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(Table 4). Hops with perceived high-quality aromas

can command a premium price in the marketplace.

This is in contrast to hops sold for bitterness, where

trading is often carried out on a kilogram a-acid

basis.

0011 Foam The chemical structure of the iso-a-acids is

conducive to beer foam stabilization. Beer foam is

predominantly made up of malt-derived polypep-

tides, and the iso-a-acids can cross-link these poly-

peptides to provide a more stable foam structure.

Furthermore, the foam that adheres to the inside of

a beer glass during consumption – the lacing or cling –

is reliant on the presence of iso-a-acids in beer.

0012 Antibacterial potency The initial reason for adding

hops to beer – to stabilize it against flavor deterior-

ation – is well founded. At levels found in beers and at

the pH of beer (c. 3.9–4.5), the iso-a-acids effectively

kill many Gram-positive bacteria. This bacteriostatic

effect is aided by the presence of ethanol. Given the

global trends for increased beer pH and decreased

bitterness of beer, there is a school of thought that

considers that this mode of beer protection could be

compromised. In any case, other measures, such as

good brewery hygiene, sterile filtration, and pasteur-

ization also help to insure that beer is not affected by

microbial action.

Hops and Beer Production

0013 The traditional use of hop cones themselves meant

that a significant quantity of leaf material needed to

be removed from the wort after the boiling stage. This

was done with a hop back, a specifically designed

sieve to clarify the wort. The widespread use of pellets

and extracts means that, today, the hop back is absent

from many modern breweries. Alternative clarifica-

tion procedures were therefore required, particularly

for the remains of pellet powder. Based on an initial

discovery by Einstein, the whirlpool was developed.

This is a vessel whereby the wort, after boiling, is

pumped in tangentially. The circular motion of the

liquid results in the deposition of solids (trub) in the

center of the vessel, where it sinks to the bottom. This

development signified the beginning of hop-pellet

penetration into the brewing industry.

0014The presence of polyphenols in hops also assists in

the precipitation of excess polypeptides extracted

from the malt. If this precipitation is limited, there

is an increased risk of the final beer producing a haze

during its shelf-life. These polyphenols are also

attracting interest because of their antioxidant prop-

erties, although, as yet, the complexity of these

components in hops means that few specific details

on their properties are known.

Quality-control Aspects of Hops

0015Hops and hop products purchased principally for bit-

tering the final beer are assayed for a-acids. Today, this

is commonly achieved by high-performance liquid

chromatography (HPLC), although traditionally, this

was carried out using spectrophotometry or the meas-

urement of the so-called lead conductance value. For

aroma attributes, judgements are primarily on the

basis of the name of the variety: there is no specific

test available for predicting hop aroma performance.

The time-honored approach of rating hops according

to their visual characteristics and the aroma released

on rubbing hop cones in the hands is still very much

in use.

0016Hops and hop products should be stored cold (but

above 0



C), and, where possible, sealed packages

should not be breached until the contents are required.

Both aroma and bittering components of hops are

sensitive to heat and oxidation, although there

is some varietal dependence of the rate of hop degrad-

ation during storage. (See Chromatography: High-

performance Liquid Chromatography.)

Cereals

0017Cereals form the basis of beer. Although quantites

vary, for a typical beer, some 200 g of cereals per

liter of beer are used during production. Cereals pro-

vide the carbohydrates and amino acids necessary for

the yeast to grow, generate ethanol and carbon diox-

ide, and produce key flavors in the final beer. Malted

wheat and rye are used in some German beers, and

malted sorghum is used in some African beers. Raw

cereals, in the form of flour or grits, and cooked

cereals, generally as flakes or torrified (syn. torrefied)

tbl0004 Table 4 Common hop varieties widely available to brewers, in

decreasing order of tonnage (these varieties account for > 60%

of all hops produced in 2000)

Hop variety Growing areas

Qingdao Flower China

Nugget USA, Germany, Spain

Perle Germany, (USA)

Hallertauer Magnum Germany, (Spain)

Galena USA

Willamette USA

Zatec/Saaz Czech Republic, Slovenia

Spalt Select Germany

Hersbruck Germany

Hallertauer Tradition Germany

Zeus USA

Northern Brewer Germany

Countries in brackets are very minor growers of variety indicated.

Source: The Barth Report (2000/2001).

BEERS/Raw Materials 425

are still widely used as adjuncts to form part of the

grist. Today, most brewing malt (with the exception

of some specialist beers made from wheat malt) is

made from barley, since it has been recognized that

in certain essential properties, barley is superior to

many other cereals. In any case, with the exception of

the Japanese happoshu beer brands, which may use

as little as 25% malt in the grist, barley malt makes

up at least 40% of the total grist. Nevertheless, per-

haps with the exception of the Japanese brewing

industry, the proportion of extract derived from

malt remained essentially constant over much of the

twentieth century.

