What follows is a guest post by none other than our very own Cheddarman. If you've ever wondered how bourbon is made... and what makes it taste the way it does... well... here's is your PhD level dissertation on the matter. Fair warning... if you hate chemistry this is going to make your head explode. If you like chemistry... you'll love it.
Now... if I can only get him to explain, in scientific terms, why scotch sucks...
and its development: some artisanal and industrial considerations
In honor of Nate
and his friends and blog followers, Rebels, Copperheads and Yankees,
and even any anonymous Ohio State University sports fans or dedicated
pink Hello Kitty Glock users that hang out at the ATF blog, I have
put together a little “review” of bourbon flavor formation.
Specifically, I will cover a number of the factors involved in the
development of bourbon flavor, beginning with the raw ingredients,
and following the process through to the end. I have not been able to
find any published scientific articles on the science and craft of
making Bourbon. However, I have a 20+ year career as a practitioner
of flavor chemistry, and can draw on my experience in that area that
includes extensive reading of the scientific literature as well as
working on a number of flavor related projects in industrial and
academic settings. Finally, for what it is worth, I could be
considered a world class expert in the flavor of chemistry of ripened
cheeses, and this gives me some unique insight into the development
of bourbon flavor. All these credentials and 50$ will get me a good
bottle of bourbon (it never got me anything else, nudge nudge, wink
wink). There are also a number of excellent sites on the world wide
web devoted to making bourbon from an artisanal approach that were
helpful in putting this review together. I hope you enjoy it. If you
want to better understand Bourbon, here is your chance to dig deep.
versus “Industrial” Bourbon
As one looks at
the types of bourbon available on the market, there appears to be 2
separate schools of thought in how to make it, clever marketing
tactics aside. One is the artisanal school (I use that term because
these distillers are practicing an art), where bourbon is made the
old fashioned way, in small batches, using pre-industrial techniques.
Whereas artisanal producers specialize in making more expensive, more
intensely flavored, or more “interesting” bourbons, the
“industrial” bourbon makeruses modern methods of production to
make a more affordable product that is generally more consistent from
batch to batch, and has a wider over all appeal due to its relatively
milder flavor profile. We will cover aspects of both approaches
One way to make
bad bourbon is to start with low quality ingredients. High quality
water is very important to bourbon. Traditionally, water from
limestone springs is used to make the malted barley and the mash.
Some writes have said that the calcium dissolved in the water somehow
contributes to high quality bourbon flavor. I doubt that is true, for
a couple of reasons: 1) Calcium carbonate from limestone filtered
water has little if any flavor. 2) The fermentation micro-organisms
need some calcium for growth, but they can obtain it from the grains.
There a number of reasons why the use of limestone filtered water was
a common historical practice. This water is filtered by slow passage
through limestone, and is generally free of off-flavors, chlorine and
iron. This is very important, as iron or chlorine in the water can
cause the formation of off some very potent undesirable flavors. Iron
will help oxidize oils present in the grains, and causes a variety of
“green” off flavors, like including freshly cut grass, metallic
flavors (imagine a penny on your tongue), drying oil based paint, and
fishy. Chlorine can react with phenols that are produced during
barley malting, the sour mash fermentation or charring of barrels.
These chloro-phenols have very potent “saltwater fishy” aromas.
They can ruin otherwise good bourbon. Enough said. The industrial
producer uses a number of steps to clean up their brewing water.
These may include ion exchange resins to remove iron and other
mineral,, as well as sand filters, activated carbon, UV light and
Ozone to remove all traces of taste or aroma from the water. As a
result, the industrial distiller can have water of even higher
quality than that coming out of a natural limestone formation.
