Viva La Fungi - Philly Beer Scene Magazine
By Jimmy McMillan

When most
people discuss beer, they speak of its flavor, color, hop aroma,
alcohol content, and style in which it was brewed but rarely do they
ever discuss one
of the most critical ingredients of beer. This
ingredient is arguably the most important of all the ingredients that
make up our beloved beverage, and can be directly linked to our
survival throughout the ages. This special ingredient shall be forever
named yeast!
Yeast is the workhorse of all beer, but is often overlooked or ignored
when one talks about and rates beers. There is an old saying, “Brewers
make wort, yeast makes beer,” and without yeast, beer as we know it
wouldn’t exist. Instead, we would be drinking on an overly-sweet and
unpleasantly bitter beverage that would not give us the euphoric buzzed
feeling we’re accustomed to. In this article, we attempt to simplify
the complexity of yeast: how they work, the differences yeast can
create in beers and how various regions produce different yeast
samples, thus making the styles of beer that we all know and love.
The standard dictionary definition of yeast is “any of various small,
single-celled fungi of the phylum Ascomycota that reproduce by fission
or budding, the daughter
cells often remaining attached, and they
are capable of fermenting carbohydrates into alcohol and carbon
dioxide.” To put it more simply, yeast is a single-celled fungus that
eats simple sugars to produce alcohol and carbon dioxide. The
scientific name for brewer’s yeast is Saccharomyces, which comes from
the Greek word “Saccharo,” meaning sugar and myces (mushroom or
fungus). Yeast plays the beginning role of decomposition in nature and
is literally found everywhere, living on the skins of fruits and
vegetables, hibernating inside the bellies of bees, and even living on
our skin.
Why does
yeast aid in the production of tasty beverages such as beer? Before we
can discuss yeast’s role in beer, we must first understand what beer is
prior to adding yeast, or what brewers call “wort.” Let’s briefly go
over how beer is made all around the world. The main ingredient is
usually malted barley, which are barley seeds that have been allowed to
sprout. Once sprouted, the barley is then heated to stop the
germination process, which preserves the complex carbohydrates, or
starches, that would have been used if the seeds were to grow into
mature plants. These carbohydrates are the beginning of what will become
food for the yeast; because they’re too complex for standard brewer’s
yeast at this stage, they are converted into simpler sugars through a
process called mashing. This is when the barley is soaked in water at a
specific temperature for a set amount of time. During the mashing
process, natural enzymes in the grain start to break down the
carbohydrates into smaller chain carbohydrates, or what we would refer
to as simple sugars. We measure the density of these sugars in the water
by specific gravity, or in degrees Plato, for use in calculating the
ABV (Alcohol by Volume) in the final product. The wort is now boiled and
the recipe is followed as planned with various hop and/or spice
additions. After boiling, the wort is cooled to a precise
temperature–usually around 70° Fahrenheit–and placed into fermentation
vessels where it’s inoculated with yeast cells. Within 12-24 hours there
should be considerable evidence that the yeast are doing their job, or
fermenting: an excessive amount of CO2
gas being released from the fermenter and a krausen (thick yellow/beige foam) on top.
Alcohol and CO2 are the main by-products of yeast fermentation. Most
of us know what the alcohol does, and is one of the main reasons we
enjoy drinking beer, but
CO2 is usually an afterthought. The
majority of the breweries today allow fermentation to release the CO2
into the environment, and when it’s time to carbonate the beer, they
purchase commercial CO2 and force it into the beer. Without CO2, beer
would be a “still” beverage much like wine, and not have the bubbles
and the frothy head that we enjoy. Before we were able to capture and
pressurize CO2 into large steel tanks, there were only “cask
conditioned” and “bottle conditioned” beers available, which are
naturally carbonated by the yeast. This style of beer is becoming more
and more popular today and is created a number of ways. The main way
breweries today are naturally carbonating beers is by allowing
fermentation to finish and then adding a precise amount of some type of
sugar before it goes into its bottle or cask. This slowly starts
fermentation up again, and the yeast start producing a small amount of
CO2 and alcohol, just enough to carbonate a beer.
There are currently about 1,500 different yeast strains, but most
brewers usually select from a small number of good, known strains that
have been passed down for hundreds of years. The three easiest ways to
categorize yeast are by ale yeast (Saccharomyces cerevisiae), lager
yeast (Saccharomyces pastorianus) and wild yeast (Brettanomyces). Top
fermenting ale yeast work best in our average comfort temperatures,
65°-75° Fahrenheit, create more fruity aroma and flavors (phenols and
esters) and can take an average of ten days to complete fermentation. A
lot of the new craft beers around today use ale yeast–IPA’s,
hefeweizens, American pale ales, porters, stouts, and even kölsch.
Bottom fermenting lager yeast prefers cooler fermenting temperatures,
between 48°-58° Fahrenheit, and produces a more “clean” flavored beer,
but can take up to forty-five days to complete fermentation. This is the
yeast strain that has been favored over the years and is used to make
most of
the larger commercial beers, such as lagers and pilsners.
