PRODUCTION
The raw materials
required for the production of Malt Whisky are barley, water and
yeast. The production process can be broken down into five stages.
MALTING
MASHING
FERMENTATION
DISTILLATION
MATURATION
MALTING Back
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First the barley is MALTED, that is the barley is germinated to
convert the starches in each grain into a simple sugar. Distillers
look for plump, ripe barley with plenty of starch and not too
much nitrogen.
Barley is
a food cereal similar to wheat and oats. It has always been the
primary raw material for conversion to malt. The preference for
barley over other cereals is undoubtedly the fact that the corn
or seed is covered with a straw-like husk that is not removed
by threshing and protects the grain during the process stages
in malting. The husk subsequently serves as a filter in the mashing
operations.
The origin
of the barley is not important. Although Scottish barley is considered
to be the most suitable, due to the soil and climatic conditions,
there is not enough to satisfy the industry demand. Barley is
imported from England and other countries. Originally the barley
was grown locally and malted at the distillery, as evidenced by
the familiar pagoda-shaped roofs of the malt kilns visible at
some whisky distilleries. Today only a handful of distilleries
have their own maltings; these include Highland Park, Glenfiddich,
Bowmore, Laphroaig and Springbank. Specialist maltsters can provide
distillers with more consistent malt made to their detailed specifications.
A grain of
barley consists of two main parts, the Embryo and the Endosperm.
The embryo is the important part of the corn, all the organs which
will develop into a future plant being present there in a modified
form. The Endosperm is the chief food storage organ of the seed
from which the Embryo draws its food supplies in the early stages
of germination. Also present in the corn, both in the Embryo and
the Endosperm (to a limited extent) are substances known as proteins.
Also secreted in the barley are Enzymes, which develop during
germination and, in association with other Enzymes formed in the
process, degrade the starch hydrolytically to provide simple fermentable
sugars.
The object
of malting is, therefore, to develop Enzymes and in particular
Diastase of Malt and to modify or make friable the starch contained
in the grain. This is carried out in three stages, steeping, germinating
and kilning or drying. These processes must be affected in such
a manner as to provide maximum fermentable matter (Malt Extract),
adequate Diastatic Power and ensure minimum malting loss due to
respiration etc.
STEEPING
The steeping cycle in the steep tanks is variable according to
the quality of the barley and is, of course, dependent on the
time taken for the moisture content of the barley to rise to the
desired level. Generally a 60-hour cycle is adequate. During this
period the water will have been changed at least three times,
air rests, the number and lengths of periods having been first
determined, will have taken place and regular periods of aeration
of the steep water will also have been carried out.
GERMINATION
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Until recent years, floor malting was operated in the conversion
of barley to malt. The disadvantage of this system is the difficulty
of removing or counteracting the influence exerted on the malting
process by atmospheric conditions. A large amount of space is
necessary and the cost of employing the essential skilled workers
is high.
Today floor
malting is practically non-existent and the germination process
is usually carried out in pneumatic maltings either Box Maltings
or Drum Maltings.Box
Maltings are generally more common and the essential feature is
that temperature controlled air, saturated with moisture to a
humidity of 100%, is passed through the bed of germinating grain
contained in a concrete box and via perforations in the box floor.
This system provides ideal conditions for the germination of the
barley to proceed irrespective of the atmospheric conditions.
The germination period is reduced in comparison with floor malting,
production increased and a considerable economy affected in labor.
Turners are
provided in the germinating box to ensure that all the grain contained
therein is kept free, leveled and receive similar treatment in
the passage of air throughout the bed. Having sprouted, the barley
is now termed "green malt" and is ready for drying.
KILNING OR
DRYING Back to Top
Germination having been completed the grain or "green malt" as
it is now termed is transferred by screw and elevator to the Malt
Kiln for drying. In Kilning, perfect control as far as is possible,
should be established over the temperature of drying and economy
in the use of Fuel. The Kiln is a tower shaped structure with
a furnace provided at the base. The hot air chamber is located
above the furnace.It distributes the heat from the furnace evenly
under the wedge wire floor on to which the grain has been spread.
