Laisy Almanza
Pre-Med Student at USFSP
Due: July 25th, 2014
Even though beer was brewed from the earliest colonialtimes the lager style of beer was widely introduced by German immigrants and due to the lighter color and flavor profile became the dominant American choice by the mid 19th century and for this reason most people believe that beer started in Germany
Malted barley is a naturally
processed form of barley, which is a grain similar to wheat in appearance. A “maltster”
will steep the barley in water until it begins to sprout under certain
conditions. The germinated barley is then dried and once the drying is complete
the barley is officially malted. During this procedure, sugars, soluble
starches and characteristics in the barley desirable for brewing beer are
developed. The malt is mostly converted to sugars through a process called
mashing where the malt is submerged in water at precise temperatures that allow
enzymes in the barley to convert starches to sugars. These sugars are converted
to alcohol, carbon dioxide and the flavor of beer through fermentation as
stated before. The liquid extracted from the mashing process is known as wort.
Some brewers choose to substitute corn, rice, wheat, rye, or other grains for a
portion of the malt because although the fermentable sugars created from the
starches of these grains will ferment through the same process as the malt
sugars do, they will add their individual fermented character to the beer. This
is used mostly to lighten the taste of the beer (Briggs, 1971) .
For home brewers there are malt
extracts available so that they do not have to go through the process of
malting the barley or even mashing the grains. The malt extract is malted
barley that has been processed into a sweet malt soup. Then, depending on if
the brewer wants moist or dry malt, 70-80 percent of the water is evaporated to
give a concentrated syrup or all of the water is evaporated to give a dry
powder. There are also many malt extracts and home-brew kits that have
different hop flavors so that the home brewer can add that floral taste unique
to hops just as breweries do to their beer. All that would need to be done by
the home brewer is to add water and yeast, which is sometimes also provided in
the kits (Papazian, 2003) .
As hops are considered primarily
as a flavour ingredient for beer, with the added benefit of having
anti-microbial effects, hop research is focused on hops as a bittering agent,
as an aroma contributor and as a preservative (Schönberger & Kostelecky, 2011) . Hops have been used
in making beer for approximately 200 years (Filmer, 1982) . It is important to remember that hops
are conelike flowers of the hop vine and because of this add a floral aroma
along with their bitterness. Unfortunately, because of this same reason they
are perishable (Lewis & Young, 1995) . The sweetness of
malts is balanced by the hop’s bitterness. Hops can also extend the life of the
beer and can improve head retention, which is why brewers consider hops
extremely important. It is important to understand the biochemistry of hops and
how it can interact with the beer making process. Hop's produce Lupulin glands,
which are tiny capsules containing resins and oils that become the major
contributing factors through the brewing process. The hop oils provide the
floral flavor and smell while the resins add to the bitterness of the beer. Hop
oils should be used scarcely and can be added at many stages of the brewing
process either at the end of boiling, during or after fermentation or even just
before packaging (Lewis & Young, 1995) .
Even though it may seem unimportant,
the water you use for making beer is also very important especially for home
brewers because it will add its character to the beer as well. It is important
to make sure that the water tastes good and that it does not contain any excess
chemicals or minerals because they will change the taste of the beer. It is
also important to use potable water in breweries so that the microbial growth
can be minimal.
In my opinion the most important
ingredient in the brewing process is the yeast. Yeast is responsible for
converting the bittersweet “tea” made from the fermentable sugars and the hops
to the alcoholic beverage known as beer. Yeasts are living microorganisms that
use sugar as food for their life cycle. Yeast can grow aerobically
(respiration) or anaerobically (fermentation) but only the anaerobic process is
used in beer production. Unfortunately, even though there are thousands of
unique yeasts in the world, most of them are wild yeasts, which will result in
the production of some very unique brews that aren’t always very delightful to
taste. Wild yeasts not only cause odd savors but also overflowing, over
carbonation, haze development and all kinds of indescribable fermentation
features. In general there are two types of yeast used in brewing. These are lager
yeast and ale yeast. Lager yeasts ferment at cooler temperatures and generally
yield a much cleaner tasting beer with fewer esters while ale yeasts tend to
yield a beer with fruitier esters. There is much more diversity among ale
yeasts than lager yeasts. Ale yeasts (Saccharomyces
cerevisiae) are said to be “top-fermenters” because during the beginning of
fermentation period they tend to flocculate on the surface of the beer while
lager yeasts (Saccharomyces
carlsbergensis) are said to be “bottom-fermenters” because they flocculate
and sediment at the bottom of the tank. Both of the yeasts are broken down
again into groups of strains (Papazian, 2003) .
