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The Brewing Process
Work in the brewery is typically divided into 7 steps:
Mashing, Lautering, Boiling, Fermenting, Conditioning, Filtering,
and Filling.
Mashing
Mashing is the process of mixing milled grain (typically malted grain)
with water, and heating this mixture up with rests at certain temperatures
to allow enzymes in the malt to break down the starch in the grain
into sugars, typically maltose.
Large breweries usually employ a decoction mash method, in which
the thickest part of the mash is boiled to extract more starch from
the grain, then returned to the mash to achieve the next rest temperature.
These can be classified into one-, two-, and three-step decoctions,
depending on how many times part of the mash is drawn off to be boiled.
Smaller breweries use infusion mashing, in which the mash is heated
directly to go from rest temperature to rest temperature. Some infusion
mashes achieve temperature changes by adding hot water, and there
are also breweries that do single-step infusion, performing only one
rest before lautering. It is important to note that fancy equipment
and methods do not guarantee a good beer. Many wonderful beers are
produced on inexpensive, bare-bones equipment, and some bad beers
are produced in breweries that are state-of-the-art.
In large breweries, in which optimal utilization of the brewery equipment
is economically necessary, there is at least one dedicated vessel
for mashing. In decoction processes there must be at least two. The
vessel has a good stirring mechanism to keep the temperature of the
mash uniform, and a heating device which is efficient, but will not
scorch the malt, and should be insulated to maintain rest temperatures
for up to one hour. A spray ball for clean-in-place (CIP) operation
should also be included for periodical deep cleaning. Sanitation is
not a major concern before wort boiling, so a rinse-down should be
all that is necessary between batches.
Smaller breweries often use the boil kettle for mashing, or use the
lauter tun. The latter case either limits the brewer to single-step
infusion mashing, or leaves the brewer with a lauter tun which is
not completely appropriate for the lautering process.
Grain milling
The grain used for making beer must first be milled. Milling increases
the surface area of the grain, making the starch more accessible,
and separates the seed from the husk. Care must be taken when milling
to ensure that the starch reserves are sufficiently milled without
damaging the husk and providing coarse enough grits that a good filter
bed can be formed during lautering.
Grains are typically dry milled. Dry mills come in four varieties:
two-, four-, five-, and six-roller mills. Hammer mills, which produce
a very fine mash, are often used when mash filters are going to be
employed in the Lautering process because the grain does not have
to form its own filterbed. In modern plants, the grain is often conditioned
with water before it is milled to make the husk more pliable, thus
reducing breakage and improving lauter speed.
Two-roller mills
Two-roller mills are the simplest variety, in which the grain is crushed
between two rollers before it continues on to the mash tun. The spacing
between these two rollers can be adjusted by the operator. Thinner
spacing usually leads to better extraction, but breaks more husk and
leads to a longer lauter.
Four-roller mills
Four-roller mills have two sets of rollers. The grain first goes through
rollers with a rather wide gap, which separates the seed from the
husk without much damage to the husk, but leaves large grits. Flour
is sieved out of the cracked grain, and then the coarse grist and
husks are sent through the second set of rollers, which further crush
the grist without damaging the crusts. There are three-roller mills,
in which one of the rollers is used twice, but they are not recognized
by the German brewing industry.
Five- and Six-roller mills
Six-roller mills have three sets of rollers. The first roller crushes
the whole kernel, and its output is divided three ways: flour immediately
is sent out the mill, grits without a husk proceed to the last roller,
and husk, possibly still containing parts of the seed, go to the second
set of rollers. From the second roller flour is directly output, as
are husks and any possible seed still in them, and the husk-free grits
are channeled into the last roller. Five-roller mills are basically
six-roller mills in which one of the rollers performs double-duty.