The wedge wire floor is so constructed as to allow an easy passage
for the hot air to pass through the grain. The upward draught
of hot air may be natural but is often assisted by a powered fan.
The furnace
is a simple grate in which coke or anthracite and peat is burned.
The drying of the grain performs the following functions.
Peat is
formed from decomposed vegetable matter and the peat "reek" or
smoke given off from combustion is imparted to the Malt. In the
early drying stages whilst the grain is in a soft moist condition
the peat "reek" permeates into the corns. In the latter drying
stages the outer skin of the seeds will also be flavored.
Finally,
on termination of the Kilning the Malt is removed to be stored
in Bins for five to six weeks. This period of time is necessary
to allow the heat to be dissipated naturally. The use of hot Malt
is not conducive to the satisfactory function of one of the later
functions, i.e., Fermentation.
In preparation
for the next stage, Mashing, the malted barley must first be ground
and this is carried out on a four-roller mill. Magnets are installed
in the Mill to prevent pieces of metal passing through and making
contact with the revolving rolls. Such an occurrence could cause
a spark within the mill and create a fire and/or explosion.
The quality
and consistency of the ground malt or Grist is all important if
maximum extraction of fermentable matter is to be obtained in
the Mashing operation. An ideal Grist should have as many of the
husks as is possible, unbroken in appearance, although they should
have been split open to release the starch. Unbroken husks provide
a more buoyant Mash and give better filtration in the Mash-Tun
by allowing the liquor to percolate through. Husks that have been
crushed into numerous small pieces are liable, due to liquid pressure,
to pack and thus impair drainage in and from the Mash-Tun.
In so far
as the starch is concerned it is the aim of the Millman to break
it down into minute gritty particles without creating flour. Some
flour is unavoidable but this should be kept to a minimum. Fine
grits allow the water to mix readily but flour resists mixing.
If too much flour has been produced it creates bad filtration
and often "soggy" or "sticking" mashes giving bad drainage. A
visual examination of the grist provides an experienced operator
with a good idea of the quality.
To obtain
maximum efficiency, however, it is essential to know the exact
quality of the grind. For this purpose a hand screening box which,
when shaken, can separate a sample into three portions is used.
Ideal Grist should have the following components.
- Coarse
Materials and Husks 14% by weight
- Fine Grits
78% by weight
- Flour
8% by weight
Barley seeds
and consequently Malt corns vary in size and it is therefore necessary
to close or open the Mill Rolls to ensure that a Grist of the
quality described is obtained. This entails regular sampling and
checking by the Millman in order to obtain a Grist, which will
provide the maximum Mash Tun Extract of fermentable matter.
MASHING
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The object
of Mashing is to render soluble and to dissolve as much of the
valuable contents of the Malt as is possible. This produces a
sweet liquid or sugar solution termed Wort containing in addition
to the sugars intermediate products.
The materials
used in the Mashing process are Water and ground Malted Barley.
The quality of the water plays an important part throughout this
process and finally in the quality of the spirit produced. All
waters tend to differ to some extent in the quantity and type
of minerals and organisms contained therein. Generally speaking,
hard waters are considered unsuitable and soft waters are preferred.
An ideal process water would be one rising from a whinstone or
granite strata, acid in nature and flowing through peaty soil
with a minimum of metal content.
Springs and
burns should be protected, wherever possible, to prevent contamination
and water tanks and pipes should be scoured and sterilized frequently.
It is undesirable to use water that has lain in tanks and pipes
for some time. Such water may well contain bacterial and dissolved
metals. In short, poor quality water should never be used in the
process and regular analyses can assist in this respect.
The only
cereal in the production of Malt Spirit is malted barley. Malt,
as stated, contains a high percentage of starch together with
enzymes that possess the power to convert starch to sugar when
mixed or mashed with water. Enzymic action is influenced to a
large extent by temperature, Ph and concentration of the mash.