The cooled wort obtained from
mashing of the malted barley is fermented by yeast to make an immature beer
also known as green beer. The main fermentation, in which this green beer along
with the yeast is produced, is followed by a slower process at a lower
temperature and with less yeast also known as secondary fermentation or maturation.
Secondary fermentation is the process of keeping green beer in contact with
yeast after the primary fermentation has ended. For the yeast to live and grow
successfully the wort must contain sufficient amount of nutrients. Yeasts need
very specific conditions and nutrients to be able to flourish as needed to for
the brewing process. For example, they need fermentable carbohydrates,
assimilable nitrogen, molecular oxygen, biotin, sources of phosphorus and
sulfur, calcium and magnesium ions and trace elements such as copper and zinc
ions. Some worts can be enhanced by adding certain trace elements or other
nutrients needed for the yeast to grow successfully. Another important
parameter for the wort is the dissolved oxygen content because the molecular
oxygen requirement is different for certain yeasts. Enough molecular oxygen has
to be supplied at the beginning of fermentation but once this is done then no
more is needed and anaerobic conditions are established and essential to
prevent detrimental oxidation reactions that can spoil the beer. The quantity
of oxygen is inversely proportional to the specific gravity as well as the
temperature. Too much oxygen results in too vigorous fermentation and excessive
yeast growth and too little cause accelerated loss in yeast vitality and
viability. Even on wort, yeast must be
induced to produce the maximum amount of alcohol and have the minimum amount of
growth. This is done by restricting the availability of oxygen and using lower
fermentation temperature than those preferred by the organism.
As stated earlier secondary
fermentation involves keeping the green beer in contact with the yeast after
primary fermentation in ended. An advantage of doing this is that any oxygen which
gains access will be absorbed instantaneously by the microbe. Once the yeast is
removed then the brewer must be careful and make sure that oxygen does not
enter and touch the product. Maturation most often involves the gradual
lowering of the temperature and giving enough time so that the yeast can settle
out or flocculate and chill haze particles can form. This waiting period is
called lagering or aging as mentioned earlier. This process can be expansive
and many brewers rather accelerate this process. Brewers can accelerate the formation, prevent
the formation, or accelerate the removal of the chill haze that usually forms
during maturation. The formation of these particles is
catalyzed by molecular oxygen and controlling it can help accelerate its
formation or simply stop its production.
Once pitched into wort, yeast
uses the nutrients in the wort to provide energy (ATP) and in the process
produces alcohol and carbon dioxide. This process also produces reducing power
(NADPH) for the synthesis of new yeast substance. The nutrients can also be
directly assimilated into new cell components or used to generate intermediates
for this process. In addition, these energies lead to the synthesis and
secretion into the work of a large number of minor metabolic products, which
can add special features savors and scents (Lewis & Young, 1995) .
The production of beer includes not
only fermentation but glycolysis as well. It is extremely important to
understand all biochemical pathways involved in brewing so that the complexity
of the beer making process can be appreciated. First of all a biochemical
pathway is recognized as a serious of reactions, each mediated by an enzyme in
which the product of one reaction becomes the substrate of the next. Pathways
whose purpose is to make energy chemically oxidize their substrates normally
achieved by transferring a hydride ion to an enzyme cofactor. This oxidized
cofactor NAD+ is converted to NADH (reduced form). Dehydrogenase enzymes
conduct the oxidation-reduction reactions. Because energy is released through
oxidation, the reaction is controlled so that some of the energy released is held
by the cell in the form of ATP (adenosine triphosphate).
ADP + inorganic
phosphate (Pi ) à
ATP
The
reaction above consumes energy and is driven by high-energy compounds formed
during metabolism and the inverse reaction (hydrolysis of ATP) releases energy
which can be used to synthesize new products. The source of the heat rising
during fermentation of the wort comes from the fact that energy transfer
reactions are never 100% effective and waste energy is always dispersed.
Usually sufficient waste heat is formed to increase the temperature of a lagged
vessel about 17°C and this heat must be removed by cooling. Glycolysis (figure
1), which is an important pathway in the brewing process, is said to be
amphibolic. This means that it can have both catabolic and anabolic functions.