Mashing-in
Mixing of the strike water, water used for mashing in, and milled
grist must be done in a such a way as to minimize clumping and oxygen
uptake. Traditionally this was done by first adding water to the mash
vessel, and then introducing the grist from the top of the vessel
in a thin stream. This unfortunately led to a lot of oxygen absorption,
and loss of flour dust to the surrounding air. A premasher, which
mixes the grist with mash-in temperature water while it is still in
the delivery tube, reduces oxygen uptake and prevents dust from being
lost.
Mashing in is typically done between 35 °C and 45 °C, but
for single-step infusion mashes mashing in must be done between 62
°C and 67 °C for amylases to break down the grain's starch
into sugars. The weight-to-weight ratio of strike water and grain
varies from 1:2 for dark beers in single-step infusions to 1:4 or
even 1:5, ratios more suitable for light-colored beers and decoction
mashing, where much mash water is boiled off.
Enzymatic rests
Optimal rest temperatures for major mashing enzymes Temp Enzyme Breaks
down
40 °C ß-Glucanase ß-Glucan
50 °C Protease Protein
62 °C ß-Amylase Starch
72 °C a-Amylase Starch
In step-infusion and decoction mashing, the mash is heated to different
temperatures, at which specific enzymes work optimally. The table
at right shows displays the optimal temperature for the enzymes brewers
most pay attention to, and what material those enzymes break down.
There is some contention in the brewing industry as to just what the
optimal temperature is for these enzymes, as it is often very dependent
on the pH of the mash, and its thickness. A thicker mash acts as a
buffer for the enzymes. Once a step is passed, the enzymes active
in that step are denatured, and become permanently inactive. The time
between rests is preferably as short as possible, but if the temperature
is raised more than 1 °C per minute, enzymes may be prematurely
denatured in the transition layer near heating elements.
ß-glucanase rest
ß-glucan is a chain of the beta isomer of glucose molecules,
and found mainly in the cell walls of plants, and in this context
is also known as cellulose. A ß-glucanase rest done at 40 °C
is practiced in order to break down cell walls and make starches more
available, thus raising the extraction efficiency. Should the brewer
let this rest go on too long, it is possible that a large amount of
ß-glucan will dissolve into the mash, which can lead to a stuck
mash on brew day, and cause filtration problems later in beer production.
Protease rest
Protein degradation via a protease rest plays many roles: production
of free-amino nitrogen (FAN) for yeast nutrition, freeing of small
proteins from larger proteins for foam stability in the finished product,
and reduction of haze-causing proteins for easier filtration and increased
beer clarity. In all-malt beers, the malt already provides enough
protein for good head retention, and the brewer needs to worry more
about more FAN being produced than the yeast can metabolize, leading
to off flavors. The haze causing proteins are also more prevalent
in all-malt beers, and the brewer must strike a balance between breaking
down these proteins, and limiting FAN production.
ß-amylase rest
Starch is an enormous molecule made up of branching chains of glucose
molecules. ß-amylase breaks down these chains from the end molecules
forming links of two glucose molecules, i.e. maltose. ß-amylase
cannot break down the branch points, although some help is found here
through low a-amylase activity and enzymes such as limit dextrinase.
The maltose will be the yeasts main food source during fermentation.
During this rest starches also cluster together forming visible bodies
in the mash. This clustering eases the lautering process.
a-amylase rest
The a-amylase rest is also known as the scarification rest, because
during this rest the a-amylase breaks down the starches from the inside,
and starts cutting off links of glucose one to four glucose molecules
in length. The longer glucose chains, along with the remaining branched
chains, give body and fullness to the beer.
Decoction "rests"
In decoction part of the mash is taken out of the mash tun and placed
in a cooker, where it is boiled for a predetermined amount of time.
This caramelizes some of the sugars, given the beer a deeper flavor
and color, and frees more starches from the grain, making for a more
efficient extraction from the grains. The portion drawn off for decoction
is calculated so that the next rest temperature is reached by simply
putting the boiled portion back into the mash tun. Before drawing
off for decoction, the mash is allowed to settle a bit, and the thicker
part is typically taken out for decoction, as the enzymes have dissolved
in the liquid, and the starches to be freed are in the grains, not
the liquid. This thick mash is then boiled for around 15 minutes,
and returned to the mash tun.
