and rate of germination.
At the appropriate moment germination is stopped
by drying the malted barley or green malt in the malt
kiln. More usually nowadays malting is carried out in
Saladin boxes or in drum maltings. in both of which
the process is controlled mechanically. Instead of
germinating on the distillery floor, the grain is
contained in large rectangular boxes (Saladin) or in
large cylindrical drums. Temperature is controlled by
blowing air at selected temperatures upwards
through the germinating grain, which is turned
mechanically. A recent development caused by the
rapid expansion of the Scotch Whisky Industry is for
distilleries to obtain their malt from centralised
maltings which supply a number of distilleries,
thereby enabling the malting process to be carried
out more economically.
- (b) Mashing
The dried malt is ground in a mill
and the grist, as it is now called. is mixed with hot
water in a large circular vessel called a mash tun.
The soluble starch is thus converted into a sugary
liquid known as wort. This is drawn off from the
mash tun and the solids remaining are removed for
use as cattle food.
- (c) Fermentation
After cooling, the wort is passed
into large vessels holding anything from 9,000 to
45,000 litres of liquid where it is fermented by the
addition of yeast. The living yeast attacks the sugar in
the wort and converts it into crude alcohol.
Fermentation takes about 48 hours and produces a
liquid known as wash, containing alcohol of low
strength, some unfermentable matter and certain
by-products of fermentation.
- (d) Distillation
Malt Whisky is distilled twice in
large copper Pot Stills. The liquid wash is heated to a
point at which the alcohol becomes vapour. This
rises up the still and is passed into the cooling plant
where it is condensed into liquid state. The cooling
plant may take the form of a coiled copper tube or
worm that is kept in continuously running cold water,
or it may be another type of condenser.
The first distillation separates the alcohol from the
fermented liquid and eliminates the residue of the
yeast and unfermentable matter. This distillate,
known as low wines, is then passed into another still
where it is distilled a second time. The first runnings
from this second distillation are not considered
potable and it is only when the spirit reaches an
acceptable standard that it is collected in the Spirit
Receiver. Again, towards the end of the distillation.
the spirit begins to fall off in strength and quality. It is
then no longer collected as spirit but drawn off and
kept, together with the first running, for redistillation
with the next low wines.
Pot Still distillation is a batch process.
The Patent Still process by which Grain
Whisky is made is continuous in operation and differs
from the Pot Still process in four other ways.
- The mash consists of a proportion of malted
barley together with unmalted cereals.
- Any unmalted cereals used are cooked under
steam pressure in Converters for about 3'/2 hours.
During this time the mixture of grain and water is
agitated by stirrers inside the cooker.
- The starch cells in the grain burst and
when this liquid is transferred to the mash tun, with
the malted barley, the diastase in the latter converts the
starch into sugar.
- The wort is collected at a specific
gravity lower than in the case of the Pot Still
- Distillation is carried out in a Patent or Coffey
Still and the spirit collected at a much higher strength .
Both Malt and Grain Whisky must be
matured after distillation has been completed. The new
spirit is filled into casks of oak wood which,
being permeable. allows air to pass m and evaporation
takes place. By this means the harsher constituents in
the new spirit are removed and it becomes in due course
a mellow whisky. Malt Whisky which contains more of
these flavoury constituents takes longer to mature than
Grain Whisky and is often left in the cask for 15 years
or even longer.
The period of maturation for both Malt and Grain
Whisky is also affected by the size of casks used. the
strength at which the spirit is stored and the
temperature and humidity of the warehouse.
After maturation the different whiskies are
blended together. (See Question 20 for a description of
the blending process). The blend is then reduced to the
strength required by the addition of soft water. The
different whiskies in the blend will have derived some
colour from the casks in which they have been
matured, but the degree of colour will vary from one
whisky to another. Whisky matured in former fresh oak
sherry casks will usually be a darker colour than that
which has been matured in refilled whisky casks. The
blender aims at uniformity in his product and he may
bring his whisky to a definite standard colour by adding,
if necessary, a small amount of colouring solution
prepared from caramelised sugar, which is
infinitesimal in relation to the volume of whisky
involved. The whisky is then filtered carefully.
The final stage in production of Scotch
Whisky is packaging and despatch. Most Scotch Whiskies
are marketed at home and abroad in branded bottles.
In some instances for commercial reasons Scotch
Whisky may be shipped overseas in bulk. When blended
Scotch Whisky is shipped abroad in bulk, either at
original strength or suitably reduced it is exported in
glass lined stainless steel tanks or casks of varying size
according to the market. The bottling is then carried out
by distributors or agents overseas.
© SWA 1995