Figure 1. Simplified Process of Glycolysis
The fermentable sugars in
brewer’s wort are maltose, maltotriose and smaller amounts of sucrose glucose
and fructose. The trisaccharides are transported into the cell and hydrolyzed
to glucose while sucrose is hydrolyzed outside the cell to glucose and fructose
then transported into the cell. The
enzyme invertase is located in the outer layers of the cell wall however some leaks
into the beer but fortunately is quickly deactivated by heat. The glucose
located inside the cell is phosphorylated using ATP by the enzyme hexokinase to
yield glucose 6-phosphate while fructose is phosphorylated to yield fructose
6-phosphate because subsequent enzymes recognize only phosphorylated compounds.
The metabolism of glucose proceeds by the glycolytic pathway that contains 10
enzymes that oxidize the six-carbon sugar to two molecules of pyruvate and
through this process two molecules of ATP and two of NADH are gained (Lewis & Young, 1995) .
The job of a brewer is to combine
all of the ingredients discussed and pursue fermentation, which lasts 10 days
to several months depending of the beer style. During this time the yeast will
reproduce and disperse throughout the fermenting beer while converting sugars
to carbon dioxide, alcohols, a variety of flavors. The yeast will have run
through its supply of sugar and will began to settle at the bottom of tank, or
other fermentation vessel, after the initial 5 to 14 days. Most brewers will
transfer the clear beer top layer to a different tank and once the fermentation
process is over the beer is packaged in the designated bottle, can, or keg.
Some breweries choose to filter the beer for preservation purposes as well as
some economic reasons but some breweries prefer to not do so because it may
take some of its special character away along with the things being filtered
out.
The fermentation temperature and
quality of the yeast will determine how long the beer should be aged or if it
should be done at all. Beer made with Ale yeast and with a fermentation
temperature above 65 degrees Fahrenheit will be ready for bottling in about 2
weeks more or less. If the beer is made with very high quality lager yeast and
a fermentation temperature below 45 degrees Fahrenheit, then aging can be
advantages (Papazian, 2003) .
One of the most important things
to avoid during the brewing process is the growth of unwanted organisms. The
science of microbiology involves the study of organisms less than 1 mm in size.
Prokaryotes, which have no nucleus, as well as eukaryotes, which do have a
nucleus, are both important in the brewing process but for very different
reasons. Prokaryotes are the main concern when beer spoilage occurs. On the
other hand eukaryotes are divided into lower and higher eukaryotes and the
lower group includes the brewing yeast, wild yeast, and other fungi or molds.
Unfortunately microorganisms are found anywhere if the right nutrients and
other conditions are present even in air. For example, acid-tolerant bacteria
are capable of surviving in beer because they can grow in the absence of oxygen
and given the right nutrients will grow perfectly in an acidic anaerobic
environment. It is very important to make sure that the brewer does not provide
the right environment for these organisms to grow because they may be
detrimental to the beer and the person who drinks it. The brewer’s job is to
monitor their equipment and product for the appearance of any unwelcome microbes.
This can be very difficult because microbes survive best in places where water
is abundant and water, malt and cereals, sugars and hops all provide a good
environment for microbes to flourish.
Microbes found in brewing are
usually gram positive, gram negative, or simply wild yeast. The most important
members of the gram-positive group are lactic acid bacteria, Leuconostoc, streptococcus, micrococcus, and Bacillus. The ones that have become the
greatest concern to brewers are the lactic acid bacteria specifically Lactobacillus and Pediococcus because they are found most often and can spoil the
beer by making it more sour, turbid and producing diacetyl which gives an
unwanted smell and flavor. Pediococcus is encountered more often
than Lactobacillus but fortunately
they can both be isolated using the same type of media.
The gram-negative bacteria
include Enterobacteriaceae, acetic acid bacteria, Zymomonas, Pectinatus, and Megasphaera.
Enterobacteriaceae for example, which is a bacteria encountered if poor
cleaning methods are used, can spoil the beer by affecting the wort and growing
quickly producing dimethyl sulfide and diacetyl. If they affect the beer during
the beginning stages of fermentation they can produce an unwanted taste in the
beer or even decrease the growth of the yeast (Lewis & Young, 1995) .
Like stated earlier, wild yeasts
can give an undesirable taste and aroma to the beer. Any yeast that is not
considered a brewing strain is said to be a wild yeast. Unfortunately wild
yeasts can become a huge problem specifically cause they are extremely hard to
detect and are not as easily removed. They can really change the taste of the
beer if they affect the beer in early stages as well as make it cloudier in
appearance.