The mash cooker used in decoction should not be allowed to scorch
the mash, but maintaining a uniform temperature in the mash is not
a priority.
Mash-out
After the enzyme rests, the mash is raised to its mash out temperature.
This frees up about 2% more starch, and makes the mash more viscous,
allowing the lauter to process faster. It would be nice to raise the
mash to 100 °C for mash out and have a very viscous liquid, but
a-Amylase quickly denatures above 78 °C and any starches extracted
above this temperature cannot be broken down and will cause a starch
haze in the finished product, or in larger quantities an unpleasantly
harsh taste can evolve. Therefore the mash out temperature rarely
exceeds 78 °C.
If the lauter tun is a separate vessel from the mash tun, the mash
is transferred to the lauter tun at this time. If the brewery has
a combination mash-lauter tun, the agitator is stopped after mash-out
temperature is reached and the mash has mixed enough to ensure a uniform
temperature.
Lautering
Lautering is the separation of the extracts won during mashing from
the spent grain. It is achieved in either a Lauter tun, a wide vessel
with a false bottom, or a mash filter, a plate-and-frame filter designed
for this kind of separation. Lautering has two stages: first wort
run-off, during which the extract is separated in an undiluted state
from the spent grains, and sparging, in which extract which remains
with the grains is rinsed off with hot water.
Lauter tun
A lauter tun is the traditional vessel used for separation of the
extracted wort. While the basic principle of its operation has remained
the same since its first use, technological advanced have led to better
designed lauter tuns capable of quicker and more complete extraction
of the sugars from the grain.
The false bottom in a lauter tun has thin (0.7 to 1.1 mm) slits to
hold back the solids and allow liquids to pass through. The solids,
not the false bottom, form a filtration medium and hold back small
solids, allowing the otherwise cloudy mash to run out of the lauter
tun as a clear liquid. The false bottom of a lauter tun is today made
of wedge wire, which can provide a free-flow surface of up to 12%
of the bottom of the tun.
The run off tubes should be evenly distributed across the bottom,
with one tube servicing about 1 m² of area. Typically these tubes
have a wide, shallow cone around them to prevent drastic forces from
compacting the grain directly above the outlet. In the past the run-off
tubes flowed through swan-neck valves into a wort collection grant.
While visually stunning, this system led to a lot of oxygen uptake.
Such a system has mostly been replaced either by a central wort-collection
vessel or the arrangement of outlet ports into concentric zones, with
each zone having a ring-shaped collection pipe. Brewhouses in plain
public view, particularly those in brewpubs, often maintain the swan-neck
valves and grant for their visual effect.
A quality lauter tun has rotating rake arms with a central drive
unit. Depending on the size of the lauter tun, there can be between
two and six rake arms. Cutting blades hang from these arms. The blade
is usually wavy and has a plough-like foot. Each blade has its own
path around the tun and the whole rake assembly can be raised and
lowered. Attached to each of these arms is a flap which can be raised
and lowered for pushing the spend grains out of the tun. The brewer,
or better yet an automated system, can raise and lower the rake arms
depending on the turbidity (cloudiness) of the run-off, and the tightness
of the grain bed, as measured by the pressure difference between the
top and bottom of the grain bed.
There must be a system for introducing sparge water into the lauter
tun. Most systems have a ring of spray heads that insure an even and
gentle introduction of the sparge water. The watering system should
not beat down on the grain bed and form a channel.
Large breweries have self-closing inlets on the bottom of the tun
through which the mash is transferred to the lauter tun, and one outlet,
also on the bottom of the tun, into which the spent grains fall after
lautering is complete. Craft breweries often have manways on the side
of the mash tun for spent grain removal, which then must be helped
along to a large extent by the brewer.