0018 Malted barley, as well as adjuncts and syrups, are

usually assessed for extract yield. This is the quantity

of sugars released per unit mass of malt, adjunct, or

syrup. This extract yield relates directly to the quan-

tities required and therefore the impact on cost. Ex-

tract yield, though, is measured by density and reflects

the total sugar content. However, a proportion of the

sugar content is nonfermentable, and this is assessed

by a further measurement – that of fermentability.

This is determined by carrying out a test fermentation

and measuring the maximum amount of extract con-

sumed. Again, this is done by density measurements.

The remaining sugars are termed dextrins. Whilst

they may not contribute directly to the yield of etha-

nol, dextrins may have a subtle role to play in the

sensory qualities of the final beer. Two other common

measurements are the total nitrogen content, a meas-

ure of protein content, and, in malt, S-methylmethio-

nine. The significance of the latter is that it is readily

degraded to yield dimethyl sulfide, a distinctive sulfur

compound, with an aroma reminiscent of sweetcorn.

At the correct levels, it is a key flavor impact com-

ponent of many beers, particularly lager-style beers.

For pale malts, the levels of enzyme activity – espe-

cially a- and b-amylase, are important parameters for

satisfactory performance of the malt in the brewery.

Typical analytical data for various cereals and their

products are given in Table 5.(See Cereals: Contribu-

tion to the Diet.)

Barley

0019The most popular cereal is barley that has been

malted. Its use has several advantages: it has a suit-

able level of protein (8–12% dry weight) and low

levels of lipids, it develops high levels of amylolytic

enzymes during germination, and it has a husk that

assists in the separation of insoluble material from the

required extract.

0020Barley is essentially a temperate plant that is never-

theless distributed widely in both tropical and sub-

tropical zones. The main commercial growing areas

of barley are in the grassland belt, across the northern

hemisphere from the northern USA and Canada,

across northern Europe into Asia and North Africa,

where it probably originated. Again, in the southern

hemisphere, barley is grown commercially in South

America, on the fertile uplands of South Africa and in

Australia and New Zealand. (See Barley.)

0021Barley malting The malting of barley has several

purposes. Firstly, the development of amylolytic

enzymes is essential for the subsequent brewing oper-

ation, as these are required for the formation of fer-

mentable sugars from the malt starch. This diastatic

power is more than enough for conventional brewing,

so this can be diluted to some extent with nondia-

static materials, such as syrups and speciality malts.

Secondly, on a practical level, it is desirable to reduce

or eliminate the b-glucans present in barley. These

form gels that substantially slow down or even stop

the separation of the sweet wort from the residual

solid material. Thirdly, there needs to be enough

free amino acids released, either during malting or

in the mashing stage of beer production, to support

the yeast growth required during the early stages of

fermentation. Finally, in terms of flavor, ‘grainy’ or

‘green’ flavors should be eliminated, to be replaced

by desirable ‘malty’ flavors. Other aspects are assum-

ing importance, namely the reduction in levels of

agrochemical residues during malting, which in turn

means lower levels finding their way into the final

tbl0005 Table 5 Typical malt specifications

Parameter Level Applicability

Malt

Moisture (%, w/w) 5 To ensure storage stability

Hot water extract (l



1

) 310 Indicates the amount of soluble extract available

Color (



EBC) 3 Has a large impact on final beer color

S-Methylmethionine (mg kg

1

) 4.5 Indicative of likely dimethyl sulfide levels in final beer

Total nitrogen content (%, w/w) <1.65 Ratio with soluble nitrogen gives an indication of the degree of malting (modification)

Total soluble nitrogen (%, w/w) 0.70 Indicates the amount of soluble nitrogen (protein)

Free amino nitrogen (mg l

1

) 140 Indicates the degree of proteolysis during malting

426 BEERS/Raw Materials

beer. This also applies to the presence of barley micro-

flora, which can be accompanied by a range of myco-

toxins.

0022 The malting process involves several stages. The

malt, once produced, is considered to be relatively

stable if the grain moisture levels are below about

12% (w/w), and can be stored under appropriate

conditions for many months. Low atmospheric mois-

ture and attention to possible fungal growth are es-

sential during prolonged storage. The final malt color

will depend on the kilning regime used to dry the malt

so that it is stable during storage. Thus, so-called lager

malts are dried at temperatures well below 100



whereas an ale malt is dried at around 100



C. These

higher temperatures stimulate nonenzymic browning

reactions between sugars and free amino compounds,

thus resulting in a darker color and, generally, a

higher degree of flavor. Crucially, though, both still

retain enzyme activity essential for the mashing oper-

ation. The degree of enzyme development is termed

‘modification’ and has an impact on how the malt is

used in the brewery.

0023 Brewing with malt The early stages of beer produc-

tion have been tailored to the properties of malt.

Thus, to effect recovery of as much brewing value as

possible from the malt, it must be ground, and the

enzymes generated during malting need to be acti-

vated (Table 6). There are some variations on the

milling and mashing operations, but essentially,

milled malt is blended with water in a specific ratio,

typically 1:3 (w/w).