The ground
malt or Grist is conveyed to a hopper or bin situated above the
Mash-Tun and mashing can commence. The Mash-Tun is a circular
metal vessel provided with mechanical stirrers that revolve and
rotate to thoroughly mix the Mash of Grist and Water as necessary.
A perforated false bottom, to allow the liquor to drain through
and discharge to a holding tank termed a Worts Receiver, covers
the whole surface of the bottom of the Mash-Tun. Whilst the liquor
drains off through the perforations the grains are retained in
the Mash-Tun. The process involves the application of three waters.
First
Water
Hot water at a temperature of 156ºF and the Grist are brought
together simultaneously in a Mashing Machine, situated above and
discharging into the Mash-Tun. The mixing of the Grist and the
Water combines to give a striking temperature of 148ºF - 149ºF.
When the Mash-Tun has been filled to the required capacity the
temperature of the mass should be 147ºF - 148ºF. At this temperature
the desired conversion proceeds rapidly. Great care must be exercised
in regulating mashing temperatures, as variations will seriously
affect the fermentability of the liquor. The Mash is allowed to
sit for 1 hour to ensure maximum conversion at this temperature.
The Wort
is, thereafter, drained into the Wort's receiver, cooled through
a Heat Exchanger and pumped to the fermenting vessels called Wash
Backs. It is necessary to cool the Wort as Yeast, which is added
to the sugar solution, will not live or propagate in high temperatures.
The Wort is therefore cooled to 72ºF at which temperature fermentation
is rapidly incited by the action of the Yeast. In cooling the
Wort in the Heat Exchanger the cooling agent is, of course, water
and the heat from the Wort is transferred to same resulting in
warm water at a temperature of 125ºF being returned to the Brewing
Tanks for further use. This practice effects a saving in steam
and consequently an economy in the use of coal.
Second
Water
All the First Water liquor having been drained from the Mash-Tun
a second Water is added to the bulk of the grains left in the
Mash-Tun. No more Grist is added and the Second Water is applied
at 172ºF giving a temperature of the mixture in the Mash-Tun of
157/159ºF. Quantitively the Second Water is usually about half
that used for the First Water. The temperature is raised to further
assist extraction and render soluble ant starch particles which
had not been dissolved at the lower temperature of the First Water.
The Mash, when the Second Water has been added, is again left
"sitting" for a period of thirty minutes for conversion to take
place. The liquor is thereafter drained, cooled and passed to
the Wash Back.
Third
Water
The
grains left in the Mash-Tun still contain a small percentage of
sugars. This is too valuable to lose and accordingly a Third Water
raised to a temperature of 190ºF - 195ºF is applied. The stirrers,
in this instance, are used vigorously to ensure thorough mixing
and complete the final extraction. The liquor from the Third Water,
which is a very weak sugar solution, is termed Sparge. It is returned
to the Brewing Tanks to be used as the mashing liquor of the First
Water of the next Mash. These operations should, therefore, obtain
maximum extraction and minimum loss. The grains left in the Mash-Tun
are, after the Third Water liquor has been drained off, removed
mechanically and sold to Dairy Farmers. A high milk yield is forthcoming
from the use of these grains known as Draff.
FERMENTATION
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YEAST
Yeast is a unicellular microorganism, that is to say, it is a
living organism whose individual units are visible only under
the microscope. It belongs to the planet kingdom and is classified
as one of the fungi. There are many different species of yeast
but the one normally encountered in the distilling and brewing
industries is called Saccharomyces Cerevisiae. To give some ideas
of the minute size of this micro-organism, three fully grown yeast
cells placed end to end will measure only one thousandth part
of an inch and in a 1 lb packet of yeast, there are approximately
seven billion cells. (7,000,000,000,000).
REPRODUCTION
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VEGETATIVE: - The usual way in which yeast reproduces itself is
by "budding" i.e. asexual means of propagation. A small protuberance
first appears on the cell wall and gradually grows until a new
cell is formed. This new cell can have a daughter cell of its
own and so on. With ideal growth conditions one yeast cell can
produce thirty yeast cells in three days.
