Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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economical point of view. The value of 90% is con-

sidered the practical limit of salt removal due to

decreasing electrical conductivity with demineraliza-

tion. ED is likely to have advantages for plants with

high hourly utilization rates, for the manufacture of

products that do not require high levels of demineral-

ization, and where low-cost electricity is available.

Based strictly on economics, the recent trend is to-

wards combined ED ion exchange plants. The major-

ity of ED plants use preconcentrated sweet whey as

well as acid whey, skimmed milk, delactosed whey,

milk, whey protein concentrate, and whey ultrafiltra-

tion (UF) permeates.

0009 Whey produced by ED has a reduced mineral con-

tent and is rich in lactose and whey proteins, and

contains appropriate low levels of essential minerals,

which makes it an ideal ingredient for infant formu-

las. Raw whey is concentrated to 23–27% solids, and

clarified before ED. Liquid or dried reduced-minerals

whey could be used for blending infant formulas, but

a high level of demineralization (90%) is required for

sweet whey to be used in an infant formula. The use

of reduced-minerals whey as an ingredient in infant

formulas must be ranked as one of the major suc-

cesses in terms of the valuable and profitable use of

a byproduct. Reduced-minerals whey could be used

in animal feeds, protein and citrus drinks, dry mixes,

confectionery coatings, icecream, and bakery goods.

0010 Although the trend has been towards the use of

whey protein-based infant formulas, there is also a

considerable percentage of infant formulas produced

in which nonfat milk is used as the sole source or

protein. These products tend to have higher ash con-

tents, including higher levels of phosphorus, calcium,

sodium, potassium, and chloride, than whey protein-

based formulas. Other ED applications include the

partial demineralization of whey protein concentrate,

which is ideal for products that require a higher pro-

tein-to-lactose ratio; acid whey for mixing with sweet

whey in the manufacture of whole whey powder; and

of cottage cheese whey in order to reduce disposal

problems.

0011 ED is also used in various integrated membrane

systems for specific purposes, e.g.:

0012 Nanofiltration/ED systems: nanofiltration is used

to concentrate and partially demineralize whey

prior to ED, which in turn completes demineral-

ization to the desired level.

0013 UF/ED systems: UF allows molecules, such as

sugars and salts, to pass through the membrane

while protein molecules are retained. UF is used

to produce whey protein concentrate (WPC) while

ED demineralizes the WPC to produce a low-ash,

high-protein ingredient for infant formulas.

Microbial Fermentation Systems

0014Membrane techniques are well established in

fermentation processes and are increasingly used in

integrated bioprocesses. Figures 2 and 3 give an indi-

cation of the possible implementation of an inte-

grated bioprocess in the dairy industry using cheese

whey/waste water as substrate for the production of

lactic acid. Regarding the fermentation of concen-

trated substrates, one application for the ED tech-

nique during upstream processing may be a partial

reduction of the salt content and to obtain osmotic

pressure to their optimum values. A final microfiltra-

tion step can be incorporated to obtain a continuous

Dairy waste water

Cells

Lactic acid

Purified waste water

Whey protein

Integrated

bioprocess

fig0002Figure 2 The recovery of lactic acid and other products of value

from whey/dairy waste water, using an integrated bioprocess

system. Courtesy of Fraunhofer Institute for Interfacial Engineer-

ing and Biotechnology, Stuttgart, Germany.

Whey

Cells

Microfiltration

Ultrafiltration

Retentate

Permeate

Medium

preparation

Additives

CSTR CR

−

CFBR

Bioreactor

Precleaned

waste water

Neutralization agent

Lactic acid

Bipolar electrodialysis

fig0003Figure 3 An integrated bioprocess for the production of lactic

acid from whey using an integration of membrane systems in

combination with a fermentation process. CSTR CR, continuous

stirred tank reactor with cell recycling; CFBR, continuous fluid-

ized-bed reactor. Courtesy of Fraunhofer Institute for Interfacial

Engineering and Biotechnology, Stuttgart, Germany.

WHEY AND WHEY POWDERS/Applications of Dialysis 6169

delivery of sterile substrate to the bioreactor. In con-

tinuous fermentation systems, membranes can be

used for cell separation, retention of metabolic com-

pounds, and recirculation. The reaction compounds

are discharged from the membrane reactor with the

permeate, which is then replaced by a new substrate

solution. Owing to cell retention, cell density and,

hence, substrate conversion velocity can be signifi-

cantly enhanced.