During the brewing process it is
important to take certain readings and make specific observation such as temperature,
specific gravity, pH, cell count, etc. A hydrometer is an instrument used to
measure the density of a liquid relative to the density of water. This is also
known as the specific gravity. Because the density of water was determined to
be 1.000, it is known that the density of the beer will be higher because of all
of the components added to the water. In result the specific gravity will also
rise to about 1.035 to 1.042. Once the yeast begins to ferment the dissolved
sugars into alcohol and carbon dioxide, the density will begin to decrease
because of the reduction in sugar content and also because alcohol is less
dense than water. A digital gravity meter can also be used to measure the
specific gravity of samples taken from tanks in the laboratory setting.
The common media used to
determine what organisms are growing in the beer are Mac Conkey agar used to
detect coliforms, Plate count agar/PCA used to detect all forms of bacteria,
Walerstein nutrient medium/WLN used to detect all forms of bacteria, Schwarz differential
medium used to detect only wild yeast, Lysine medium used to detect only wild
yeast, and Raka Ray medium which is an anaerobic medium (LinkedIn, 2014) . Other media used include LWYM (Lin's Wild
Yeast Medium)
used to detect saccharomyces wild yeast, LCSM (Lin's Cupric Sulfate Medium) used to detect non-saccharomyces
wild yeast, HLP (Hsu's Lactobacillus/Pediococcus
Medium) used to detect the growth of Lactobacillus
and Pediococcus and WLD media used to
detect all bacteria and wild yeast while impeding the growth of brewer’s yeast.
To plate the beer samples on each of the media the membrane filtration method
or the spread plate method can be used and then they are either incubated
aerobically or anaerobically. Finding Saccharomyces
species is very important because 3 of 11 killer yeasts are displayed
within the Saccharomyces genus. These killer yeasts produce toxins
that are lethal to other yeast strains and they are immune to toxins themselves
(Hammond & Eckersley, 1984) .
Some of the tests and
measurements commonly used in the laboratory setting for quality assurance are
the international bitterness unit (IBU) test, pH test, gravity test measured in
degrees Plato (density of beer wort in terms of percentage of extract by
weight), cell counts/viability, and standard reference method (SRM) test. The
IBU test simply measures the bitterness of the beer, which is usually caused by
the hops added. The pH of the beer usually starts to increase when the beer is
almost ready because of this it is important to measure the pH everyday until
it is constant or begins to increase. The original gravity is the gravity of
the sample before yeast is added and the final gravity is that which is
measured when the beer has finished fermenting.
The original gravity of wort is important because it has been shown that
as it increases the ethanol concentration of the beer coming out increases as
well (Dragone, Mussatto, & Almeida e Silva, 2007) . This can produce
unbalanced flavor in the beer, which can be undesirable. The gravity will
decrease as the beer finishes off because the yeast will have fermented most if
not all of the fermentable sugar to alcohol, which is less dense than water. The
SRM test is used specify beer color by measuring the attenuation of
light at a particular wavelength (430 nm) when passing through 1 cm
of the beer and is done by using a spectrophotometer. The
purpose of taking cell counts is to determine the concentration of cells per mL
of beer and the viability simply shows how effective or viable the yeast in
that sample is. The cell count should decrease towards the end of the brewing
process and the viability should always be close to or at exactly 100% although
it might be slightly lower when the yeast is first pitched in. If the viability
is low than there is definitely something wrong and this should be checked
immediately. Checking for all of these measurements is extremely important so
that the beer is at its best quality possible and no money is lost by having to
dispose of an entire tank of beer simply because quality control was not
adequate.
All in all it is extremely
important to follow all quality assurance protocol so that large quantities of
beer are not lost by contamination or any other reasons. Microbes are
everywhere and avoiding their contact with the beer is vital. Knowing ways to
detect or prevent contamination is one of the most significant attributes of
any brewery or homebrewer. Understanding
the importance of all the ingredients included in the brewing process from the
malt to the hops and even the type of yeast and water used is very pertinent in
beer making because only through this comprehension will you understand why
they are added at a certain stage of the process and not others. Each and every
ingredient provides some character to the beer and all of them together in the
right amounts will make the perfect beer. Whether someone is brewing at home or
for a large Brewery this paper can help understand the basics of the beer
making process
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