Russell I. (ed.) Whisky. Technology, Production and Marketing
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148 Whisky: Technology, Production and Marketing
Table 4.7
Comparison of steam and chemical sterilants for washbacks
Method Advantages Disadvantages
Stainless steel:
Steam Already available (for stills, etc.), no
residue
Radiated heat affects nearby
washbacks
Metal fatigue from repeated
expansion and contraction
Cannot remove soil from surfaces
Chemical Suitable preparations remove
organic and inorganic soil
Requires subsequent rinsing with
sterile water
Can be applied at ambient
temperature (although 50–608Cis
preferable)
Wood:
Steam Available, no residue, as above Cannot remove soil from surfaces
Probably unable to sterilize within
crevices or between planks
May eventually damage structure of
wood
Chemical Removal of soil at moderate
temperature, as above
Complete removal of sterilant is
impossible (the necessary rinsing
would be impracticable)
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Introduction
Unlike grain whisky production, malt whisky production is essentially a dou-
ble ba tch-distillation process using pure malt, water and yeast as the raw
materials. In size, the production capacity of a malt distil lery is a tenth the
capacity of a typical grain distillery. This chapter discusses the history of batch
distilling; the design and construction of stills and ancil lary equipment; the
operation of wash and spirit stills; product quality; efficiency (production
yield); and triple distillation. It goes on to consi der how to deal with distilla-
tion problems, describes laboratory techniques employed in batch distillation,
and finally looks to the future.
History
Distillation was carried out from earliest times using pot stills, initially made
of ceramics or glass and eventually of copper (Nicol, 1997). These early stills
were fired by open fires in a furnace or hearth or, if the charge to be distilled
was heat sensitive, by placing the still in a water or sand bath to reduce the
action of direct fire. The distillates were originally condensed using air con-
densers, which resembled tapering lyne arms, to deliver the product to a glass
or clay vessel. The evolution of the worm tub and eventually the shell and tube
condenser revolutionized the cooling of distillates.
Alcohol was not recovered by distillation in any quantity until the twelfth
century, when stills of crude design caulked with clay and straw were
improved upon by using a close-fitting pot, head and lye pipe so that the
recovery of alcohol was facilitated by the distillation of inferior, unpalatable
beers and wines without the alcohol escaping through ill-fitti ng connections.
153
Chapter 5
Batch distillation
Denis Arthur Nicol
Whisky: Technology, Production and Marketing Copyright 2003
ISBN 0-12-669202-5 All rights of reproduction in any form reserved
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The production of alcohol was the preserve of monks in monasteries, within
whose cloisters alchemy was practised in the fruitless search for the
Philosopher’s Stone, wh ich was thought to be central to the transmutation
of base metals into gold. The Elixir of Life was also sought, to no avail; alcohol
filled this niche and apparently was prescribed as a panacea for all ills.
The Reformation saw the dissolution of the monasteries in England and
Scotland. With the dispersion of the monks their knowledge as brewers, dis-
tillers, barber-surg eons, alchemists and apothecaries was released into the
secular, material world. The monks had become the founders of the early
medical sciences, bre wing and distilling industries. Thus whisky (uisge
baugh), first witnessed by Henry II of England (whose army invaded Ireland
in 1170) as being produced from cereals by the natives of that land, had
mention in the Scottish Exch equer Rolls of 1494 as aqua vitae or ‘water of
life’, alluding to that tantalizing and unattainable Elixir of Life.
Design of distillery
All malt whiskies derived from low-nitrogen malted barleys are produced in
copper pot stills (Nicol, 1989) of time-honoured traditional design. (Figure 5.1)
The following principal elements comprise a pot still, whether for distilling
wash or low wines:
. Heating source – direct fire (coal or liquid petroleum gas), or indirect fire (oil,
steam coils, kettles or pans)
. Pot – contains charge to be distilled
. Shoulder
. Swan neck
. Head
. Lyne arm, lye pipe or vapour pipe
. Worm tub or condenser
. Tail pipe
. Spirit safe.
Figure 5.2 shows the overall layout of a typical malt distillery.
Heating source
As noted above, there are several fuels available for the distiller to heat the
stills (Watson, 1989). With direct-fired stills, the pot must be designed to
withstand the rigour s of the direct firing and the copper crown and flue
plates must be made of a sufficient gauge of copper to withstand the intense
local heating. Where the copper is not exposed to such intense heat, its gauge
can be less. The base of the direct-fired still is convex, resembling an inverted
saucer. The hearth or furn ace upon which the still rests is of brick or steel
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Chapter 5 Batch distillation 155
Figure 5.1
Pot still design. 1, pot; 2, steam heating coil; 3, crown; 4, flue plate; 5, shoulder; 6, ogee;
7, swan neck; 8, head; 9, lyne arm/lye pipe; 10, vapour chamber; 11, shell and tube
condenser; 12, water jacket; 13, tube bundle; 14, tail pipe with siphon; 15, charging line/
valve; 16, air valve; 17, anti-collapse valve; 18, discharge line/valve/sight glass; 19, steam
line/valve; 20, cradle.
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156 Whisky: Technology, Production and Marketing
Figure 5.2
Typical malt distillery layout. 1, washback; 2, wash charger; 3, wash preheater; 4, wash
still; 5, wash still condenser; 6, wash condenser; 7, wash still safe; 8, low wines receiver/
charger; 9, low wines/spirit still; 10, low wines/spirit still condenser; 11, spirit still safe;
12, intermediate spirit receiver (ISR).
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construction, lined with suitable firebricks to protect the supporting structure
from the heat.
