1. Simple sugars Ethanol + CO2
Fermentation Chemistry
Lecture One: Fermentation Basics
What is Fermentation?
Alcohol Fermentation is the chemical conversion of simple sugars (like glucose) to ethanol and carbon dioxide (CO2)
Yeast perform the fermentation chemical reactions
Fermentation pathway:
Anaerobic (oxygen is not needed)
The primary method yeast acquire energy for living
Simple sugars Ethanol + CO2

2. Fermentation Chemistry
Lecture One: Fermentation Basics
2 types of FERMENTATION:
1. Alcohol Fermentation: performed by yeast and bacteria
2. Lactic Acid Fermentation: performed by animals like us (not pertinent to brewing)

3. Fermentation Chemistry
Lecture One: Fermentation Basics
When does Fermentation occur?
After WORT COOLING
Yeast is added to the cooled wort
Where does Fermentation occur?
In the FERMENTATION TANK

4. Fermentation Chemistry Lecture One: Fermentation Basics
What is the chemical reaction process of alcohol fermentation?
C6H12O C3H3O C2H4O3 + CO C2H6O
glucose
pyruvate
acetaldehyde
ethanol

5. Fermentation Chemistry Lecture One: Fermentation Basics
Are there other chemicals or compounds that yeast produce during alcohol fermentation, other than ethanol and CO2?
YES. Up to over 600 others!!
Including:
Esters
Fusel (higher)alcohols
Phenols
Diacetyl
*some are good, some are not so good
CO2

6. Fermentation Chemistry
Lecture One: Fermentation Basics
ESTERS:
Esters are the most common/important flavor chemical that brewing yeast produce
Esters are typically fruity in flavor and produced more by Ale Yeasts
Sometimes we want them, other times not; depending on the beer style
We Want Esters:
Most Ales
Hefewiesen beers
Belgian ales
We Do Not Want Esters:
Lagers
Unwanted esters can arise from:
Contaminated beer from bacteria
Too high Fermentation T

7. Fermentation Chemistry
Lecture One: Fermentation Basics
ESTERS:

8. Fermentation Chemistry
Lecture One: Fermentation Basics
ESTERS:

9. Fermentation Chemistry
Lecture One: Fermentation Basics
ESTERS in DISTILLING FERMENTATION:
ethyl acetate – nail polish remover, model paint and glue
isoamyl acetate – pear, banana
all others are a potential (see Ester List)

10. Increasing ESTERS in your beer/spirits:
Fermentation Chemistry
Lecture One: Fermentation Basics
Increasing ESTERS in your beer/spirits:
1. Choose ester-producing ale yeast
2. Under pitch your yeast
3. Increase Fermentation T
4. Under oxygenate at pitching

11. Fermentation Chemistry
Lecture One: Fermentation Basics
FUSEL ALCOHOLS:
Definition: alcohol with 3+ carbons
Fusel alcohols are formed from pyruvate and too high fermentation T’s
Taste profile: “jet fuel”
Issue: a major cause of hangover headaches

12. Fermentation Chemistry
Lecture One: Fermentation Basics
FUSEL (Higher) ALCOHOLS:

13. Fermentation Chemistry
Lecture One: Fermentation Basics
PHENOLS:
Phenols are produced from pyruvate in the fermentation pathway
Flavor profile: clove, medicinal, “band-aide”, smokey
Phenols can be wanted or unwanted, depending on the beer style
Phenols and beer styles:
Belgian ales
German hefeweisens
Wheat beers
Rauchbier

14. Fermentation Chemistry
Lecture One: Fermentation Basics
PHENOLS: Smokiness Of Scotch
Source in scotch whiskey: PEATED MALTS

15. Fermentation Chemistry Lecture One: Fermentation Basics
PHENOLS:
Phenols

16. Fermentation Chemistry
Lecture One: Fermentation Basics
DIACETYL:
Diacetyl arise from pyruvate in the fermentation pathway
Typically, you NEVER want diacetyl
Flavor profile: buttery, butterscotch, buttered popcorn
Yeasts naturally produce diacetyl and will reabsorb it, given a little time:
the “diacetyl rest”
Too high Fermentation Temperature will also produce too much diacetyl

17. Fermentation Chemistry
Lecture One: Fermentation Basics
DIACETYL:

18. Its all about ENERGY Why do we oxygenate our wort? [No O2]
Fermentation Chemistry
Lecture One: Fermentation Basics
Why do we oxygenate our wort?
Anaerobic Fermentation v. Aerobic Cellular Respiration
Its all about ENERGY
[No O2]
C6H12O C3H3O C2H4O3 + CO C2H6O
glucose
pyruvate
acetaldehyde
ethanol

19. Fermentation Chemistry
Lecture One: Fermentation Basics