Some small breweries use a combination mash/lauter tun, in which
the rake system cannot be implemented because the mixing mechanism
for mashing is of higher importance. The stirring blades can be used
as an ersatz rake, but typically they cannot be moved up and down,
and would disturb the bed too much were they used deep in the grain
bed.
Mash Filter
A mash filter is a plate-and-frame filter. The empty frames contain
the mash, including the spent grains, and have a capacity of around
one hectoliter. The plates contain a support structure for the filter
cloth The plates, frames, and filter cloths are arranged in a carrier
frame like so: frame, cloth, plate, cloth, with plates at each end
of the structure. Newer mash filters have bladders that can press
the liquid out of the grains between spargings. The grain does not
act like a filtration medium in a mash filter.
Boiling
Boiling the won extracts, called wort, ensures its sterility, and
thus prevents a lot of infections. During the boil, hops are added,
which contribute their bitter aromas and flavor compounds to the beer,
and, along with the heat of the boil, causes proteins in the wort
to coagulate and the pH of the wort to fall. Finally, the vapors produced
during the boil volatilize off flavors, including dimethyl sulfide
precursors.
The boil must be conducted so that is it even and intense. The boil
lasts between 60 and 120 minutes, depending on its intensity, the
hop addition schedule, and volume of wort the brewer expects to evaporate.
Boiling Equipment
The simplest boil kettles are direct-fired, with a burner underneath.
These can produce a vigorous and favorable boil, but are also apt
to scorch the wort where the flame touches the kettle, causing caramelization
and making clean up difficult.
Most breweries use a steam-fired kettle, which uses steam jackets
in the kettle to boil the wort. The steam is delivered under pressure
by an external boiler.
State-of-the-art breweries today use many interesting boiling methods,
all of which achieve a more intense boiling and a more complete realization
of the goals of boiling.
Many breweries have a boiling unit outside of the kettle, sometimes
called a calandria, through which wort is pumped. The unit is usually
a tall, thin cylinder, with many tubes upwards through it. These tubes
provide an enormous surface area on which vapor bubbles can nucleate,
and thus provides for excellent volitization. The total volume of
wort is circulated seven to twelve times an hour through this external
boiler, insuring that the wort is evenly boiled by the end of the
boil. The wort is then boiled in the kettle at atmospheric pressure,
and through careful control the inlets and outlets on the external
boiler, an overpressure can be achieve in the external boiler, raising
the boiling point a few Celsius degrees. Upon return to the boil kettle,
a vigorous vaporization occurs. The higher temperature due to increased
vaporization can reduce boil times up to 30%. External boilers were
originally designed to improve performance of kettles which did not
provide adequate boiling effect, but have since been adopted by the
industry as a sole means of boiling wort.
Modern brewhouses can also be equiped with internal calandria, which
requires no pump. It works on basically the same principle as external
units, but relies on convection to move wort through the boiler. This
can prevent overboiling, as a deflector above the boiler reduces foaming,
and also reduces evaporation. Internal calandria are generally difficult
to clean.
Energy Recovery
Boiling wort takes a lot of energy, and it is wasteful to let this
energy escape into the atmosphere. The simplest was to recover this
energy is with a kettle vapor condenser (German: Pfaduko, from the
really long word Pfannendunstkondensator). A kettle vapor condenser
is often nothing more than a plate heat exchanger.
Whirlpool
At the end of the boil, the wort is set into a whirlpool. The so-called
teacup effect forces the more dense solids (coagulated proteins, vegetable
matter from hops) into a cone in the center of the whirlpool tank.
In most large breweries, there is a separate tank for whirlpooling.
These tanks have a large diameter to encourage settling, a flat bottom,
a tangential inlet near the bottom of the whirlpool, and a outlet
on the bottom near the outer edge of the whirlpool. A whirlpool should
have no internal protrusions that might slow down the rotation of
the liquid. The bottom of the whirlpool is often slightly sloped towards
the outlet. Newer whirlpools often have "Denk rings" suspended
in the middle of the whirlpool. These rings are aligned horizontally
and have about 75% of the diameter of the whirlpool. The Denk rings
prevent the formation of secondary eddies in the whirlpool, encouraging
the formation of a cohesive trub cone in the middle of the whirlpool.