Whether gas- or coal-fired, the exhaust gases must be ducted to a flue stack
or chimney made of brick or steel. Wi th more than one still the flue gas can be
led into a manifold, the flue gas flow being individually controlled by dam-
pers. Where coal is used as the heating medium, each hearth is equipped with
a chain grate stoker with automatic solid-fuel feed and ash removal. A damper
is fitted to the flue to control the heat input. With gas firing, the burner can be
modulated by controlling the gas flow.
For indirect heating by coil, pan or kettle, steam is supplied by an oil- or gas -
fired boiler and is transferred by a steam main from the central boiler at the
crown pressure; this pressure is reduced to the desired operating pressure for
the internal heating elements. The heating elements must be designed to be
totally immersed in the relevant charge to be distilled, at the beginning and
end of the distillation cycle. A low wines and spirit still can be fitted with an
extra coil that can be used distil the middle cut gently, ensuring good reflux.
Steam traps are strategically positioned to remove any condensate that may
waterlog the steam lines; condensate returns, post-heating, are fed to the boi-
ler-feed water tank as an energy-saving step via a condensate manifold. The
steam demand is calculated to provide sufficient energy to bring a still into the
safe within an hour or less. The calculation should include the maxim um
demand for steam when heating hot liquor tanks and distilling several stills
simultaneously. The boiler output is then designed on this demand and sized
accordingly, with extra capacity includ ed.
Direct firing of wash stills requires a rummager, a geared shaft from which a
flail made of copper or brass is suspended. This rotates, scouring the flue plate
and base of the wash still and preventing the build-up of char red material that
would otherwise adversely affect the heat transfer.
To conserve energy, the external flue plates of an indirectly fired still can be
insulated to prevent radiant heat losses through the sides of the pot. The
shoulder and all other parts of the still should not be insulated as this
would adversely affect the reflux, which is essential for spirit character –
especially in the spirit still.
Wash preheating, when used, can considerably shorten distillation times
and thus save energy. A treatise on energy-sav ing techniques can be found
in Whisky Distilling (1985).**20
Pot
The pot (Figure 5.3) can assume many shapes (Whitby, 1992) – conical, onion,
cylindro-conical, inverted cone, ball and lantern – provided that sufficient
volume and surface area is maintained to ensure that the coils remain totally
immersed at the end of the distillation. This is not a problem for directly fired
stills.
The pot is equipped with close locking air, charging, discharging and safety
valves. If manually operated, a special interlocking valve key that is shared
Chapter 5 Batch distillation 157
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between the air, discharge and charging valves is used. It can only be used in
sequence, ensuring that the air valve followed by the discharge valve can be
opened to prevent collapse or accidental discharge of the still. The reverse is
applicable on charging, with sequential closing of the discharge valve, fol-
lowed by the opening of the charging valve and finally closure of the air
valve on the completion of charging and the application of heat.
Such requirements are redundant with today’s use of automatic remote
control through programmable logic controllers (PLC) with sequencing opera-
tions.
The pot connects to the swan neck via the ogee. Access to the pot is provided
by a lockable brass man door.
158 Whisky: Technology, Production and Marketing
Figure 5.3
Still design configuration. 1, onion – lyne arm descending; 2, plain – lyne arm ascending;
3, straight – lyne arm horizontal; 4, ball – lyne arm descending; 5, lantern – lyne arm
descending/horizontal; 6, ball – lyne arm horizon tal/ascending.
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Swan neck
The design of the neck can vary from short to long; it can be slightly tapered,
straight-sided or severely swept in to the head. At the base of the neck it can be
designed to resemble a lantern glass, assume a ball-shape or be connected
directly to the pot with the still resembling an onion. The neck is usually
provided with two sight glasses situated on opposite sides of the neck so
that any foaming up the still, especially from boiling wash, can be observed.
A light can be attached to the rear sight glass to illuminate the still internally.
A cold finger can also be instal led at the top of the neck. This is supplied
with cooling water, which is used to prevent any foam from boiling over into
the receiver. To complete the attachments to the neck, a vacuum relief safety
valve is fitted well above the reach of any foaming distillate in a wash still to
avoid seizure of the valve seat by solids.
Head
The head is a curved extension of the neck, connecting it to the lyne arm or lye
pipe. The head can be fitted with a thermo meter to indicate the imminent
arrival of condensate. The length or height of the head will dictate the degree
of reflux within the still.
Lyne arm
The lyne arm, lye pipe or vapour pipe is of cylindrical construction and con-
nects the head to the worm or shell and tube condenser.
The attitude of the lyne arm has an important bearing on the spirit char-
acteristics. It can be designed to be horizontal, ascending, or descending to the
condenser or worm tub, and may be short or long. Such permutations as there
are will affect the nature of the new spirit.
The lyne arm can be interrupted by a purifier – a device fitted with baffles
and cooled by an external water jacket or an internal coil. It is used to encou-
rage heavy oils (higher fatty acid esters) to return to the still during distilla-
tion. The purifier returns the oils to the shoulder of the pot via a U-bend.
Worm tub or condenser
The worm tub is a vessel that contains a long coiled tube tapering to a nominal
76 mm at its outlet. The tub in which the worm is held is supplied with cooling
water, which enters at the base of the tub and overflows at the top. At certain
times of the year (in late spring or early summer) the supply of water may be
insufficient to provide adequate cooling, and in such circumstances it may be
necessary to incorporate a cooling tower or plate heat exchanger into the cool-
ing circuit, the condenser water being air or water cooled. Seawater can be
used for cooling heat exchangers in coastal distilleries.
Chapter 5 Batch distillation 159