Grains, Malt and
By U.S. law,
Bourbon must contain at least 51% corn as well as barley, rye and
wheat. The primary purpose of the grain is to provide glucose for the
yeasts to ferment into alcohol. The grains should be high in starch,
and low in vegetable oils. The oil can be a source of “oxidized
fat” off flavors. The grains are ground to improve the conversion
of starch into glucose and other sugars. If the grains get too hot
during milling, it will damage the starch and protein, and they can’t
be broken down by enzymes. Also, high amounts of heat building up in
the grains during milling can oxidize the vegetable oil.
distiller generally uses malted barley. In the malting process, dry
barley is soaked in water to activate enzymes in the grain. Wild
yeasts and lactic acid bacteria grow on the surface of the grains
during the malting process. The slow drying of the malt “hardens”
these micro-organisms, so they can survive the mash boiling step and
ferment the mash. These “wild” micro-organisms can be a source of
the batch to batch flavor variation seen with artisanal distilled
activated by the malting process are needed to break down starches
and proteins in the other grains. Without these enzymes being active
in the mash, the fermentation process would be slow and difficult to
control. Glucose and other sugars are produced from the breakdown of
starches by a set of enzymes called amylases; proteins are broken
down into amino acids by protease enzymes. The activity of these
enzymes on starch and protein helps set the stage for rapid growth of
yeast and lactic acid bacteria during the sour mash fermentation.
Glucose and amino acids are also a converted into flavor compounds by
the yeast and lactic acid bacteria.
producer may choose not to use malted barley, and instead use a
commercial mixture of “microbial” amylase and protease enzymes
produced by food grade bacteria or fungi. It is faster and cheaper
than using malted barley, and can help keep “wild” yeast and
lactic acid bacteria out of your mash fermentation.
different amounts of the 4 grains, one can change some of the flavor
profile of the bourbon. Each grain has some unique flavor components
that can be released during the fermentation. Wheat, as an example,
is supposed to have a mellowing effect upon the bourbon. Consider the
differences in flavor between a sour dough wheat, rye barley, or corn
bread; these differences in flavors can be partly attributed to the
interaction of the yeasts and bacteria with the individual grains.
The yeasts and lactic acid bacteria have special enzymes that will
release specific classes of flavor compounds from the grains. The
different grains will have varying levels of these flavor compounds.
These flavor compounds are often attached to a sugar molecule or
other non-volatile molecule; by the cutting the chemical bond, the
glucose can be harvested, and the flavor molecule is released into
The mixture of
grains and water is called mash. The mash is heated to help dissolve
the starch and protein in the grains. This also has the effect of
killing off some of the wild yeast and other bacteria that could be
present on the grains. If we use microbial enzymes instead of malted
barley, we can cook the mash at higher temperatures for a longer
time. This will, again, kill off more wild microorganisms naturally
present on the grains, and help us have a more consistent product
over time. The microbial enzymes are more heat stable that the
enzymes from malted barley and are active at relatively high
temperatures, and can be added when the boiled mash is still hot.
or making Sour mash
If you mom,
sister, girl friend or wife has ever made sour dough bread, she has
come pretty close to making a sour mash and is a stones’ throw from
hooch, if I am using that term correctly. But that is the difference
between us and them. They will walk up to the line and not cross it
(No offense, Miss Susan, I know you are reading this). We will,
because BOURBON, DAMMIT!!!
any process where micro-organisms are grown. In a sour mash
fermentation, Lactic Acid Bacteria and Yeasts grow up together for
their and our mutual benefit. The Lactic acid bacteria grow faster
than the yeast, and quickly produce lactic acid. They also use up the
oxygen. This is important, as yeast makes carbon dioxide and water if
it has oxygen. Nate is not pleased if good grain sugar for a bourbon
sour mash is being converted to CO2! Without oxygen, the
yeasts make ethanol, and Nate is happy! (Note to self: unhappy
Alphas are not much fun, and it is probably dangerous to laugh at
them) This cooperation between the two inhibits their competitors,
and allows the Lactic Acid Bacteria and yeast to dominate the
process, and keep the potential spoilage bacteria from growing. You
could perhaps explain this cooperation to the simple minded as
something like tag team professional wrestling, but on a very small
scale with a whole lot of tag teams.