0024 Specialty malts Some beers are brewed with rela-

tively low concentrations of specialty malts. Gener-

ally, these retain little enzymic activity, but are used

because of the specific flavor or color attributes that

they confer on the final beer (Table 7). Whilst not a

malt, roasted barley may also be considered, together

with specialty malts, as it is used for similar reasons.

Many darker beers contain small percentages of

specialty malts as part of the grist.

Adjuncts

0025This is a term reserved for nonbarley malt derived

cereal substitutes in beer production. Whilst barley

malt is best tailored to the requirements of brewing,

there are good reasons for partial substitution of

barley malt for other cereals. These include flavor

modification, increasing brewery capacity, poten-

tially favorable costs (malting barley often commands

a premium price), enhancing the stability of the final

product with respect to haze formation, and as a point

of beer brand differentiation (e.g., oatmeal stouts,

wheat beers). The lack of diastatic power in adjuncts

is not usually a serious issue as good-quality malt is

characterized by having amylolytic activity surplus to

requirements. As a rule of thumb, there is little need

to be concerned about the final diastatic power if the

level of diastatic malt in the grist is at 70% or higher.

0026Adjuncts come in a variety of forms. Some of these

forms generally require a specific brewery plant, the

installation of which implies a future commitment to

the chosen adjuncts. A brewer therefore needs to be

tbl0006 Table 6 Some enzyme activities present in milled malted barley during mashing

Type Enzyme Activity

Amylases a-Amylase An endoenzyme, mainly responsible for the breakdown of high-molecular-weight

starch

b-Amylase An exoenzyme that releases maltose

Limit dextrinase Breaks down branch points of starch

a-Glucosidase An exoenzyme that releases glucose

Proteases Endopeptidases A sulfydryl protease of general activity

Exopeptidases Important for free amino nitrogen generation

Aminopeptidases Exopeptidase that attacks the amino end of protein

Carboxypeptidases Most important proteases, attacking the carboxyl end of protein

Other carbohydrases b-Glucan solubilase Releases b-glucan from cell walls

Endo-b-glucanases Break down potentially troublesome b-glucans

Pentosanases (xylanase) Degrade pentosans

Xylosidase Breaks down xylan polymers

tbl0007Table 7 Typical color and flavor descriptor attributes of

specialty malts

Specialtymalt Color Typical flavor characteristics

Pale malt 4.5–4.8 Biscuit-like

Caramalt 25–35 Sweet, nuitty, cereal, toffee

Crystal 100–300 Malty, toffee, caramel

Amber 40–60 Nutty, caramel, fruity

Chocolate 900–1200 Mocha, treacle, chocolate

Black 1250–1500 Smoky, coffee

Roasted barley

1000–1550 Burnt, smoky

Not strictly a malt, but included here for completeness.

BEERS/Raw Materials 427

sure that the source of required adjunct is and will be

available at the required quality for the foreseeable

future.

0027 Raw cereal grains In principle, suitably milled

barley, wheat, rye, and Triticale grains can be used

during mashing without prior treatment. Of these,

most interest has focused on the use of whole barley.

Careful milling of the cleaned barley, preferably

retaining the husk as intact as possible, provides a

suitable grist addition. Hammer milling of raw cereal

grains is generally avoided, as problems with

b-glucan extraction and subsequent run-off difficul-

ties can occur. If the proportion of raw barley in the

mash is high, enzyme supplementation is highly desir-

able to degrade the proteins and carbohydrates pre-

sent. As a total replacement for malt, raw barley is

financially attractive, although a balanced mixture of

enzymes is essential to give the required extract for

subsequent fermentation.

0028 Cooked intact cereal grains Roasted barley, torre-

fied or micronized barley, and wheat grains contain

no active enzymes. However, their preheating results

in partly precooked starch and a disrupted grain

structure. Such products are readily milled and easily

handled, giving extracts generally higher than those

for raw cereals. The heat also partly degrades

b-glucans, so that the resulting worts from torrefied

grains are less viscous than those from raw materials.

0029 Grits Grits may be defined as uncooked, nearly pure

fragments of starchy endosperm from cereal grains. If

they are used directly in the brewery, they must be

cooked or flaked (see below). The removal of other

parts of the grain reduces the levels of lipid, ash, and

fiber. Rice grits, or broken rice, are often a byproduct

of debranning and milling rice for human consump-

tion. Nowadays, milling efficiency has improved

such that less of this byproduct is produced. Rice

grits are generally low in lipid and fiber but must be

cooked well if adequate extract is to be recovered.

There are substantial differences in the suitability of

various rice cultivars for beer production, but rice is

considered to be flavor-neutral and is therefore a

popular adjunct.

0030 Maize grits are the most common adjunct used in

the USA. They can be prepared in a number of ways,

but in any case, the aim is to remove the outer layers

and the lipid-rich germ. The resulting grits are rich in

starch and contain much less lipid than their parent

grain. They are popular, as, after cooking, they yield a

good extract during mashing.