0015 The application of ED in downstream processing

offers many economically competitive methods for

the recovery of whey-based lactic acid:

0016 Continuous cell recycling with UF or microfiltra-

tion membranes followed by the removal of lactic

acid by ED units.

0017 Acid recovery by means of ED with bipolar mem-

branes (Figures 3 and 4). Bipolar membranes con-

sist of cation and anion exchange layers arranged in

parallel between two electrodes which enable the

lactate salt to be split and electrically neutralized by

ions and the corresponding alkali. The function

of the bipolar membrane in the electrodialytic pro-

duction of acids and bases from the corresponding

salt solution is based on its capability for enhanced

water dissociation under the influence of an electric

potential gradient.

The combination of technologies and the demand for

specialized products will in future lead to the next

generation of highly differentiated whey protein-

based products, with specific functionalities.

Other Applications of Dialysis

001 8 Dialysis and ED techniques are also applied in the

demineralization of foods such as soy sauce, fruit

juice, vinegar, hydrolyzed vegetable protein, sugars,

and wine; deacidification of foods; purification of

fermented products, hydrolysates, lipopolysacchar-

ides, and protein fractions; as well as for the isolation

of flavor substances and the production of enzymes.

Other applications include the recovery of salts,

acids, or alkali from industrial rinse waters as well

as the purification of drinking water supplies, e.g.,

drinking water nitrate reduction.

Seealso: Cheeses:ChemistryofGelFormation;

ManufactureofExtra-hardCheeses;ManufactureofHard

andSemi-hardVarietiesofCheese; Effluents from Food

Processing:MicrobiologyofTreatmentProcesses;

DisposalofWasteWater; Infant Foods:MilkFormulas;

WeaningFoods; Membrane Techniques:Principlesof

ReverseOsmosis;ApplicationsofReverseOsmosis;

PrinciplesofUltrafiltration;ApplicationsofUltrafiltration;

Whey and Whey Powders:ProductionandUses;Protein

ConcentratesandFractions;FermentationofWhey;

PrinciplesofDialysis

Further Reading

Batchelder BT (1987) Electrodialysis applications in whey

processing. In: Trends in Whey Utilization. IDF Bulletin

no. 212, pp. 84–90. Brussels: International Dairy Feder-

ation.

Bylund G (1995) The chemistry of milk. In: Dairy Process-

ing Handbook, p. 17. Lund, Sweden: Tetra Pak (Process-

ing System Division).

Bylund G (1995) Whey processing. In: Dairy Processing

Handbook, pp. 331–351. Lund, Sweden: Tetra Pak (Pro-

cessing System Division).

Fraunhofer Institut Grenzfla

chen- und Bioverfahrenstech-

nik (2001) Integrated bioprocesses – recovery of value

products from waste materials. Internet: http://

www.igb.fhg.de/UWbio/en/Lactic_acid.en.html. Ac-

cessed 6 November 2001.

Horton B (1998) The whey processing industry – into the

21st century. In: Whey, special issue 9804, pp. 12–

25.Brussels: International Dairy Federation.

Ionics (2001) Membrane systems for food and dairy

processing. Internet: http://www.ionics.com/products/

WaterFoodChemical/FoodProcessing/fooddairy.htm.

Accessed 12 January 2001.

Kulozik U (1992) Membranes in microbial fermentations.

In: New Applications of Membrane Processes. Special

issue 9201, pp. 141–160. Brussels: International Dairy

Federation.

pez-Leiva MH (1988) The use of electrodialysis in

food processing. Part 2: Review of practical applica-

tions. Lebens-mittel-Wissenschaft und Technologie 21:

177–182.

Mostert JF and Roberts JJ (1993) Applications of dialysis.

In: Macrae R, Robinson RK and Sadler MJ (eds)

Encyclopaedia of Food Science, Food Technology and

Nutrition, vol. 8, pp. 4905–4908. London: Academic

Press.

From the fermenter

Bipolar membrane

−

Lac NH

−

Lac

HLac

−

Further

purification

To the

fermenter

−

fig0004 Figure 4 Schematic diagram of the function of bipolar electro-

dialysis membrane. Reproduced from Kulozik U (1992) mem-

branes in microbial fermentations. In: New Applications of

Membrane Processes. Special issue 9201, pp. 141–160. Brussels:

International Dairy Federation, with permission.