SPORULATION: - this is also an asexual means of propagation which
is very much more rare. When a yeast cell finds itself in a position
where growth conditions are adverse, for example, when there is
little or no food available, it forms spores. Within each cell
four spores are formed and these eventually rupture the cell wall
and escape into the surrounding liquid. Some of these spores are
male and some female and when conditions are once again favorable
and food is available pairs of spores unite to form new yeast
cells.
ACTION OF
YEAST IN WORT Back to Top
When yeast is introduced into a sugar solution such as Wort there
are three ways in which it utilizes the sugar.
- For multiplication
i.e. it uses sugar to form new cell material.
- Fermentation:
- This is an anaerobic reaction in that it occurs in the absence
of air.
- Respiration:-
This is an aerobic reaction and occurs if a constant source
of oxygen is available.
The action
of the yeast when added to the Wort can be divided into three
phases.
(1) The lag phase where there is little fermentation. The yeast
is busy adapting itself to its new surroundings and this is the
period when contaminating bacteria can cause a great deal of damage.
(2) The log phase being the period of rapid fermentation when
there is a rapid rise in temperature and fermentation is so vigorous
that "switchers", rotating metal blades, must be employed to keep
down the frothy head.
(3) Phase of restricted growth where the fermentation slows down
and eventually terminates.
Yeast (1%
by volume) is added as soon as possible to the cooled Wort being
pumped into the Wash Back. This is done in the very early stages
in order to quickly establish fermentation. It is more readily
accomplished by providing the yeast with the ideal nutrient, the
strong high gravity Wort of the initial liquor from the First
Water. A strict control is kept on the Wort temperature and maintained
until all the Wort from both the first and second waters has been
collected in the Wash Backs. When all the Wort has been collected
in the Wash Back the final temperature should be around 72ºF.
however, if the sugar concentration of the Wort is likely to be
high and a very quick acting yeast has been used, the collection
or setting temperature should be dropped two or three degrees.
A rise in
temperature takes place during fermentation from 72ºF - 94ºF.
If the temperature exceeds the last figure and the temperature
rise has been excessively rapid, this can destroy the yeast resulting
in a poor fermentation and loss of spirit. Great care must therefore
be exercised in the setting temperature and due allowance made
for any abnormalities such as high concentration of sugars in
the Wort.
The rate
of fermentation is variable and is dependent on many factors such
as the type of yeast, quantity, its condition, the setting temperature,
the temperature in the Fermenter Room, the type of malt, the available
Diastase, suspended solids in the Wort, mashing temperatures,
purity of water and so on. Sometimes fermentation will appear
to be continuing after fifty hours. Generally fermentation after
forty-eight hours is negligible.
The cause
of poor fermentation can be attributed to a number of factors,
some of which are given below.
(1) The
use of Malt low in Diastasic Power.
(2) Bacterial infected yeast.
(3) Excessively high percentage of dead cells in yeast.
(4) Incorrect mashing temperatures.
(5) Bacterial infection in vessels, pipes, pumps, valves etc.
It is of
paramount importance that all vessels in the mashing and fermentation
processes be kept 100% clean and free from bacteria. To this end
a very strict cleaning and sterilization of all plant is adhered
to and no relaxation of the cleaning operations is permissible.
Bacterial infection can have a serious effect on the yield of
spirit and also adversely affect the quality of the spirit.
DISTILLATION
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Distilling
takes place in pairs of copper pot stills with tall 'swan-necks'.
One is usually larger than the other, otherwise their shapes,
heights and sizes vary from distillery to distillery. The life
of a still is between 15 and 30 years, depending on how hard it
is used.
The two main
operations in distilling are turning liquid into vapor and then
vapor into liquid i.e. vaporization and then condensation. Distillation
is simply a means of separation by these operations. A liquid
can be separated from solids or one liquid from another and either
the distillate or the residue collected.
The wash
is pumped into the larger of the two stills, called the 'wash
still', where it is brought to the boil. Stills are either heated
directly from below (by gas, oil or coal) or from within by steam
heated coils, not unlike those found in electric kettles.
