THE CHEMISTRY OF fermentation– part II

1. BREWING CHEMISTRY THE CHEMISTRY OF fermentation– part II

2. Fermentation Chemistry 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

3. Fermentation Chemistry 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)

4. Fermentation Chemistry When does Fermentation occur? After WORT COOLING Yeast is added to the cooled wort Where does Fermentation occur? In the FERMENTATION TANK

5. Fermentation Chemistry What is the chemical reaction process of alcohol fermentation? C6H12O6 C3H6O3 C2H4O3 + CO2C2H6O glucose pyruvate acetaldehyde ethanol

6. Fermentation Chemistry 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

7. Fermentation Chemistry 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

8. Fermentation Chemistry ESTERS:

9. Fermentation Chemistry ESTERS:

10. Fermentation Chemistry 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)

11. Fermentation Chemistry 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

12. Fermentation Chemistry 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

13. Fermentation Chemistry FUSEL (Higher) ALCOHOLS:

14. Fermentation Chemistry 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

15. Fermentation Chemistry PHENOLS: Smokiness Of Scotch Source in scotch whiskey: PEATED MALTS

16. Fermentation Chemistry PHENOLS: Phenols

17. Fermentation Chemistry 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

18. Fermentation Chemistry DIACETYL:

19. Fermentation Chemistry Why do we oxygenate our wort? Anaerobic Fermentation v. Aerobic Cellular Respiration Its all about ENERGY [No O2] [FERMENTATION] C6H12O6 C3H3O3 C2H4O3 + CO2C2H6O glucose pyruvate acetaldehyde ethanol [O2] What happens when you add O2? . . . CELLULAR RESPIRATION

20. Fermentation Chemistry