6170 WHEY AND WHEY POWDERS/Applications of Dialysis

WHISKY, WHISKEY, AND BOURBON

Contents

Products and Manufacture

Composition and Analysis of Whisky

Products and Manufacture

J R Piggott, University of Strathclyde, Glasgow, UK

J M Conner, The Scotch Whisky Research Institute,

Riccarton, Edinburgh, UK

Synopsis

0001 Whiskies are distilled beverages which have been

produced by the distillation of fermented cereals and

have been matured in oak casks. They can be classi-

fied according to starting material, blending and

country of origin. The major grains used in whisky

production are maize, barley, wheat and rye. Amylase

activity required for starch breakdown is obtained

from malted barley, and some regulations permit the

use of other enzymes. The yeast used for fermentation

of the cereal extract is normally a specially developed

strain of Saccharomyces cerevisiae. Distillation is in

small pot stills or continuous column stills, followed

by maturation normally for at least 3 years in oak

casks.

Types of Product

0002 Whiskies are distilled beverages that have been pro-

duced by the distillation of fermented cereals and

have been matured in oak casks. They can be classi-

fied on the basis of the nature of the cereal, the

manner in which the product is blended, if at all,

and the country of origin. Although there is some

evidence for a distillation-type process in ancient

Egypt, the first reports of whisky production arise in

Ireland in the twelfth century, and the first description

of a whisky production process is found in Scottish

records dating from 1494. The term ‘whisky’ is

derived from the Gaelic ‘uisge beathe,’ which means

‘water of life.’ Major countries of production are

Scotland, the USA, Ireland, Canada, and Japan,

while similar products are produced in many other

countries including Brazil, Korea, and Spain.

0003 Regulations in the European Union (EU) define

whisky as a spirit produced by the distillation of a

mash of cereals and matured for at least 3 years in

wooden casks. There are limitations on the enzymes

that can be used to hydrolyze starch to fermentable

sugars and on the distillation strength, and yeast must

be used for the fermentation. Within this definition,

Scotch and Irish whiskies are further restricted. In

practice, this provides for three distinct products:

malt whisky, produced from 100% malted barley;

grain whisky, produced from unmalted cereal grains;

and the bulk of the whisky produced in Scotland,

which is blended from 60–70% grain whisky and

30–40% malt whiskies. This blended whisky usually

contains up to 40 individual malts that are blended to

produce a consistent brand flavor, and every compon-

ent of the blend must be matured for the minimum

period, or the age specified on the bottle. Malt

whiskies may contain either a blend of malt whiskies

of a given minimum age or malt whisky from a single

distillery. Scottish malts have a different character

depending upon whether they are from the west

coast, such as Campbeltown and the Islay region,

which produce highly peated malts, or from the High-

lands or the Lowlands. Irish whiskies have a similar

flavor to Scotch but do not have a peaty character.

0004Whisky produced in the USA has evolved in a

different legislative framework, allowing for a greater

variety of distinctive products. The basic definition of

US whiskey is that it is distilled from a fermented

grain mash at less than 95% alcohol (190



proof). Within this broad definition, there are two

special categories, which are bottled as such or

provide flavoring whiskies for blending. In the first

group, the cereal content of the mash is restricted to

not less than 51% of the named cereal (e.g., rye for

rye whiskey, maize for Bourbon), the distillation must

be at less than 80% alcohol, and maturation must be

in new charred oak. Bourbon takes its name from

Bourbon County in Kentucky. Corn whiskey must

be from a mash of 80% maize, and matured in new

uncharred or used oak. If matured for 2 or more

years, these are ‘straight whiskies.’ They are to the

blender the equivalent of the Scotch malts, and pro-

vide the majority of the flavor in a blend with lighter

flavored grain spirits. US blenders are also permitted

to use ‘blending materials,’ such as sherry or blending

wine, at up to 2.5%. (See Barrels: Wines, Spirits, and

WHISKY, WHISKEY, AND BOURBON/Products and Manufacture 6171

Other Beverages; Sherry: The Product and its Manu-

facture; Wines: Production of Table Wines.)

0005 Canadian whisky production follows the same gen-

eral practice as in Scotland and the USA. Canadian

blends are light column still whiskies with normally

10–15% of heavier-bodied flavoring whiskies. Up to

9.09% (on the basis of absolute alcohol content) of

‘flavorings’ is permitted, which may include wines

and sherries, rum, brandy, bourbon, or malt whisky.

