The Science of Alcohol Fermentation: Understanding Single and Double Processes

The process of Making Alcohol

To explain the process of making alcohol very simply, we can say that sugar is transformed into alcohol. As I've already mentioned in another article, "Korean Home Brewing : Colonial Impact on Traditional Brewing Culture" when alcohol was first created, it happened unintentionally - something was accidentally left out and naturally underwent alcoholic fermentation.

Fruits like grapes and apples, or sugar cane and molasses, already contain sugar, so they can become alcohol without any special saccharification process. However, when the main ingredients are glutinous rice, regular rice, wheat, or other grains, their main component is starch, which requires a saccharification process to break down the starch into glucose and maltose.

This breakdown is aided by nuruk (a Korean fermentation starter) or malt. The saccharifying enzymes contained in nuruk or malt break down the starch into sugar. Yeast then consumes these sugars and produces alcohol and carbon dioxide, along with organic acids, esters, and aldehydes that enhance the taste and aroma of the alcohol. This chemical process of making alcohol is called "alcoholic fermentation."

Alcoholic Fermentation : Single and Double Fermentation

Alcoholic fermentation can be divided into "single fermentation" and double fermentation." When alcoholic fermentation occurs directly without a saccharification process, it's called "single fermentation," with wine being a classic example.

We already know the process where crushed grapes stored in a container naturally develop alcohol and become wine. To explain in more detail, the sugar (glucose) contained in fruits like grapes ferments over time due to certain microorganisms, naturally creating alcohol and becoming an alcoholic beverage.

This process, where wild yeast from the air converts the sugar in fruit into alcohol, is called 'single fermentation' because it's made through just one fermentation step.

Making Alcohol from Grains : Double Fermentation

While it would be ideal to make alcohol just from fruits, countries where fruits were difficult to obtain made alcohol from grains instead. People brewed alcohol using numerous grains like rice, barley, wheat, potatoes, sweet potatoes, and corn. Since these grains don't contain glucose that can directly undergo alcoholic fermentation, they require a process to convert the starch in the grain into glucose. This fermentation process is called "double fermentation," which is further divided into two types.

Double fermentation consists of "separate double fermentation" and "parallel complex fermentation." Seperate double fermentation refers to a process where saccharification and alcoholic fermentation occur in different stages. In other words, fermentation takes place only after saccharification is complete, so the saccharification and fermentation processes are distinct. Beer is a classic example of this separate double fermentation.

On the other hand, parallel complex fermentation occurs when saccharification and alcoholic fermentation take place in the same process - that is, they happen simultaneously in the same fermentation vessel. Korean rice wine (makgeolli), cheongju, yakju and Japanese sake all belong to this category of parallel complex fermentation.

Converting Starch to Glucose

To convert starch into glucose, we need to break down the bonds between sugars. This is why grains are ground into powder or heated - make it easier to convert starch into glucose. You might have experienced how rice gradually taste sweeter the longer you chew them in your mouth. This happens because the starch is broken down by enzymes in your saliva, creating a sweet taste. This should help you understand what it means when we talk about breaking sugar bonds.

Looking at it from the opposite perspective, we could say that starch is formed when glucose molecules bond together. To break down starch into glucose, we need enzymes that can effectively decompose starch. It's important to note that enzymes are not the same as microorganisms themselves. Enzymes can be described as catalysts made of proteins that rapidly accelerate certain reactions.

I'll explain more about enzymes and yeast in detail another time. For now, I've summarised alcoholic fermentation in this article. Although this might seem a bit complex, I hope this information proves helpful to anyone researching alcoholic fermentation.