0031 For use in the brewery, all grits must be cooked to

disrupt them and gelatinize the starch. They are then

usually mixed with conventional barley malt mash to

complete the starch conversion. The grits are mixed

with a small proportion of highly diastatic malt or

with microbial amylase and then heated. Tempera-

tures may be raised to boiling or cooking can be

carried out under pressure to effect gelatinization.

The swollen and gelatinized starch is partly degraded

or liquefied before the heat inactivates the amylase

activity. Consequently, viscosity neither increases to

unmanageable levels nor sets to a gel on cooling. This

is important from a practical point of view, as it can

be pumped and does not burn on to the heating

surfaces. Such burning can lead to problems such as

flavor pick-up, color generation, and deteriorating

heat-transfer characteristics.

0032Flaked cereals These are produced either by

cooking whole grains with steam or by microniza-

tion. In both cases, the heated grain is passed through

feed rolls to flaking rolls, typically held at 85



C. For

the more traditional steam process, the flakes are

dried prior to packaging. The flakes may also be

lightly crushed, as the flakes themselves have a low

bulk density. Because the starch is already gelatinized,

the flakes do not need cooking and can be added

directly to the mash. Flakes also produce relatively

little soluble nitrogen, so they can be used as a wort

nitrogen diluent.

0033A range of cereals are flaked. Whilst flaked rice is

popular because of its good extract yield and neutral

flavor and color, it is not used for economic reasons.

Flaked maize grits and flaked whole wheat grains and

barley grains are currently in use.

0034Flours In principle, both wheat and barley can be

hammer-milled in the brewery to produce coarse

flours. These are suitable for addition directly into

the mash. Nevertheless, flour milling is a rather

specialist process, and in practice, the brewer buys

flour from certain suppliers.

0035Syrups Sucrose, and its hydrolysis product, inverted

sugar, are used by some brewers during beer produc-

tion. Produced either from sugar cane or sugar beet,

the range of products available is large, in terms of

color, mineral content, and residual syrup present.

They can be supplied for the special flavors that

they can confer. These can include descriptors such

as burnt, raw sugar, and bland.

0036Syrups and sugars from the partial or essentially

complete hydrolysis of refined maize starch, unlike

beet or cane syrups, contain no significant quantites

of nitrogenous components or other yeast nutrients.

Thus, like sucrose syrups, they are wort extenders

rather than wort replacers. Their production requires

428 BEERS/Raw Materials

two hydrolytic stages. The first is the solubilization of

starch slurry to form dextrins. Here, the starch is

completely solubilized, so much so that it does not

form gels or retrograde (precipitate) on cooling. In the

second stage, the dextrins of the first stage are con-

verted into the desired spectrum of sugars. Dilute

mineral acid and enzymes can be used in both stages

to accurately control the desired result. (See Syrups.)

0037 Malt extracts and wort-replacement syrups Malt

extracts are essentially sweet wort (i.e., unhopped),

from which the water has been removed under re-

duced pressure. Although the extracts may be either

diastatic or nondiastatic, the former are rarely, if ever,

used. Malt extracts are an expensive source of

extract, because the malt itself is relatively expensive,

as are the operations for water removal.

Summary

0038 The hop- and beer-production industries are, for the

foreseeable future, inextricably linked, as there is no

viable alternative to hops that brewers can employ

and few, if any, other outlets for hops other than

brewing. Like hops, cereals are essential to beer, and

indeed, the two have been intimately linked ever since

beer was first produced. Specific barley varieties are

bred and tested for their performance in all aspects of

agronomic, malting, and brewing characteristics.

See also: Beers: History and Types; Wort Production;

Chemistry of Brewing; Caramel: Properties and Analysis;

Cereals: Contribution to the Diet; Chromatography:

High-performance Liquid Chromatography; Malt: Malt

Types and Products; Chemistry of Malting

Further Reading

Bamforth CW (1998) Beer – Tap into the Art and Science of

Brewing. London: Plenum Press.

Barth HJ, Klinke C and Schmidt C (1994) The Hop Atlas.

Nuremburg: Joh. Barth & Sohn.

Briggs DE, Hough JS, Stevens R and Young TW (1994)

Malting and Brewing Science, Volume I, Malt and

Sweet Wort, 2nd edn. London: Chapman & Hall.

Corran HS (1975) A History of Brewing. Newton Abbot,

UK: David & Charles.

Hough JS, Briggs DE, Stevens R and Young TW (1993)

Malting and Brewing Science, Volume II, Hopped

Wort and Beer, 2nd edn. London: Chapman & Hall.

Hughes PS and Baxter ED (2001) Beer: Quality, Safety and

Nutritional Aspects. Chemistry: Royal Society of

Chemistry.

Kunze W (1999) Technology – Brewing and Malting, Inter-

national Edition. Berlin: VLB Berlin.

Neve RA (1991) Hops. London: Chapman & Hall.