Maturation must be for not less than 3 years, and oak

casks of 182 l (40 imperial gallons) are commonly

used. The range in flavor required by the blender

cannot be achieved by using the products of many

different distilleries, but techniques such as variation

of the composition of the mash (corn, wheat, rye or

barley), cooking procedures, yeast strain, distillation

procedure, barrel type, and maturation period can be

used. Traditionally, pot stills were used but these have

largely been phased out. (See Brandy and Cognac:

Armagnac, Brandy, and Cognac and their Manufac-

ture; Rum.)

0006 Similar products are produced in many other coun-

tries and are subject to local regulations, which, while

generally similar in principle to the EU definition,

allow different extents of variation. In Brazil, regula-

tions permit the addition of a proportion of agricul-

tural alcohol to blended whisky, and in Japan, the

locally produced spirit is frequently blended with

imported Scottish malts. Spain is a substantial produ-

cer of whisky, which must meet the EU requirements.

EU and USA regulations also include provision for

grain spirits or grain brandies, which are essentially

similar to whiskies but not matured. In other parts of

Europe (e.g., Poland), ‘whiskies’ are produced that

are essentially vodkas, matured briefly and flavored

with wood extracts or other materials, and which

may or may not meet regulations commonly accepted

for whiskies.

Raw Materials

0007 The major grains used in whisky production are

maize (Zea mays), barley (Hordeum polysticum),

wheat (Triticum vulgare), and rye (Secale monta-

num). These are the grains traditionally used for

whisky, on the basis of a high fermentable starch

content providing a good yield of alcohol. A typical

composition of these grains is shown in Table 1.

In Scotland and Ireland, all the amylase activity re-

quired for starch breakdown is obtained from malted

barley, in the form of either a kilned malt, which is

stored at a moisture content of 5%, or a green malt,

which is prepared specifically on site as a source of

enzyme activity for production of grain whisky. Some

regulations also permit the use of other (normally

microbial) enzymes during wort production. Culti-

vars are normally selected on the basis of extract

and fermentability, corresponding to spirit yield, or

enzyme activity in the case of malt for grain distilling.

Enzyme activity should be considered under process

conditions, as this will not be the same as activity

measured under optimum laboratory conditions.

Ethyl carbamate is an undesirable trace component

in distilled beverages, and its content in malt whisky

is largely determined by the cyanogenic precursor,

epi-heterodendrin, in malt. Barley cultivars that do

not contain the precursor are being developed. (See

Barley; Rye; Wheat: Grain Structure of Wheat and

Wheat-based Products.)

0008Water is required for mashing, cooling during dis-

tillation, dilution of the spirit before maturation, and

blending. The quality of the product may be influ-

enced by the nature of the water supplied, and many

distilleries take their water supply from individual

water courses or special wells. Soft water is normally

used for malt distilleries, but some degree of hardness

is preferred in grain distilleries since this has a stabil-

izing effect on the amylase enzymes. The water should

be monitored for chemical and microbiological

contamination and be free of decaying vegetable

matter. The water used for dilution of the spirit must

have a low calcium and iron content, and is normally

demineralized, to minimize the risk of discoloration

or precipitation occurring in the final product.

0009The yeast used for fermentation is normally a spe-

cially grown distilling yeast that has good physio-

logical and microbiological properties for producing

alcohol. However, some recycled brewer’s yeast is

commonly used in Scotland, and yeasts from previous

distillery fermentations may be used in some Bourbon

tbl0001Table 1 Composition of cereals used in the production of

whisky worts

Corn Rye Barley Wheat

Percentage of total

Endosperm 82 87 84 85

Germ 12 3 3 3

Bran 6 10 13 12

Chemical composition (%, dry-weight basis)

Nitrogen-free extract 69.2 70.9 66.6 69.9

Starch 72 68 63–65 69

Sugars 2.6 0 2–3 0

Protein 8 12.6 12 13.2

Soluble nitrogen (% of total) 4.7 0 11 0

Crude fiber 2 2.4 5.4 2.6

Fat 3.9 1.7 1.9 1.9

Ash 1.2 1.1 2 1.9

From Bronsky AJ and Schumann RW (1989) Cereals for whisky production.