The lactic acid
bacteria can and do make a number of other flavor compounds, in
addition to producing lactic acid. They actually produce two types of
lactic acid, the “d” (Latin abbreviation for right) and “l”
(Latin for left) forms. The lactic acid can and does react with the
ethanol, to produce esters. The “d” and “l” esters have
different aromas. You probably already know this, but Lactic acid
bacteria also ripen cheese and other fermented dairy products,
transforming relatively bland milk into pure Cheese awesomeness.
(Sorry my Southron friends, but no one makes a great Cheddar Cheese
like New England Yankees, and I say that as an Ohioan who believes
the South was right and who did 1 year hard time in Vermont workin’
at a cheese plant). The take home message is that the yeast and
Lactic acid bacteria can contribute a lot more to the Bourbon flavor
that acid and alcohol.
Lactic acid bacteria have a few things in common. For instance, they
have a peculiar habit of trying to kill each other off every so
often. Some species of Lactic acid bacteria make chemicals called
bacteriocins that can inhibit the growth of closely related Lactic
Acid Bacteria species. This would be like my Scotts-Irish cousins
many generations removed, developing a superweapon to completely
dominate my Irish Catholic cousins, many generations removed. The
lactic acid bacteria can also be attacked by viruses called
“bacteriophage.” Bacteriophage can wipe out a specific strain of
lactic acid bacteria that dominates fermentation, and allow another
strain to grow up and dominate. Some strains of lactic acid bacteria
actually have bacteriophage hidden in their DNA just waiting for the
right moment to pop out of hiding and take out a competing strain.
Yeasts also have
ways of competing with each other, although I am not familiar with
these mechanisms of competition. A dominant yeast strain can also be
killed off by a virus. The take home point in all this is that if you
have a favorite artisanal bourbon, and the flavor changes over time,
it could be due to a formerly dominant strain of Lactic Acid bacteria
or yeast being wiped out by a virus or other form of competition, and
replaced by a competitor.
normally save some of the previous batch of sour mash, and use it to
introduce yeast and lactic acid bacteria into a mash after it has
been boiled, and cooled. There are a number of simple techniques an
artisanal distiller can use to preserve their mash, such as using
good manufacturing practice borrowed from the dairy industry for
starter culture preservation, freezing and storing portions of the
mash, and having different mashes that they use on a rotating
distiller would have a number of practices in place to protect the
integrity of their sour mash. As an example, they may have what is
known as a mother culture. The mother culture is used to grow up a
“starter culture” in a small closed tank, from there it can be
pumped it into the mash fermentation vat. External sources of
contamination like airborne dust containing dehydrated wild yeast of
lactic acid bacteria, are controlled through careful plant design,
good manufacturing practices and air filtration.
A home brewer
could make their own sour mash from scratch, using a process similar
to making a sour dough starter culture.
We want the sour
mash fermentation to stop before the yeasts and LABs run out of
glucose. If they run out of glucose and the ethanol concentration is
not high enough to make them go dormant, the micro-organisms will
start breaking down amino acids or fibers from the grains for energy.
This is not good, and can lead to off-flavor formation (Think cowy,
cow barn, piggy, fecal, rotten egg, skunk, tomcat urine).
advantage to stopping the fermentation before the glucose is
exhausted it that free glucose will react with amino acids and other
substances produced by the fermentations when we start heating the
Bourbon beer for the distillation step. These reactions produce a
number of “sweet” (think of yourself at a county fair and walking
past the cotton candy stand) and “brown” (soy sauce-like) flavor
notes. A similar reaction is used industrially to make cocoa and a
multitude of manufactured flavors that go into processed foods.