Verzele M and de Keukeleire D (1991) Chemistry and

Analysis of Hop and Beer Bitter Acids. London: Elsevier.

Wort Production

M Ortega-Heras and M L Gonza

lez-Sanjose

University of Burgos, Burgos, Spain

Background

0001One of the most common and simple definitions of

beer is: ‘beer is the drink resulting from the fermenta-

tion by means of selected yeast of the wort, which is

obtained from malted barley, alone or mixed with

other starch sources, and it is flavored by boiling

with hop flowers.’

0002Brewing process can be divided into three phases:

malting, wort production and fermentation, and

maturation. Starting with the malting process, this

includes different phases, such as steeping, germin-

ation, drying, and toasting. In this way, barley is

transformed into malt.

0003During these phases, barley undergoes the

following changes:

0004Steeping: The barley grain is humidified in large

tanks of water into which air is bubbled to prevent

anaerobic conditions developing. The temperature

is also controlled. When this phase ends, the barley

grain has a humidity of between 42 and 46%.

0005Germination of the grain: This involves partial

development of the embrion, activating several

endogenous enzymatic systems, such as the a-

and b-amylases and the proteases, which are

capable of hydrolyzing the starch and proteins,

respectively. This germinated barley is known as

‘green malt.’

0006Drying and toasting: In this phase, the grain is

dried, the embrion is destroyed, and the enzymatic

activity is stopped to avoid using up the reverse

substances. In this way, the malt is obtained.

The aroma and taste of the toasted grain are formed

simultaneously by Maillard reactions. The beer color

is lighter or darker depending on the toasting of the

malt.

0007The second phase includes different processes that

convert malt into wort. Wort is a liquid extract con-

taining fermentable sugars (sweet wort), amino acids,

vitamins, and other compounds, and it is the principal

substrate in which beer is obtained by fermentation.

BEERS/Wort Production 429

Before fermentation, the wort is boiled with hop

flowers to flavor it (sweet hopped wort).

0008 The third phase is associated with wort fermenta-

tion and maturation, a process in which yeast trans-

forms the wort into beer, by consuming sugars and

releasing ethanol and CO

. This phase ends with the

filtration process, to produce a clear beer, and then

bottling.

0009 Nowadays, only some breweries have their own

malt factory, and most of them have to buy the

malt, as well as several other raw materials. In such

cases, the first stage of the brewing process is wort

production.

Wort Production

0010 During this phase, malt and other starch sources (ad-

juncts) undergo different processes, in which the main

aim is to obtain a fermentable extract, the wort.

0011 Adjuncts are used in order to reduce the quantity of

malt used, since malt is more expensive than these

products, and so the use of adjuncts in relatively large

amounts (20–30%) significantly reduces the cost of

the brewing process. The most common adjuncts are

rice, corn, wheat, or even sugars, syrups, and liquid

starches, etc.

0012 It is important to note that some legislation, espe-

cially European legislation, does not permit the

addition of exogenous enzymes during the brewing

process. Therefore, the use of malt is essential in

order to obtain a fermentable extract, because when

the exogenous enzymes cannot be used, malt is the

only source of enzymatic activities, as will be shown

later.

0013 However, some special beers, such as wheat beers

or sorghum beers (very common in African countries)

are produced without the use of malt. In these cases,

cereals are previously malted in a process similar to

that for barley, or exogenous enzymes are usually

added during mashing. The most recent adjuncts

described are ‘chufa nuts’ or sedge tubers, which,

after commercial enzymatic treatment, produce a

wort comparable with sorghum wort, which may

even have a better filterability, probably because of

its higher fiber content.

0014 In most of the cases adjuncts arrive at the brewery

in a ready-to-use state, usually in the form of flour or

other similar product, or may even be pretreated by

different processes such as micronization, extrusion,

etc. In this way, they can be used without reducing

their particle size, and pretreatment gelatinizes the

starch, so that their transformation into a liquid fer-

mentable extract is easier.

0015 Recently, a study on the use of nonmalted barley

has been published, in which barley was gelatinized

by cooking and thus was able to replace up to 10% of

the malt, and extruded barley substituted up to 50%

of the malt. However, barley treated previously with

commercial enzymes did not yield satisfactory results.

0016The process to convert malt into wort comprises

several stages as can be seen in Figure 1.

Malt Milling

0017Malt or other malted cereals (e.g. sorghum) arrive at

the brewery as a complete kernel, so the first process

is malt milling, which is carried out in order to reduce

the size of the particles, thus facilitating extraction

and transformation of the desired compounds.

0018This process involves separating the endosperm

from the husk and reducing the particle size to yield

thick seeds, fine seeds, and mainly flour. However, it is

important that the husk remains as intact as possible,

so as to act as a natural filter during the filtration

process.

0019The most commonly used milling system is the

roller mill, generally consisting of three pairs of

rollers. Placed between the rollers these are a series

of sieves that separate the grist fraction by size. The

final product of the milling process can be classified

as follows:

0020Husks: These are the largest particles and consist

of the outer case of the barley grain. They contrib-

ute very little to the wort.