In: Piggott JR, Sharpe R and Duncan REB (eds) The Science and Technology

of Whiskies, pp. 1–18. Harlow, UK: Longman Scientific and Technical, with

permission.

6172 WHISKY, WHISKEY, AND BOURBON/Products and Manufacture

processes, which may influence the range of flavor

products in the wash. The main criterion for yeast

strain selection is normally efficiency in converting

fermentable sugars to ethanol. To a limited extent,

strains may be selected to provide the required com-

position and flavor characteristics in the distillate,

particularly the ester content, and yeast cultivation

and storage conditions also affect its performance.

Yeasts expressing glucoamylase activity have been

developed.

0010 Barrels used in whisky production are produced

from either American white oak, Quercus alba and

related species, or the Spanish oak, Quercus robur.

Scotch whisky is traditionally matured in barrels

which have previously been used for Bourbon matur-

ation or sherry production. Spanish sherry produc-

tion is carried out in barrels constructed from either

Spanish or American white oak. Except where the

regulations provide otherwise, barrels are commonly

reused until they fail to provide a satisfactory matur-

ation. Such barrels may be regenerated by scraping

out the inner surface and charring the inside of the

barrel, but this does not produce performance equiva-

lent to a new barrel. During periods when sherry

casks have been in short supply, barrels have also

been wine treated or wine seasoned (filled with sherry

for up to 6 months), and Madeira or port casks are

also occasionally used. (See Barrels: Beer Making;

Sherry: The Product and its Manufacture.)

Method of Manufacture

Malting and Mashing

0011 The traditional method of production involves the

production of wort from cereal grains using amylases

from barley. These a- and b-amylases are produced by

the barley during the malting process. Malting of

barley is carried out by steeping the grain in water

for 2–3 days and permitting the grain to germinate

until the root is approximately one-third the length of

the grain. When this stage is reached, the grain is

dried down to a moisture level of 5% by kilning.

The grain is then stored until immediately prior to

use, when it is milled before being transferred to a

mash tun. In Scotch whisky production, peated malt

is prepared by drying the malt in the presence of

smoke from a peat fire and is an important source

of flavor compounds, normally assessed on the

basis of the total phenols content of the malt (up to

50 p.p.m.), although other components may contrib-

ute to flavor. The nitrosamine contamination of malt

has recently been of concern in Scotch whisky, arising

from the use of natural gas in directly fired kilns. This

can be controlled by the use of burners designed to

reduce nitrogen oxides, by burning sulfur to add

sulfur dioxide to the air stream, or by indirect firing.

(See Flavor (Flavour) Compounds: Structures and

Characteristics; Phenolic Compounds.)

0012Most of the breakdown of the starch occurs during

the process of mashing, which is carried out in a mash

tun. Barley grist can be mashed directly since it has a

high amylase activity, whereas worts produced from

maize and other cereals require the addition of malted

barley as a source of enzymes. The process of mashing

may be a simple batch process similar to the infusion

mashing techniques used in brewing beer, in which

the grist is mixed with water at 63–68



C for 0.5–

1.5 h before the wort is filtered off. However, in the

production of grain whisky, an initial cooking stage,

to gelatinize the starch of the nonbarley cereals, is

required. The cooking may be carried out as a batch

process at 120



C for 1.5 h or, as is more usual in

North America, as a continuous process. In either

case, the mash is cooled to 60–65



C before the add-

ition of the malted barley. Careful control is required

at this stage to prevent the solidification of the gelat-

inized starch. When a cooking stage is used, amylase

activity is normally provided by adding 10–15%

freshly malted barley (green malt) after the cooking

stage (Figure 1). (See Starch: Structure, Properties,

and Determination.)

0013During the malting stage, b-glucanase enzymes are

also produced; these facilitate the breakdown of the

endosperm cell walls and the release of starch and

proteases. The latter are involved in the breakdown of

some of the barley grain proteins to amino acids and

peptides. These amino acids are an essential nitrogen

source for the growth of the yeast. (See Amino Acids:

Properties and Occurrence; Peptides.)

0014The mash is usually filtered prior to the fermenta-

tion to give a clear wort, but in some processes, a

higher yield is obtained by fermenting the whole mash

directly. The composition of a typical Scotch grain

whisky wort is shown in Table 2. Refer to individual

ingredients.