Wild yeast isn’t new to the brewing industry. It has always been a part
of lambic production, as well as some of the funkier saison or
farmhouse style beers. It wasn’t until the early 1900s, however, when
Brettanomyces was identified as cause of spoilage in English ales, and
thusly named “British fungus.” Brettanomyces, called Brett for short,
is a form of yeast that is acidogenic and, when allowed to grow over
time, creates acetic acid; this is the same acid that makes vinegar so
tart. Recently, American breweries like Russian River, Lost Abbey,
Jolly Pumpkin, Allagash, Cascade and many others have been welcoming
this yeast into their brews, producing a complex character that can
only be obtained by the use of Brett, other bacterial strains and usual
long aging. Little is still known about the various strains of wild
yeast and their actual reactions during fermentation, but the recent
interest in sour beers is striking up significant scientific research.
Once the type of beer to be brewed is determined and the yeast strain
has been selected, a specific amount of yeast needs to be “pitched,”
which is referred to as the “cell count.” Wyeast, a large manufacturer
of brewer’s yeast, claim that, “A good rule to follow is a million cells
per milliliter per degree Plato.” This means that you need 20 million
cells per ml for a 20 degree Plato (1.080 specific gravity) beer, or
about 9.5 billion cells per pint for a 7% beer. That’s more than the
total population of the earth for a single pint of beer. Once the yeast
has been pitched, the lag phase begins. This phase occurs during the
first twelve hours and mainly consists of the cells absorbing the
oxygen, minerals and various amino acids which will help them process
the sugars and bud (replicate) daughter cells during the main
fermentation. After the lag phase, the yeast starts budding
exponentially and begins processing the various sugars in the wort.
There are a number of different carbohydrates in the wort, consisting of
glucose, fructose, sucrose, but mainly maltose. The yeast cannot fully
consume some of the more complex sugars such as maltotriose, which
gives the beer a sweet and malty flavor.
As we near the end of fermentation, the yeast shuts down, clumps
together and falls to the bottom of the fermentation vessel. This
process, called flocculation, is unique to brewer’s yeast. Chris White,
from White Labs explains, “The ability to flocculate is a product of
natural selection. Brewers have continually collected yeast either from
the bottom or top of a fermenter and in doing so, selected for
increasingly flocculent strains.” The reason for this flocculation is to
help clarify the beer. If the yeast is less flocculent, like in a
hefeweizen, they stay in suspension and yield a cloudy and hazy beer.
Wild yeast, such as Brettanomyces, do not flocculate well; this is why
some of the newer style “wild ales” are recommended to age like a bottle
of wine.
The rate
at which the yeast eats the malt sugars is called “apparent
attenuation,” which is measured by the percentage of sugars the yeast
consumes. White Labs, one of the nation’s main yeast providers, says
their California ale yeast strain is said to have a 73-80% attenuation,
which means the yeast should consume 73-80% of the sugars in the wort.
The higher the attenuation percentage, the less residual sweetness and
body the finished beer will have. After fermentation is complete, the
specific gravity, or Plato, is taken again, calculated with the original
gravity, and the attenuation is measured along with the ABV. For
professional breweries, if the attenuation of the yeast is not precise,
then the final product will never be consistent and will fail at the
quality control department. Yeast is very particular to the region in
which they come from. If you have ever visited San Francisco and had the
sourdough bread, you will know that it is unlike anywhere else in the
US. This is due to the types of wild yeast and bacteria that are native
within that region and the by-products they produce during
fermentation. The exact same concept goes for beer.
Up until recent laboratory technology, breweries would use the same
mature yeast strain time and time again, and it was considered their
“house” yeast strain. This is what gives some of the older brew houses
in Europe such a unique smell and flavor. Now with modern
transportation, we can safely ship yeast samples from all around the
world without worry of excess heat, time, or contamination of some other
yeast or bacterial strain. Today, Belgian style beers that are made in
America are mostly using yeast strains that have been brought over
from Belgian many years ago.
These regional differences inhibit many different styles of flavors
and aromas in the beer. These flavors and aromas are referred to as
phenols and esters. Consider the difference between American pale ale
and a German hefeweizen: these are found more in the esters produced by
the yeast than in the wheat added in the hefeweizen. Hefeweizen,
literally meaning “yeast wheat,” has a slight banana or clove essence
that’s caused by the ester, Isoamyl acetate. Hefeweizens are fermented
at the warmer end of ale temperatures and use low flocculating yeast
from Germany to produce these robustly-flavored esters. Most American
pale ales are fermented at a slightly lower temperature and use
cleaner-flavored and more flocculent yeast from California. Another
common flavor found in some English and Belgian Style ales that are
strictly due to yeast are green apple/pear ester, or Isoamyl butyrate.
The human tongue is very sensitive to these flavors, which means they
can be very unpleasant at higher concentrations. Wild yeast, or
Brettanomyces, is sometimes blamed for ‘solvent’-like flavors in beer,
but these can come from commercial yeast strains as well.
Besides the production of Ethel alcohols, yeast is the microscopic
fungus responsible for providing the bubbles, the alcohol and many of
the aromas and flavors in beer. In this light, yeast can easily be
argued as being the most critical component of making beer. Many
breweries keep their yeast strains under lock and key with high levels
of security, while others simply use the wild yeast that just happens to
be floating in the air around their region. Without these
single-celled organisms, there would be no beer, wine, cider, mead,
hard spirits, bread, doughnuts, or even pizza to enjoy. It is time to
give the hard working yeast cells the attention and respect that they
deserve. The next time you sit down to enjoy your favorite craft beer
and criticize its flavors and aromas, don’t forget it’s not just about
the hops and malt. Trillions upon trillions of microorganisms created
that oh so tasty beverage.