the science of brewing beer sarah oppelt current member of tolan lab, boston university former...
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![Page 1: The Science of Brewing Beer Sarah Oppelt Current member of Tolan Lab, Boston University Former Microbiologist & QC Manager, Brewery Ommegang](https://reader036.vdocument.in/reader036/viewer/2022062713/56649cdb5503460f949a5995/html5/thumbnails/1.jpg)
The Science of Brewing Beer
Sarah OppeltCurrent member of Tolan Lab, Boston University
Former Microbiologist & QC Manager, Brewery Ommegang
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The Science of Brewing Beer
Overview of Brewing Process & Ingredients
What contributes to the flavor of beers?
Fermentation
How Yeast is Really Controlling Everything
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Ingredients
Water
Malted Grains
Hops, or other additives
Yeast
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The Mineral Content of Water Will Have Subtle Effects on Flavor
Ca++ and Mg++ (hardness) will effect yeast metabolism and growth rate
HCO-3 (bicarbonate) will effect the pH of the fermentation
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Malted Grain Provides the Sugar for Fermentation
The more roasted a grain is, the more it contributes toasted and caramel flavors. However, darker roasted malts
provide less simple sugars.
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Hops Contribute Bitterness!
Hops are a surficant that also contribute to head formationbecause of their ability to stabilize bubbles
by increasing surface tension.Our ability to distinguish levels of bitterness is very imprecise.
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Yeast provides all of the flavor!
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3 Types of Yeast Used in BrewingAle yeasts are top-fermenting,
can ferment at higher temperatures, and tend to produce more esters.
Lager yeasts are bottom fermenting, ferment at lower temperatures,
and produce a more “crisp” taste.
Wild yeasts produce a lot of unusual compoundsand contribute to a “horse sweat” flavor
that is more acidic and an aquired taste.
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Fermentation in General
C6H12O6
glucose
C2H6O + CO2
ethanol carbondioxide
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Major Molecules that Contribute to Flavor & Mouth-feel
Length of carbon chain on alcohol
Amount of alcohol in the beer
Amount and type of esters produced
Residual sulfur compounds
Carbonation
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Metabolism Involved in Molecules that Contribute to FlavorGlucose
Pyruvate Ethanol
Acetyl-CoA
DHAP
G3P
+ Glyceraldehyde-3P
Esters
+ longer chain alcohols
Fatty Acids
Citric Acid Cycle
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Factors effecting Fermentation
Mineral Content of Water
Temperature of Fermentation
Pitch Rate of Yeast
Amount of Aeration
Length of Fermentation
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The faster a yeast grows and the longer the exponential growth phase is, the
more esters will be produced.
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The faster a yeast grows and the longer the exponential growth phase is, the
more esters will be produced.
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More Aeration Leads to Less Ester Production
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Common Esters & Their Flavors
Ethyl acetate is the most common ester, and smells like nail polish remover. However, sensory threshold
for this molecule is very high, so it isn’t usually noticed.
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Common Esters & Their Flavors
Isoamyl acetate has a very low threshold for detection. It has a “fake bananas” flavor and is found in
a lot of Belgian and wheat style beers.
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Common Esters & Their Flavors
Isoamyl acetate has a very low threshold for detection. It has a “fake bananas” flavor and is found in
a lot of Belgian and wheat style beers.
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Common Esters & Their Flavors
Ethyl butyrate has a low to medium threshold. It gives hints of passion fruit or pineapple.
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Common Esters & Their Flavors
Ethyl hexonoate has a low to medium threshold. It lends a red apple or anise like flavor.
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Budweiser
Grains & Hops: Pilsner malt, medium amount of hops
Yeast: S. ovarum, (formerly S. carlsberges)
Fermentation: 15°C for 2 wks, with longer lagering period. Wood chips are added to help yeast flocculate
Other: Filtered beer and force carbonated.
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Pabst Blue Ribbon
Grains & Hops: Pilsner malt, medium amount of hops, majority of sugar comes from corn
Yeast: S. ovarum, (formerly S. carlsberges)
Fermentation: 15°C for 2 -3 wks
Other: Filtered beer and force carbonated.
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Guinness
Grains & Hops: dark roasted malts give the color, light roasted malts provide sugar for fermentation
Yeast: S. cerevisea
Fermentation: 18°C for 2 -3 wks
Other: Filtered beer and force carbonated with nitrogen. The creaminess comes from the feeling of the smaller bubbles.
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HoegaardenGrains & Hops: lighter roasted malts and wheat, low
to medium hops
Yeast: S. cerevisea
Fermentation: 18°C for 2 -3 wks
Other: Beer is unfiltered and refermented in the bottle for natural carbonation
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Rodenbach
Grains & Hops: lighter roasted malts and wheat, low to medium hops
Yeast: “wild” fermentation, spontaneous mixed culture
Fermentation: 18°C for 2 -3 wks
Other: Beer is filtered and refermented in the bottle for natural carbonation
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Thanks for listening!
Questions?