Alcoholic Fermentation

Question 1

Aside from ethanol, CO₂, and heat, what other outputs do yeast produce during alcoholic fermentation?

Answer 1

• Methanol
• Fusel alcohols
• Esters
• Fatty acids
• Sulfur compounds

Question 2

At what temperature is yeast dormant?

Answer 2

10º C / 50º F

Question 3

At what temperature does yeast begin to die?

Answer 3

30º C / 86º F

Question 4

Describe parallel fermentation.

Answer 4

• 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

Question 5

Describe sequential fermentation.

Answer 5

All of the sugar that the yeast will ferment into alcohol is present at the start.

Question 6

How can a distiller avoid bacteria infecting their fermentation?

Answer 6

By avoiding delays between the creation of sugary liquid and fermentation.

Question 7

How can fermentation take place in solid-state fermentation?

Answer 7

• 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

Question 8

How could a distiller preserve alcoholic liquid in order to prevent spoilage?

Answer 8

By keeping it stored in a sealed, air-tight vessel.

Question 9

How does a distiller using cultivated yeast, know that they will be using the same yeast strain each time they carry out fermentation?

Answer 9

There is no limit to the number of times isolated cells can be used to grow new populations.

Question 10

How many yeast cells can there be in 1 mL of liquid during the most active phase of alcoholic fermentation?

Answer 10

100 million yeast cells.

Question 11

Like yeast, what are bacteria able to produce?

Answer 11

A large number of aromatic compounds.

Question 12

What is long fermentation?

Answer 12

Long fermentation is when some distillers allow bacteria to be active after yeast fermentation.

Question 13

Malic acid is a key nutrient for what?

Answer 13

Spoilage bacteria

This is why malolactic conversion is important for the stability of the wine.

Question 14

Name a type of product that benefits from long fermentation?

Answer 14

• 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.

Question 15

Nearly all spirits gain some or most of their aromatic characteristics from what?

Answer 15

Fermentation esters.

Question 16

True / False:

Nitrogen is always found in raw materials.

Answer 16

False

Distillers sometimes have to add nitrogen when it exists at low and no levels in the raw material. Example: sugar cane.

Question 17

True / False:

If the raw material contains sugar, the distiller has to use sequential fermentation.

Answer 17

True

Question 18

What advantages does yeast have when competing for sugars?

Answer 18

1. Yeast can tolerate acidic environments that other microorganisms can not.
2. When processing sugars, yeast produces ethanol as a by-product, creating an alcoholic environment that microorganisms cannot thrive in.

Question 19

What is cultured yeast?

Answer 19

A yeast that has been identified for its desirable properties and isolated and stored in secure specialist facilities.

Question 20

What is formed when yeast combines fatty acids with alcohols?

Answer 20

Esters

Question 21

What are fusel oils?

Answer 21

Fusel oils are usually a mixture that includes fusel alcohols, fatty acids, and esters.

Question 22

What are heavy or higher alcohols called?

Answer 22

Fusel alcohols

Some examples are propanol, butanol, and iso-amyl alcohol.

Question 23

What are some characteristics of esters?

Answer 23

Esters typically have fruity and floral aromas and play a big role in the aromatic make-up of a spirit.

Question 24

Why are the levels of methanol tightly regulated and managed during distillation and/or maturation?

Answer 24

Methanol can create unpleasant aromas and can potentially be harmful to humans.

Question 25

What are the **nutritional requirements** of yeast?

Answer 25

* **Fermentable sugars** * **Nitrogen**

Question 26

What are the products of **sugar metabolism** by yeast?

Answer 26

* **Ethanol** * **Carbon dioxide** * **Heat**

Question 27

What are the **two main reasons** a distiller would **not** use ambient yeast for fermentation?

Answer 27

1. There is no guarantee that the right microorganism will dominate the fermentation 2. These fermentations take longer to get going and other yeast or bacteria can become active and produce undesirable characteristics

Question 28

What are the **typical** sugars that yeast uses for energy?

Answer 28

* **Fructose** * **Sucrose** * **Or glucose**

Question 29

What are two **fatty acids** produced during fermentation?

Answer 29

**Acetic acid** and **butyric acid.**

Question 30

What are two spirits that are made using **ambient yeasts**?

Answer 30

**Mezcal** and **Baijiu**.

Question 31

What is **yeast**?

Answer 31

**Yeast** are single-celled microorganisms.

Question 32

What can happen with the sugary liquid when there is a **stuck** fermentation?

Answer 32

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.

Question 33

What can result from **high levels** of fusel alcohols?

Answer 33

High levels of fusel alcohols can give spirits **unpleasant** aromas and a **coarse** texture.

Question 34

What compounds have to be **removed** after fermentation because there is no way to stop a yeast cell from producing them?

Answer 34

**Sulfur compounds**

Question 35

What do some Asian spirits producers actively **encourage** in some of their products?

Answer 35

They actively encourage **bacterial growth** in order to create pungent aromas.

Question 36

What do the **concentrating effects** of distillation have on a fermented beverage with regards to aromatic compounds?