We now have a
soup that is rich in flavor compounds, most likely smells similar to
beer, and has a lot of chemicals that can react with each other upon
distillation heating to create other flavors. The distillers
sometimes refer to it as the Bourbon beer. At this point, the
distiller uses a selective process called distillation, where the
bourbon beer is carefully heated to remove the ethanol. The
distillation process changes the flavor profile into something that
starts to resemble bourbon. (If at this point, for some unknown
reason, Nate told the distiller to make some Vodka-like distilled
spirits for his fellow Alpha buddy Vladimir Putin, the distiller
would install an series of activated filters in the still to remove
most of the flavor chemicals, we would indeed have a Vodka-like
A lot of things
happen during distillation: 1) we reduce the concentration of the
low boiling flavor compounds that are responsible for the “top
notes” of the beer flavor. The heat of distillation can also cause
some of these chemicals to form other, more complex aromas 2) We
concentrate the alcohol 3) We reduce the concentration of the high
boiling compounds from the Bourbon beer.
concentration of the high boiling and low boiling compounds in the
distilled ethanol depends on the design of the still. Generally, a
higher distillation column will be more selective than a shorter
column; it will more effectively separate the low boiling and high
boiling chemicals from the ethanol. The industrial distiller might
perform a “quick” distillation to strip of the alcohol, and then
do a second, slower distillation to remove more of the low boiling
and high boiling flavors. Obviously, by controlling the relative
amounts of the low boiling and high boiling flavor compounds in the
distilled ethanol, we control some of the flavor that is present in
the final product.
process does one more thing that never gets any press; it introduces
copper into the distilled ethanol and remaining flavors. Acids and
sulfur chemicals from the beer distillation will attack the copper in
the distillation column, and leach some copper into the distilled
ethanol. More on what this does in the next section.
Charring and Aging
Most of you
already know that bourbon is aged in charred oak barrels. Here is a
little more information on how this affects the flavor. There are
three natural polymers present in wood: cellulose, hemicellulose and
lignin. The barrel heating and charring affects each one differently,
in terms of the bourbon flavor.
Heating lignin releases the chemical vanillin (Think artificial
vanilla flavor, cake batter vanilla flavor, or Ben and Jerries’
chocolate chip cookie dough vanilla flavor) and smoky flavors. It
also produces most of the color. (Vanillin is a little different in
odor than the vanilla flavor extracted from fermented vanilla beans).
The reaction can also produce phenol, which sort of dulls the tongue,
and eugenol, a chemical in black pepper and other spices, and several
other potential flavor chemicals.
cellulose and hemicellulose causes the sugar molecules in them to
break down. This can form another class of compounds including and
related to the cotton candy flavor we talked about earlier. These
chemicals include sotolone and furaneol. These chemicals also occur
in aged cheeses with dry rinds, and give them a “sweet” flavor.
process also does something else that never gets any press, it
converts the inside of the oak barrel into a large catalytic surface.
The carbon surface inside the barrel, along with the copper from the
distillation column or still, most likely catalyze a number of
chemical reactions that inactivate sulfur compounds, and catalyze the
formation of some other flavor compounds. (As an example, methyl
glyoxal, and hydroxy acetone, two chemicals formed from cellulose and
hemicellulose heating, can react to form the furaneol cotton candy
flavor chemical) Some individuals claim that the aging process allows
a lot of the low boiling off flavors to evaporate slowly through the
wood. I think that much of the mellowing is due to the process I just
artisanal distiller may have a significant variation in charring for
the barrels used to age their bourbon, and this will affect the
flavor. The industrial distiller will probably use barrels for aging
that are made with relatively tight quality control practices,
leading to less flavor variability, and fewer surprises.
I would like for
Nate to write a section on Bourbon tasting. He is the expert on that.
I would, however, suggest that if you really want to train yourself
to pick out some of the complexities of Bourbon flavor, Google
“bourbon flavor wheel” or “whiskey flavor wheel”, and print
it out or save it to your phone of wheel. Look at the wheel when you
enjoy your next glass of bourbon, and see what you can pick out.
God Bless ya’