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
What are the typical sugars that yeast uses for energy?
- Fructose
- Sucrose
- Or glucose
What are two fatty acids produced during fermentation?
Acetic acid and butyric acid.
What are two spirits that are made using ambient yeasts?
Mezcal and Baijiu.
What is yeast?
Yeast are single-celled microorganisms.
What can happen with the sugary liquid when there is a stuck fermentation?
Other microorganisms can grow and create unpleasant aromas. It can also be a costly problem in terms of lost material and time for the distiller.
What can result from high levels of fusel alcohols?
High levels of fusel alcohols can give spirits unpleasant aromas and a coarse texture.
What compounds have to be removed after fermentation because there is no way to stop a yeast cell from producing them?
Sulfur compounds
What do some Asian spirits producers actively encourage in some of their products?
They actively encourage bacterial growth in order to create pungent aromas.
What do the concentrating effects of distillation have on a fermented beverage with regards to aromatic compounds?
They increase the importance of the aromatic compounds on a spirits’ style and quality.
What does the term stuck fermentation refer to?
Stuck fermentation happens when the yeast has nutritional deficiencies and either stops fermenting or dies.
What does yeast produce when fed in a sugary liquid?
Ethanol
What gas is a major output of fermentation?
Carbon Dioxide
It is important for distilleries to be well ventilated so that CO2 can be safely dispersed into the atmosphere.
What is ambient yeast?
Ambient yeast is the wild yeast that has naturally proliferated in the distillery environment.
If a sugary liquid is left exposed, the ambient yeast will start to grow in it and start alcoholic fermentation.
What is an essential component of proteins and DNA that is needed for yeast growth?
Nitrogen
What is one of the main acids in wine?
Malic acid
What is produced when yeast metabolizes sugar?
- Ethanol
- Carbon dioxide
- Heat
What is the advantage of sequential fermentation?
It’s easy to predict the level of alcohol at the end of fermentation.
What is the best defense against bacterial contamination?
Allowing yeast to rapidly dominate the start of fermentation.
What is the ideal temperature for alcoholic fermentation dependent on?
The ideal temperature varies between spirit categories and distiller practices.
What is the most important output of alcoholic fermentation?
Ethanol
What is the range for the amount of ethanol that can be produced during fermentation?
4% abv to 20% abv.
What is typically used as the raw material in a semi-solid fermentation?
Grains
What results in higher levels of methanol during fermentation?
Fruit juices that have higher levels of pectin.
European fruit spirits and Calvados are examples of this.
What things will a distiller do to provide ideal conditions for yeast to grow?
- Provide nutrients
- Manage temperatures
- Lower levels of acidity in the sugary liquid
What type of Asian spirit relies on pungent bacterial aromas?
Baijiu
What yeast is universally favored by producers of alcoholic beverages?
Saccharomyces cerevisiae
This yeast produces high levels of ethanol and has positive aromatic compounds.
When fatty acids combine with alcohol, it is called…
Esterification
Where are esters made?
They are made in the yeast cells.
Where can examples of semi-solid fermentation be found?
Producers of baijiu and shochu.
Where do most fermentations take place?
Most fermentations take place in liquid.
Where does solid-state fermentation take place?
Solid-state fermentation takes place in sealed containers or pits and can take several months to complete.
Why can parallel fermentation be more challenging to manage than sequential fermentation?
There is a risk that the yeast will consume the sugar faster than it can be produced by the enzymes, resulting in stuck fermentation.
Why do a vast majority of distillers use cultured yeast?
Many producers make high-volume brands where consistency is highly valued.
Why do distillers try to ensure bacteria do not come into contact with their surgery liquid or their fermented alcohol liquid?
Because bacteria can create a significant number of undesirable aromatic compounds.
Why does a distiller actively encourage malolactic conversion?
It makes the wine more stable and helps preserve the liquid that can’t be distilled immediately.
Why does yeast process or metabolize nutrients?
Yeast metabolize nutrients to create the energy they need to live and reproduce.
Why is it important to manage the temperature during fermentation?
If conditions get too hot, the yeast will die.
Why might a distiller start fermentation before enzymatic hydrolysis is not completely done?
The sugary liquid is vulnerable to spoilage from microorganisms while the enzymes are processing the starches.
Why would a distiller choose to use a number of yeast strains at the same time?
A distiller may use a number of yeast strains at the same time to get the benefits of each strain.
Why would a distiller leave the alcoholic liquid in the tank after fermentation has ended?
This allows further flavors to develop, normally as a result of bacterial activity.
Without what would there be no alcoholic beverages?
Yeast
What are glucose and fructose?
Sugars made by plants during photosynthesis.