Malt

Milling

Filtration

Separation of

precipitates

Cooling of the wort

aeration

Boiling

Hops

ExtractionWater Adjuncts

Sweet hopped wort

fig0001Figure 1 Process of wort production.

430 BEERS/Wort Production

2.0021 Thick particles: These contain the least modified

endosperm. They account for 20–25% by weight

of the milled malt and yield 10–12% of the soluble

extract.

0022 Fine particles or flour: These contain the most

modified endosperm. They account for 50–60%

by weight of the milled malt and yield 89–90% of

the final extract.

The milling system must be adjusted in order to

improve the production of fine particles, without

fractionating the husk. In this sense, malt is some-

times steam-treated to increase the moisture of the

husk, which remain then more elastic and is more

difficult to fragment.

0023 The next process is mashing, in which the liquid

extract is obtained.

Mashing

0024 Once the malt has been milled, it is mixed with water

to form the ‘mash.’ The mash is heated under con-

trolled conditions, and then important transform-

ations of the malt components are carried out by the

action of endogenous malt enzymes.

0025 After the hydration process, the enzyme activity

that was latent in the dry malt is renewed. Enzymes

work best under the following conditions: abundant

water (high water activity), high-surface-area par-

ticles (allowing better access to their substrates, i.e.

starch, proteins, lipids, etc.), and optimum tempera-

tures, which are reached in subsequent stages.

0026 A recent study has shown that during mashing, it

is very important to control the oxygen availability,

since some of the enzymatic systems that could

be activated during this step are oxygen-dependent.

Furthermore, the presence of oxygen determines

the development of nonenzymatic oxidation, which

can be very important in the formation of undesir-

able products such as aldehydes formed from un-

saturated fatty acids or the formation of brown

pigments.

0027 The mashing phase is usually carried out in a single

vessel, lasts between 4 and 6 h, and is often carried

out in accordance with a particular temperature

profile, since each type of enzyme has its optimum

working temperature:

0028 35–50



C: Dominated by the action of proteases

and phosphatases. Proteins are hydrolyzed, and

amino acids and other nitrogen compounds are

released.

0029 50–65



C: Dominated by the action of the b-

amylases, which convert starch into maltose and

limiting dextrines.

003065–75



C: a-Amylase activity is dominant. Starch

hydrolysis continues, and its saccharification is

completed.

0031>75



C: All enzymes in the mixture are rendered

inactive.

The exogenous enzymes can be added sequentially at

each stage or at the beginning as a complex mixture

that usually contents proteases and amylases.

0032Different breweries apply different extraction

methods. The three most commonly used methods

are described below.

Infusion Mashing

0033This is the traditional method employed in the manu-

facture of English ‘ale.’ The method uses a single

vessel, and mashing is carried out at a single tempera-

ture, known as the conversion temperature, usually

within 62–67



C. This extraction method requires

well-modified or broken-down malts. It is not

suitable for use with additional starch sources that

require prior gelatinization.

Decoction Mashing

0034This is the traditional method for making ‘lager’ beer.

The equipment used for this type of process include a

mash tun, a mash cooker, and a filter vat.

0035In this process, part of the mash is pumped into a

second vessel, heated to boiling temperature, and re-

added to the main mash. In mixing the two parts, the

whole mash reached the different expected tempera-

tures. This method is especially suitable for use with

malts that have not been broken down to any large

degree or are only slightly modified.

0036The traditional system uses three decoctions (the

Pilsen method), in which the temperature is raised in

three steps (34–40



C, 50–65



C, 75



C). This system

has been replaced by a double and finally a single

decoction, since malts used nowadays are more

modified.

0037This decoction procedure can also be applied to

adjuncts in which the starch usually has a gelatiniza-

tion temperature higher than that of the malt starch.

Double Mashing

0038This is the traditional method used in the USA. The

adjuncts, which represent 30–50% of the total

extract required and 10% of the malt or an external

source of a-amylase, are heated in a mash cooker to



C and maintained at this temperature for a speci-

fied period of time.

0039The temperature is then raised to the boiling point

and maintained for 20 min under these conditions.

After a while, the part that is removed and boiled

off is pumped into the mash tun, which has been

BEERS/Wort Production 431

kept at 35–40



C. The temperature of the mixture is

controlled by the speed of pumping.

0040 Recent studies have focused on the use of different

exogenous enzymatic systems in order to improve the

quality of the wort during mashing, such as studies in

the use of a new purine-nucleosidase to reduce the

levels of purine nucleosides of worts and the use of

proteinases to stabilize the foam.

0041 Moreover, several studies on the thermostability of

endogenous enzymes of different varieties of barley,

an important factor for the malting and mashing

process, are being carried out, in order to determine

the best varieties for the brewing process. It is inter-

esting to note that some breweries usually add some

selected Lactobacillus spp. to increase the acidity of

the mash and wort.