Fermentation

0015The wort, which is produced when the contents of the

mash tun has been filtered, is then transferred to a

fermentation vessel and fermented using one or more

strains of the yeast Saccharomyces cerevisiae to give

a wash containing approximately 7% ethanol and a

large number of flavor compounds. When the wort is

not boiled (as is the case in malt whisky production),

it contains microorganisms and active amylases. It is

cooled to 20–25



C before inoculation with a strain of

distilling yeast and, in some processes, secondary

yeasts. Yeast growth occurs rapidly and is completed

in the first 8–12 h. Ethanol production follows

WHISKY, WHISKEY, AND BOURBON/Products and Manufacture 6173

growth initially, then continues in a linear manner

until the metabolizable sugars have been consumed.

During the growth period, wort sugars are rapidly

metabolized, and the temperature may rise to 33



if it is not controlled. The pH drops from an initial

value of 5.0–5.5 to 4.2–4.5 as a result of the produc-

tion of organic acids, such as acetate, succinate, and

pyruvate. A wide range of flavor compounds, such as

higher alcohols, fatty acids, esters, and carbonyl com-

pounds, are also produced throughout the fermenta-

tion; they pass through into the distillate and

constitute an important part of the product. In con-

trast, glycerol, which is also produced, is nonvolatile

and does not pass into the distillate; this represents an

important loss of yield. At the end of the fermenta-

tion, usually between 48 and 72 h, death and auto-

lysis of the yeast may occur. The fermentation is not a

sterile process, so bacterial contamination can occur.

Most of the bacteria that are introduced from the raw

materials die during the early stages of the fermenta-

tion. However, lactobacilli can survive and grow with

a concurrent formation of lactic acid during the later

stages of the fermentation. There is some suggestion

that limited growth of lactic acid bacteria is beneficial

in flavor terms, but to prevent excessive growth and

resulting yield losses, fermentation is normally com-

pleted in 40–48 h, rather than the longer times trad-

itionally used. Heavy contamination by lactic acid

bacteria can also result in a loss of yield and the pro-

duction of acrid off-flavors. (See Lactic Acid Bacteria.)

Distillation

0016The fermented wash is then distilled either in a series

of two or three pot stills (Figure 2), or in a series of

column stills. The distillation process varies with the

type of product and the country of origin. Historic-

ally, the first whisky processes used copper pot stills,

and this type of process is still used for the production

of malt whisky in Scotland, where two stills – the

wash still and the spirit still – are used. In Ireland, a

three-still process was typical. Pot stills have also

been used in the USA and Canada, but grain spirit

is normally produced by continuous distillation in

column stills. Again, the first continuous process is

associated with Scotch whisky production and the

development of the Coffey or Patent still by Aeneas

Coffey in 1830. The ethanol concentration of the

tbl0002 Table 2 Chemical composition of a typical Scotch grain wort

Content

Total soluble carbohydrate (as glucose) (%) 9.00

Insoluble solids (%) 2.20

Sugars (%)

Fructose 0.13

Glucose 0.29

Sucrose 0.28

Maltose 4.65

Maltotriose 0.96

Maltotetraose 0.15

Dextrin 2.54

Amino nitrogen (as leucine) (%) 0.09

Ash (%) 0.27

Containing P

0.09

Containing K

O 0.09

Containing MgO 0.02

Vitamins (mgml

1

)

Thiamin 0.46

Pyridoxine 0.61

Biotin 0.01

Inositol 236

Nicotinic acid 11.1

Pantothenate 0.71

From Pyke M (1965) Manufacture of Scotch grain whisky. Journal of the

Institute of Brewing 71: 209, with permission.

Scale Scale

Whole-

corn

storage

Ground-

corn

storage

Corn-

slurry

tank

Steam

Hammer mill

Cooking tubes

Water

Enzyme

Scale

malt

Flash

cooler

Vaccum

cooler

To fermenter

Mash cooler

Conversion tubes

Vapor

To condenser

fig0001 Figure 1 Maize process for whisky. From Simpson AC (1985) Advances in the spirits industry. In: Birch GG and Lindley MG (eds)

Alcoholic Beverages. London: Elsevier Applied Science, pp. 51–67, with permission.

6174 WHISKY, WHISKEY, AND BOURBON/Products and Manufacture

distillate determines the extent of impurities (con-

geners) present, a higher strength distillate being

purer aqueous ethanol, and thus its strength of flavor.