Answer 36

They increase the importance of the aromatic compounds on a spirits' style and quality.

Question 37

What does the term **stuck fermentation** refer to?

Answer 37

**Stuck fermentation** happens when the yeast has nutritional deficiencies and either stops fermenting or dies.

Question 38

What does yeast **produce** when **fed** in a sugary liquid?

Answer 38

**Ethanol**

Question 39

What gas is a **major** **output** of fermentation?

Answer 39

**Carbon Dioxide** ## Footnote *It is important for distilleries to be well ventilated so that CO₂ can be safely dispersed into the atmosphere.*

Question 40

What is **ambient yeast?**

Answer 40

**Ambient yeast** is the wild yeast that has naturally proliferated in the distillery environment. ## Footnote *If a sugary liquid is left exposed, the ambient yeast will start to grow in it and start alcoholic fermentation.*

Question 41

What is an essential **component** of proteins and DNA that is needed for yeast growth?

Answer 41

**Nitrogen**

Question 42

What is one of the **main acids** in wine?

Answer 42

**Malic acid**

Question 43

What is produced when yeast **metabolizes** sugar?

Answer 43

* **Ethanol** * **Carbon dioxide** * **Heat**

Question 44

What is the **advantage** of sequential fermentation?

Answer 44

It's easy to **predict** the level of alcohol at the end of fermentation.

Question 45

What is the best **defense** against bacterial contamination?

Answer 45

Allowing yeast to **rapidly dominate** the start of fermentation.

Question 46

What is the **ideal temperature** for alcoholic fermentation dependent on?

Answer 46

The ideal temperature **varies** between spirit categories and distiller practices.

Question 47

What is the most important **output** of alcoholic fermentation?

Answer 47

**Ethanol**

Question 48

What is the **range** for the amount of ethanol that can be **produced** during fermentation?

Answer 48

4% abv to 20% abv.

Question 49

What is typically used as the raw material in a **semi-solid fermentation**?

Answer 49

**Grains**

Question 50

What results in **higher levels of methanol** during fermentation?

Answer 50

Fruit juices that have higher levels of **pectin**. ## Footnote *European fruit spirits and Calvados are examples of this.*

Question 51

What things will a distiller do to provide **ideal conditions** for yeast to grow?

Answer 51

1. Provide nutrients 2. Manage temperatures 3. Lower levels of acidity in the sugary liquid

Question 52

What type of Asian spirit **relies** on pungent bacterial aromas?

Answer 52

**Baijiu**

Question 53

What yeast is **universally** favored by producers of alcoholic beverages?

Answer 53

***Saccharomyces cerevisiae*** ## Footnote *This yeast produces high levels of ethanol and has positive aromatic compounds.*

Question 54

When **fatty acids** combine with **alcohol**, it is called...

Answer 54

**Esterification**

Question 55

Where are esters **made**?

Answer 55

They are made in the **yeast cells**.

Question 56

Where can examples of **semi-solid fermentation** be found?

Answer 56

Producers of ***baijiu*** and ***shochu****.*

Question 57

Where do most fermentations take place?

Answer 57

Most fermentations take place in **liquid**.

Question 58

**Where** does solid-state fermentation take place?

Answer 58

Solid-state fermentation takes place in **sealed containers** or **pits** and can take several months to complete.

Question 59

Why can parallel fermentation be more **challenging** to manage than sequential fermentation?

Answer 59

There is a risk that the yeast will consume the sugar **faster** than it can be produced by the enzymes, resulting in stuck fermentation.

Question 60

Why do a vast majority of distillers use **cultured yeast**?

Answer 60

Many producers make high-volume brands where **consistency** is highly valued.

Question 61

Why do distillers try to ensure bacteria **do not** come into contact with their surgery liquid or their fermented alcohol liquid?

Answer 61

Because bacteria can create a significant number of **undesirable aromatic compounds**.

Question 62

Why does a distiller actively encourage **malolactic conversion**?

Answer 62

It makes the wine more **stable** and helps **preserve** the liquid that can't be distilled immediately.

Question 63

Why does yeast process or metabolize nutrients?

Answer 63

Yeast metabolize nutrients to create the energy they need to live and reproduce.

Question 64

Why is it important to manage the **temperature** during fermentation?

Answer 64

If conditions get too hot, the **yeast will die**.

Question 65

Why might a distiller start fermentation **before** enzymatic hydrolysis is not completely done?

Answer 65

The sugary liquid is **vulnerable** to spoilage from microorganisms while the enzymes are processing the starches.

Question 66

Why would a distiller choose to use a number of yeast strains **at the same time**?

Answer 66

A distiller may use a number of yeast strains at the same time to get the **benefits of each strain**.

Question 67

Why would a distiller leave the alcoholic liquid **in the tank** after fermentation has ended?

Answer 67

This allows further flavors to develop, normally as a result of **bacterial** activity.

Question 68

Without what would there be **no** alcoholic beverages?

Answer 68

**Yeast**

Question 69

What are **glucose** and **fructose**?

Answer 69

Sugars **made by plants** during **photosynthesis**.