0042 After mashing, all desired compounds are ex-

tracted and transformed into their respective bypro-

ducts, thus yielding a fermentable extract. However,

this extract is cloudy, with a large amount of solids in

suspension, so filtration is required to separate the

liquid from the solid particles.

Filtration

0043 In this phase, the insoluble part of the mixture, the

spent grain, is separated from the liquid part, the

‘sweet wort’.

0044 Filtration is usually carried out using a lauter tun or

by a mash filter (filter press). The lauter tun is a vessel

with a flat, perforated bottom. First, the husk rapidly

forms a filter cake on the bottom, which contains a

natural filter through which the wort can be filtered.

This filter yields wort of an excellent quality, but the

filtration time is long, and it presents several prob-

lems in terms of removal of the spent grain. There is a

special type of lauter tun, the strainmaster, which has

a different bottom with slotted triangular pipes

instead of a perforated bottom. In this way, the filtra-

tion area is larger, and the run-off is quicker. The

quality of the wort is also good, but the filter cake

retains a large amount of liquid, and discharge is not

easy.

0045 Several hollow frames and plates, separated by

filter cloths, form the mash filter or filter press. In a

similar way to the lauter tun, when wort crosses the

filter, husk is retained on the frames forming the filter

cake. The wort obtained with this type of filtration

system is not as clear as that obtained using the lauter

tun, and the wort also has higher levels of lipids.

However, it is a more rapid process, and it is easier

to automate. Usually, mash filtration is carried out to

a high temperature in order to improve the filtration

process and reduce the duration. This step is very

important in the brewery; it could be considered one

of the limiting steps. Brewers and related commercial

industries have spent much time researching how to

develop fast filtration systems that do not result in

any losses of the wort quality. Some of the first stud-

ied systems were high-pressure mash systems, but the

filter in these types of system had several technical

shortcomings and did not meet the requirements.

Later, a membrane mash filter was developed. This

system yields wort of a good quality, and enables

good separation of the solid part, even when a fine

grist is used. Membranes can be inflated with com-

pressed air to remove more of the liquid remaining in

the filter cake, thus improving the extraction yield.

This system can be easily automated. In the early

1990s, different breweries installed this type of filter.

Another system developed at the beginning of the

1990s was the 2001 filter. This is an automatic system

equipped with polypropylene plates and a frame

filter, and comprising the following stages: filling,

filtration, precompression, sparging, compression,

and spent-grain removal. The advantages of this filter

include: production of a clear wort with a low fatty

acid content, reduced volume of sparging liquor, pro-

duction of a dryer spent grain, reduced O

uptake,

zero heat radiation and waste water, high efficiency

(12 brews per day), simplified milling technology,

flexible load (70–110% normal capacity), and flexi-

bility with regard to raw material and mashing pro-

cedures.

0046The final product of this step is more or less a

‘clean’ liquid extract called a ‘sweet wort.’

Wort Boiling and Addition of Hop

0047Wort boiling is carried out for different reasons,

which can be summarized in terms of the main effects

and secondary effects that are very important for the

final characteristic of the final beer, such as stabiliza-

tion, improve flavor, modify color, etc.

0048The main effects are: to render enzymes inactive,

once starch, proteins, and other constituents have

been transformed (hydrolyzed), and to sterilize the

wort, converting it into a sterile medium for the sub-

sequent fermentation.

0049Some of the most important secondary effects are:

0050Coagulation of the remaining proteins (hot break),

which is very important in preventing cloudiness in

the beer;

0051Precipitation of calcium phosphate, which causes a

fall in pH.

0052Extraction and transformation of important com-

pounds as boiling is carried out in the presence of

hop. Therefore, during this process, humulones

and lupulones are extracted, and then, after heat

432 BEERS/Wort Production

treatment, they are isomerized to give the typical

bitter taste of beer. In addition, the isoacids formed

help to stabilize the foam.

0053 Removal of volatile products (e.g., undesirable

flavor compounds such as sulfated compounds)

and some of the essential oils extracted from the

hop.

0054 Partial caramelization of the wort sugars and the

formation of Maillard reactions products, im-

proving the flavor, and slightly changing the color.

Some of these products (e.g., melanoidins) induce

changes in the surface tension and also help stabil-

ize the foam.

0055 Partial oxidation of phenols and their condensation

with proteins. Therefore, they can be removed

more easily from the medium, the beer is more

stable, and cloudiness is reduced.

0056 Evaporation of water and wort concentration.

Boiling is traditionally carried out in boiling vessels,

where hop is added as hop flowers, pellets, or even

hop extracts. In the manufacture of ‘ale,’ the hops are

usually added in the initial stages of boiling, as for-

mation of foam can be controlled during the process.

In ‘lager’ production, the hop is usually added manu-

ally and at different times during the boiling process,

thus imparting a hop aroma. Different types of vessel

are used in the wort boiling process. The most

common types are as follows.

