Alcoholic Fermentation Flashcards
This deck covers the fundamentals of fermentation and how yeast and bacteria are used to produce alcohol as well as certain flavors or other characteristics of certain spirits around the world.
Aside from ethanol, CO2, and heat, what other outputs do yeast produce during alcoholic fermentation?
- Methanol
- Fusel alcohols
- Esters
- Fatty acids
- Sulfur compounds
At what temperature is yeast dormant?
10º C / 50º F
At what temperature does yeast begin to die?
30º C / 86º F
Describe parallel fermentation.
- Developed in Asia to produce baijiu, soju, and shochu
- Distillers use filamentous fungi to create amylase enzymes
- The approach is only used with raw materials that contain starch
- The starch is converted to sugar at the same time as the sugar being fermented alcohol
Describe sequential fermentation.
All of the sugar that the yeast will ferment into alcohol is present at the start.
How can a distiller avoid bacteria infecting their fermentation?
By avoiding delays between the creation of sugary liquid and fermentation.
How can fermentation take place in solid-state fermentation?
- The fermenting material is made up of individual bits with gaps between them and the material is moist
- Yeast relies on cell division to move through the grains
How could a distiller preserve alcoholic liquid in order to prevent spoilage?
By keeping it stored in a sealed, air-tight vessel.
How does a distiller using cultivated yeast, know that they will be using the same yeast strain each time they carry out fermentation?
There is no limit to the number of times isolated cells can be used to grow new populations.
How many yeast cells can there be in 1 mL of liquid during the most active phase of alcoholic fermentation?
100 million yeast cells.
Like yeast, what are bacteria able to produce?
A large number of aromatic compounds.
What is long fermentation?
Long fermentation is when some distillers allow bacteria to be active after yeast fermentation.
Malic acid is a key nutrient for what?
Spoilage bacteria
This is why malolactic conversion is important for the stability of the wine.
Name a type of product that benefits from long fermentation?
- Some Scotch Whisky benefit from long fermentation because it adds complexity to the final spirit.
- Some rum producers also do this in order to produce pungent aromas.
Nearly all spirits gain some or most of their aromatic characteristics from what?
Fermentation esters.
True / False:
Nitrogen is always found in raw materials.
False
Distillers sometimes have to add nitrogen when it exists at low and no levels in the raw material. Example: sugar cane.
True / False:
If the raw material contains sugar, the distiller has to use sequential fermentation.
True
What advantages does yeast have when competing for sugars?
- Yeast can tolerate acidic environments that other microorganisms can not.
- When processing sugars, yeast produces ethanol as a by-product, creating an alcoholic environment that microorganisms cannot thrive in.
What is cultured yeast?
A yeast that has been identified for its desirable properties and isolated and stored in secure specialist facilities.
What is formed when yeast combines fatty acids with alcohols?
Esters
What are fusel oils?
Fusel oils are usually a mixture that includes fusel alcohols, fatty acids, and esters.
What are heavy or higher alcohols called?
Fusel alcohols
Some examples are propanol, butanol, and iso-amyl alcohol.
What are some characteristics of esters?
Esters typically have fruity and floral aromas and play a big role in the aromatic make-up of a spirit.
Why are the levels of methanol tightly regulated and managed during distillation and/or maturation?
Methanol can create unpleasant aromas and can potentially be harmful to humans.
What are the nutritional requirements of yeast?
- Fermentable sugars
- Nitrogen
What are the products of sugar metabolism by yeast?
- Ethanol
- Carbon dioxide
- Heat
What are the two main reasons a distiller would not use ambient yeast for fermentation?
- There is no guarantee that the right microorganism will dominate the fermentation
- These fermentations take longer to get going and other yeast or bacteria can become active and produce undesirable characteristics