The Wash
contains solids such as dead yeast etc. from the fermentation
process and it is necessary to keep these solids in suspension
during the distillation period. This is done by means of a "rummager"
inside the still. The "rummager" consists of three rotating arms
to which are affixed webs of copper chain and also brass links.
The webs scour the bottom and flue plates of the Still. This prevents
the adherence of solids and thereby prevents the Still from being
burnt.
The temperature
has to be carefully controlled to prevent the foaming wash from
rising up the swan-neck and into the condenser. A small window
in the neck tells the distiller how far the wash has risen.
The alcoholic
vapors and steam rise over the neck and into the condenser - essentially
a series of pipes in a cold-water jacket. Here the vapors return
to liquid at about 21 per cent alcohol and are termed low wines.
The Low Wines,
thereafter, flow through the Spirit Safe, which is the control
point of distilling operations, to a vessel called the Low Wines
& Feints receiver. Inside the Spirit Safe, fabricated of brass
or copper and glass and kept securely locked by the Customs &
Excise, samples of the running distillate may be drawn and the
strength tested by means of a hydrometer located inside the Safe.
They then
pass through into the second still, the 'low wines still' or 'spirit
still'. The same process is repeated in the second distillation,
but this time the distiller watches the spirit carefully as it
passes through the spirit safe. The early part of the run (known
as 'foreshots') is pungent and impure. He test the spirit by adding
water (which turns it cloudy), measuring its specific gravity
and watching the clock, and until the foreshots run clear, he
directs it back to the low wines and feints charger to be redistilled.
This takes between 15 and 45 minutes depending on the size of
the still.
When he is
sure that the run is clear, the stillman redirects the spout and
begins to collect the spirit for maturing. This is 'new make',
and will run between two and fours hours, depending on the size
of the still, commencing at about 70 to 75 percent alcohol and
decreasing steadily down to between 60 to 65 percent.
The precise
strengths, the speed at which he operates his still and the length
of time he saves spirit (known as the 'cut') is part of his art
and influences the flavor and quality of the product. It varies
from distillery to distillery but the 'new make' may be about
one third of the spirit distilled. Only part of the run is collected,
because about halfway through the second distillation, various
oily compounds called 'feints' begin to vaporize. They are mild
and pleasant at first, lending character and flavor to the whisky,
but in time their intensity increases to such a degree that to
continue to collect the spirit will spoil the whole batch.
The stillman
will again direct the distillate to the low wines and feints charger
for re-distillation. Distilling continues until all that is left
is 'spent lees' (more or less water). The distillation of 1,500
gallons (6,800 liters) of low wines and feints normally takes
about six hours.
MATURATION
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In this discourse
up to this point no mention has been made of whisky. This is simply
because the spirit produced cannot legally be termed Scotch Whisky
until it has been matured in oak casks for at least three years.
If it is
intended to sell the Malt Spirit as a single Malt Whisky then
at least eight years maturation or preferably ten to twelve years
will be necessitated.
No reputable
distiller would market Malt Whisky or even Blended Whisky at such
an immature age as three years. The maturation of whisky i.e.
the change from a raw harsh spirit to the smooth, mellow aromatic
whisky, so acceptable to most, is to a great extent a closed book.
It is known, of course, that the spirit vaporizes and permeates
through the cask into the atmosphere and that moisture from the
atmosphere is drawn into and mixed with the spirit in the cask.
It is also known that, proportionally, the congenerics change
in relation to their original content in new spirit. This is,
of course, due to the variance in vaporization tendencies.
Many millions
of gallons of spirit are lost due to the vaporization during maturation.
In the past efforts have been made to artificially mature whisky.
These efforts, one is glad to state, have proved unsuccessful.
Electrolysis, the use of Catalysts and other methods have all
been tried but not with any real degree of success. It is to be
hoped that no artificial process of quick maturation will be forthcoming
and thus ensure that, although more and more chemistry is being
applied to the production of Scotch Whisky, it will still remain
an art and not a science.
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