0017 In batch distillation processes, all the contents of

the fermenter are transferred to the large wash still

and boiled for 5–6 h to produce a distillate, low

wines, which contains 20–25% (v/v) ethanol. This is

transferred to the smaller low wines or spirit still

where it is distilled to give a spirit containing around

70% (v/v) ethanol (Figure 3). The Coffey still consists

of two columns, referred to as the ‘analyzer’ or ‘beer

column’, and the ‘rectifier column.’ The wash is fed

towards the top of the first column, and alcohol-free

stillage is withdrawn at the bottom of the column;

vapors are fed from the top to the base of the rectify-

ing column (Figure 4). This produces a 190



US Proof

spirit and is still used for the production of grain spirit

in Scotland. In the USA, whisky production employs

more complex distillation processes involving the use

of up to five columns. The heat for most distillation

processes is supplied as steam at the present time,

although pot stills directly fired by solid fuel or gas

are also in use. In addition to producing spirit, distil-

lation processes produce a large quantity of stillage,

which is processed into various by-products, such as

dark grains and distiller’s solubles.

Maturation

0018All whiskies are matured, and most legal definitions

of whisky incorporate a minimum maturation period.

The legal minimum varies from 1 year for some

American grain whiskies to 3 years for Scotch, Irish,

and Canadian whiskies. In effect, these are the min-

imum requirements, and most spirits are matured

for longer periods. Branded products are generally

matured for between 4 and 8 years, whereas single

malts and premium straight whiskies are matured for

8 to more than 18 years. The process of maturation

involves storing the raw spirit from the still, diluted to

50–80% ethanol, in barrels made from a limited

range of oak woods. The type of cask used greatly

affects the properties of the mature spirit. American

straight whiskies (e.g., Bourbon) are matured in new

charred American oak barrels that by law cannot be

reused. Maturation in new charred casks is associated

with an increase in color, solids, acids, esters, alde-

hydes, and tannins, together with increases in sugars,

such as arabinose, glucose, and xylose. (See Carbohy-

drates: Classification and Properties; Tannins and

Polyphenols.) New charred casks give a strong sweet,

wood-derived flavor to the final product. The casks

used for straight whisky maturation are American

standard barrels (180 l) made from American white

oak. ‘White oak’ is a cooperage trade classification

used for at least 10 oak species, the principal species

being Quercus alba.

0019Most other types of whisky are matured in barrels

previously used either for maturation of Bourbon or

in sherry production. Bourbon barrels may be used

‘as is’ or reassembled as hogsheads, with additional

staves and new ends to increase capacity (250 l).

Reuse of casks decreases the levels of wood compon-

ents extracted during maturation and gives a much

less intense wood-derived flavor. Sherry casks used

for the maturation of some whiskies are generally

butts or puncheons (480–520 l), which have been

used for the fermentation and/or aging of various

styles of sherry. Sherry casks can be either American

or Spanish oak casks (predominantly Quercus pet-

raea and Quercus robur). American oak is generally

used for fino and amontillado sherries, whereas Span-

ish oak is used for oloroso sherry. For sherry casks,

distillers will specify the species of oak, whether the

cask is used for fermentation and the contact time

with maturing sherry, as all are known to affect the

final properties of the mature spirit. In all but Bour-

bon production, casks are reused until they are ex-

hausted, i.e., fail to produce a satisfactory change in

the spirit over an economical maturation period. The

life of a cask can be extended by removal of the old

char layer and refiring the cask. This regeneration

Spirit

still

Spent

lees

Low wines

and

feints safe

Wash

still

Wash safe

Low wines and feints

Pot ale

Wash

Low wines and

feints

receiver

and charger

Intermediate

spirit

receiver

Wash

back

Wash

charger

Wash

preheater

Pot ale

receiver

fig0002 Figure 2 Typical malt distillery flow diagram. From Nicol D

(1989) Batch distillation. In: Piggott JR, Sharpe R and Duncan

REB (eds) The Science and Technology of Whiskies, pp. 118–149.

Harlow, UK: Longman Scientific and Technical, with permission.

WHISKY, WHISKEY, AND BOURBON/Products and Manufacture 6175

increases the levels of wood polymer breakdown

products extracted during subsequent maturation,

but does not regenerate all wood constituents, and

such casks give different sensory properties when

compared with a new cask.