Traditional Boiling Vessels

0057 Open-top vessels, in which the process takes places at

atmospheric pressure. Traditionally, boiling vessels

were made of copper and had an external heat source.

Modern vessels have an internal heat source and are

made of stainless steel, which is a low heat conductor,

thus minimizing heat loss. However, some authors

claim that the traditional copper vessel seems to

impart a special flavor characteristic to the wort.

0058 In traditional systems, the boiling process lasts be-

tween 1 and 2 h. In order to reduce the energy needs

for this process, several heat systems have been

developed. The use of an external heat exchanger, or

calandria, requires a shorter boiling time, because, in

this system, the wort circulates through the heat

exchanger and reaches higher temperatures (106–

110



C).

0059 Other systems have focused on recycling the vapor

formed. Mechanical vapor-compression systems have

been used as external boiling systems.

Continuous High-temperature Systems

0060 Focusing on energy reduction, these systems consist

of several consecutive heat exchangers, in which the

wort temperature is increased to approximately

140



C and held for 3–5 min. The pressure is then

reduced using two expansion vessels, and the vapors

are finally recycled to heat the heat exchanger. In this

way, the brewing process time is reduced, and less

energy is consumed, so the final costs can be reduced

considerably. Several different systems, with diverse

designs, have been patented in recent years. Some

authors have indicated that there are remarkable dif-

ferences between the sensorial characteristics of the

worts produced by both methods.

0061The final product from the boiling step is called

‘sweet hopped wort,’ which must be filtered before

fermentation in order to eliminate all the precipitates

formed during boiling (hot precipitates).

Separation of Hot Precipitates (Filtration)

0062The first point to note is that after the boiling process,

all operations must be carried out under sterile condi-

tions in order to avoid any recontamination of the

wort.

0063Hot precipitates, together with hop flowers if they

have been used, must be removed from the medium.

In these cases, the hop flowers form a filter bed or

cake through which the wort is filtered. When pellets

or extracts are used, wort is usually clarified by the

addition of a clarifying agent, such as bentonite or,

even better, silica gel, before it is pumped into the

filtration systems. The types of equipment employed

in this filtration process include the so-called wind-

mill, Whirlpool, centrifuge, or hot settling tank.

0064Different modifications of the filter systems have

been developed in recent years, with the main aim to

improve the filtration process by reducing the oper-

ation time and increasing the cleanness of the sweet

hopped wort.

0065After hot filtration, the clean wort must be cooled

in order to reduce the temperature and to allow the

addition of yeast, and must be aired to promote the

growth of the yeast, so that the wort will be in the best

condition for the next step: fermentation.

Cooling and Aeration of the Sweet Hopped

Wort

0066There are several systems of cooling and aeration

used in beer manufacture. These include:

0067Flat recipients: In this traditional system, the wort

was loaded on to the recipients to a height of 25 cm.

Cooling was achieved by evaporation of the

water through ventilation holes through which air

flowing over the wort could enter. These containers

also allowed aeration of the wort and decanting of

hot and cold precipitates. The air used would be

BEERS/Wort Production 433

passed through aseptic filters that were free of un-

desirable microorganisms.

0068 Refrigeration by means of plate or tubular heat

exchangers: The cooling agent used is usually cold

water, or refrigerated glycolate, alcohol or brine.

Air is introduced, in the form of sterile air or

oxygen, usually between the two sections of the

plate heat exchanger, when the wort enters the

final stage of cooling. The fall in temperature

leads to the formation of new precipitates, which

are eliminated by sedimentation, although some

breweries do this by filtration or centrifugation

of the wort, or even by flotation separation,

which is more effective than sedimentation when

the particle size is very small. Furthermore, studies

carried out in 2000, showed that flotation tech-

niques minimize wort losses. Cross-flow, micro-

and ultrafiltration have also been described as

interesting techniques by which to eliminate the

wort cold break precipitates.

The aeration is usually controlled by specific mechan-

isms based on concurrent flow of the liquid and gas,

and on the residence time of the liquid in the treat-

ment unit.

0069 The final product is a clean, cold, and aired sweet

hopped wort, ready to be transformed into beer after

its fermentation by the action of selected yeast.

Special Wort

0070 Several patents have been developed in recent years

for the production of ‘special wort,’ such as ‘concen-

trate wort,’ which can be used as a raw material in

small breweries or in home installations common in

some countries such as the UK.

0071 In addition, special wort with lower levels of fer-

mentable sugars is used in the brewing process for

low-alcohol beers. Limiting the action of amylases,

especially b-amylase, reduces the production of fer-

mentable sugars. This can be achieved with a high-

temperature mashing process, in which b-amylase is

thermal destroyed by heat. This wort has a high level

of dextrin. Low-gravity wort is also employed in low-

alcohol beer manufacture. This type of wort is

obtained by low-gravity brewing or, more usually,

by diluting normal wort.

See also: Beers: History and Types; Raw Materials;

Chemistry of Brewing; Biochemistry of Fermentation;

Yeasts