Smaller breweries often use the brewkettle as a whirlpool.
Wort Cooling
After the whirlpool, the wort must be brought down to fermentation
temperatures before yeast is added. In modern breweries this is achieved
through a plate heat exchanger. A plate heat exchanger has many ridged
plates, which form two separate paths. The wort is pumped into the
heat exchanger, and goes through every other gap between the plates.
The cooling medium, usually water, goes through the other gaps. The
ridges in the plates ensure turbulent flow. A good heat exchanger
can drop 95 °C wort to 20 °C while warming the cooling medium
from about 10 °C to 80 °C. The last few plates often use a
cooling medium which can be cooled to below the freezing point, which
allows a finer control over the wort-out temperature, and also enables
cooling to around 10 °C. After cooling, oxygen is often dissolved
into the wort to revitalize the yeast and aid its reproduction.
Fermenting
Fermentation, as a step in the brewing process, starts as soon as
yeast is added to the cooled wort. This is also the point at which
the product is first called beer. It is during this stage that sugars
won from the malt are metabolized into alcohol and carbon dioxide.
Fermentation tanks come in all sorts of forms, from enormous tanks
which can look like storage silos, to five gallon glass carboys in
a homebrewer's closet.
Most breweries today use cylindroconical vessels, or CCVs, have a
conical bottom and a cylindrical top. The cone's aperture is typically
around 60°, an angle that will allow the yeast to flow towards
the cones apex, but is not so steep as to take up too much vertical
space. CCVs can handle both fermenting and conditioning in the same
tank. At the end of fermentation, the yeast and other solids which
have fallen to the cones apex can be simply flushed out a port at
the apex.
Open fermentation vessels are also used, often for show in brewpubs,
and in Europe in wheat beer fermentation. These vessels have no tops,
which makes harvesting top fermenting yeasts very easy. The open tops
of the vessels make the risk of infection greater, but with proper
cleaning procedures and careful protocol about who enters fermentation
chambers when, the risk can be well controlled.
Fermentation tanks are typically made of stainless steel. If they
are simple cylindrical tanks with beveled ends, they are arranged
vertically, as opposed to conditioning tanks which are usually laid
out horizontally.
A very few breweries still use wooden vats for fermentation as wood
is difficult to keep clean and infection-free and must be repitched
more or less yearly.
After high kraeusen a bung device (German: Spundapparat) is often
put on the tanks to allow the CO2 produced by the yeast to naturally
carbonate the beer. This bung device can be set to a given pressure
to match the type of beer being produced. The more pressure the bung
holds back, the more carbonated the beer becomes.
Conditioning
When the sugars in the fermenting beer have been almost completely
digested, the fermentation slows down and the yeast starts to settle
to the bottom of the tank. At this stage, the beer is cooled to around
freezing, which encourages settling of the yeast, and causes proteins
to coagulate and settle out with the yeast. Unpleasant flavors such
as phenolic compounds become insoluble in the cold beer, and the beer's
flavor becomes smoother. During this time pressure is maintained on
the tanks to prevent the beer from going flat.
If the fermentation tanks have cooling jackets on them, as opposed
to the whole fermentation cellar being cooled, conditioning can take
place in the same tank as fermentation. Otherwise separate tanks (in
a separate cellar) must be employed.
Filtering
Filtering the beer stabilizes the flavor, and gives beer its polished
shine and brilliance. Not all beer is filtered. When tax determination
is required by local laws, it is typically done at this stage in a
calibrated tank.
Filters come in many types. Many use pre-made filtration media such
as sheets or candles, while others use a fine powder made of, for
example, diatomaceous earth, also called kieselguhr, which is introduced
into the beer and recirculated past screens to form a filtration bed.