0020 Maturing whisky was traditionally stored in stone-

built warehouses located beside the distillery. Casks

were stored in racks or in ‘stows,’ two or three high

on the earth floor. Expansion in production resulted

in much larger warehouses with steel racking, which

allowed casks to be stored up to 12 high. The

temperature and humidity within warehouses vary

between different countries, and this can affect the

way in which a spirit matures. In cool damp climates,

such as Scotland and Ireland, more ethanol than

water evaporates from the cask and consequently

strength decreases during the maturation period. In

warm dry climates, such as the USA, more water than

ethanol evaporates and strength increases. During

maturation, many of the chemical changes that

occur are influenced by the storage conditions,

particularly temperature. However though higher

maturation temperatures have been shown to in-

crease the rate of extraction of wood components,

this does not generally correlate with improvements

in sensory quality.

Blending to Bottling

0021All whiskies are to some extent blended. Even in the

most tightly controlled environments, batch-to-batch

variations can occur at any stage in the production

process. Blending is used to produce a consistent

product that has the distinctive flavors of that particu-

lar brand. For Bourbon and single malt production,

variations are evened out to create the recognized

brand from different batches of whisky. True blended

whiskies consist of light bodied spirits mixed with a

number of heavier bodied spirits in a wide range of

proportions. ‘Light-bodied spirits’ are those distilled

to high ethanol concentrations using continuous

column stills and include Scotch grain and American

light whiskies. ‘Heavier bodied’ whiskies are either

Condenser

Water jacket

Shell

Condenser

tubes

Syphon

Tail

Pipe

Water

Cradle

Shoulder

Charging

line

Air

vent

Water

Seal pot

Lyne

arm

Head

Sight glass

Swan neck

Ogee

Man door

Flue

plate

Crown

Steam coils

fig0003 Figure 3 Plain wash still. From Nicol D (1989) Batch distillation. In: Piggott JR, Sharpe R and Duncan REB (eds) The Science and

Technology of Whiskies, pp. 118–149. Harlow, UK: Longman Scientific and Technical, with permission.

6176 WHISKY, WHISKEY, AND BOURBON/Products and Manufacture

batch pot still products or column still products dis-

tilled to lower ethanol concentrations. The nature

and components of blends are determined by the

traditions and regulations of the country of origin.

In Scotland, there are a large number of distilleries,

and blend recipes are complex with as many as 50

malt whiskies used. Purchasing or exchanging new

whiskies by producers maintains the complexity of

these blends. In North America, where there are

fewer distilleries, and trading between competitors is

uncommon, the variety of whiskies for blending can

be increased by variations in mash bills, fermentation

conditions, distillation parameters, maturation

periods, and cask types.

0022 The physical process of blending is, however, very

similar. Approved whiskies are drained from casks

into passivated steel troughs, which convey the

whisky to a blending vat. Mixing uses mechanical

agitators and compressed air. When the blend is cor-

rect, deproofing water is added to reduce the alcohol

content to bottle strength. In Scotland, blending is

sometimes followed by a further maturation or

marrying period to allow integration of the individual

components into the final product. An additional

maturation or finishing period is also used for some

single malts. This frequently employs a distinctive

wood type, such as port casks, and is used to add

complexity to a whisky or to increase the number of

styles available from a single distillery.

0023Most whiskies are filtered prior to bottling to

reduce the risk of haze formation during storage. In

heavier bodied older whiskies and whiskies matured

at high strengths, high-molecular-weight lipids and

wood components slowly flocculate when the whisky

is reduced to bottling strength. This is controlled by

chill filtration, where whisky is cooled to between

10 and 10



C for a specified period of time, and

the problem compounds are removed by physical

separation and adsorption by a filter. The conven-

tional filter is a plate and frame filter with preformed

pads of cellulose, or cellulose impregnated or pre-

coated with diatomaceous earth. Operational param-

eters depend on the batch size, the nature of the

product, and the filtration rate required.

See also: Amino Acids: Properties and Occurrence;

Barley; Barrels: Wines, Spirits, and Other Beverages;

Brandy and Cognac: Armagnac, Brandy, and Cognac

and their Manufacture; Carbohydrates: Classification

and Properties; Flavor (Flavour) Compounds:

Structures and Characteristics; Lactic Acid Bacteria;

Phenolic Compounds; Rum; Rye; Sherry: The Product

and its Manufacture; Starch: Structure, Properties, and

Determination; Tannins and Polyphenols; Wheat: Grain

Structure of Wheat and Wheat-based Products; Wines:

Production of Table Wines