Filters range from rough filters that remove much of the yeast and
any solids (e.g. hops, grain particles) left in the beer, to filters
tight enough to strain color and body from the beer. Normally used
filtration ratings are divided into rough, fine and sterile. Rough
filtration leaves some cloudiness in the beer, but it is noticeably
clearer than unfiltered beer. Fine filtration gives a glass of beer
that you could read a newspaper through, with no noticeable cloudiness.
Finally, as its name implies, sterile filtration is fine enough that
almost all microorganisms in the beer are removed during the filtration
process.
Sheet (Pad) Filters
These filters use pre-made media and are relatively straightforward.
The sheets are manufactured to allow only particles smaller than a
given size through, and the brewer is free to choose how finely to
filter the beer. The sheets are placed into the filtering frame, sterilized
(with hot water, for example) and then used to filter the beer. The
sheets can be flushed if the filter becomes blocked, and usually the
sheets are disposable and are replaced between filtration sessions.
Often the sheets contain powdered filtration media to aid in filtration.
It should be kept in mind that pre-made filters have two sides. One
with loose holes, and the other with tight holes. Flow goes from the
side with loose holes to the side with the tight holes, with the intent
that large particles get stuck in the large holes while leaving enough
room around the particles and filter medium for smaller particles
to go through and get stuck in tighter holes.
Sheets are sold in nominal ratings, and typically 90% of particles
larger than the nominal rating are caught by the sheet.
Kieselguhr Filters
Filters that use a powder medium are considerably more complicated
to operate, but can filter much more beer before needing to be regenerated.
Common media include diatomaceous earth, or kieselguhr, and perlite.
Packaging
Packaging is putting the beer into the containers in which it will
leave the brewery. Typically this means in bottles and kegs, but it
might include bulk tanks for high-volume customers.
Craft Brewing
Before Prohibition in the United States, breweries were local institutions,
with a few exceptions. The costs involved in moving large quantities
of beer while maintaining its quality necessitated that beer be made
near where it was to be consumed. Prohibition, as could be expected,
closed most of the breweries in the United States, and the few that
were able to remain open by producing near beer, malt extract, yeast,
and other beer-related products, were in an advantageous position
to produce and sell beer after Prohibition was lifted. During Prohibition,
the advancements in refrigeration and motorvehicles made large regional
and national breweries possible. These remaining breweries quickly
became large enough to be household names all over the nation, and
concentrated mostly on the style with the broadest appeal: American
light lagers. Local breweries, with their niche beers, were lost in
America.
In 1978, Jimmy Carter signed into law a bill explicitly allowing
people to brew beer for private consumption. As the homebrewing movement
grew, homebrewers looked to re-create beers they had enjoyed in places
with a more varied beer assortment. The rise of imported beers and
homebrewing brought a demand for more beer styles, and locally brewed
beer. Answering this need, smaller breweries started popping up across
America, and a whole industry grew around the microbrewing industry.
Craft brewing takes different forms in different countries. In America,
where the infrastructure needed to be reinvented, and many brewers
came from the homebrewing world, where items are adapted to use in
brewing, breweries take many different forms, and are often made from
adapted equipment. European craft breweries, which did not experience
prohibition and have a deep cultural tradition in many areas, are
often smaller versions of large breweries, and are equipped with all
the bells and whistles as large breweries, such as automation and
computer control of the lautering process.
The number of craft brewers in the United States has been slowly
declining in the last decade, while craft brewers have made up a larger
percentage of beer sales in America, likely reflecting a more discriminating
customer, who is less tolerant of off flavors and poorly made beers.
References
http://www.answers.com/topic/brewery
ISBN 3921690390: Technology Brewing and Malting, Wolfgang Kunze, 2nd
revised edtion, VLB Berlin. Available at their
website
http://www.beertown.org/craftbrewing/statistics.html:
Craft Brewery definitions at the bottom of the page
© 2006 Palmetto State Brewers, Inc.
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