What is Cold Fermentation?

Fermentation is essential to making the magic elixir known as beer. Lagers go through a unique cold fermentation process that many people don't know about. This process is critical to this style of beer and gives the beer its signature character. Whether you're just curious about the brewing process or interested in brewing your own at home, we'll help you better understand the science behind cold fermentation and brewing.

What is cold fermentation?

Generally speaking, storage yeast works best between 48 and 58 degrees Fahrenheit. The initial fermentation period for lager is usually about a week, depending on the specific gravity of the beer.

After the first fermentation stage is the cold fermentation stage, also known as storage or cold conditioning. This secondary fermentation stage can last two to three weeks at 32 degrees Fahrenheit. During this unique cold-aging process, yeast and other proteins are precipitated, resulting in the beer style's signature crisp, smooth lager.

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Learn about the process

As you probably already know, during fermentation, yeast consumes sugars that produce carbon dioxide and various aroma and flavor molecules. When fermented at room temperature, the yeast quickly consumes the sugar and depletes it quickly, preventing the production of additional gas and flavor compounds.

When fermented at low temperatures, yeast produces carbon dioxide and other molecules more slowly and steadily. This much slower process results in a more complex combination of flavor compounds. The heat speeds up the chemical reaction, the faster the sugar is converted to alcohol. This is also the reason why lagers have lower alcohol content than ale.

The benefits of cold fermentation

Since many of the flavors and characteristics of beer are developed during the fermentation process, brewers go to great lengths to ferment their beers. Cold fermentation is a process so cherished and valued by brewers because it is known to:

• more pronounced taste

• excellent foam

• more noble taste

• lower alcohol content

• Improve clarity

• fuller body

• More mellow taste

During lagering, beer undergoes the subtle but important flavor-altering biochemical processes that characterize the crisp and clean we associate with premium lagers. This cold fermentation process reduces any often negligible effects on beer flavor, such as acetic and lactic acids, which have a much higher taste threshold for humans. Instead, the extended fermentation period these lagers go through produces more desirable and impactful flavors.

Traditionally, when beer enters storage, it usually still contains a small fraction of the sugars that were originally present at the start of fermentation. About four-fifths of the residual sugar consists of easily fermentable maltose; the remainder is mainly maltotriose. During cold fermentation, the total residual sugar content of beer typically drops by as much as 50%. As the yeast processes the remaining fermentable sugars, the beer will slowly carbonate, and if any oxygen is introduced during transfer to the storage tank, the yeast has the potential to remove it, limiting potential damage to the beer flavor and appearance.

If handled properly, the resulting lager has only the desired flavor and character. These traits developed in the process are prized by brewers because they are not only the hallmark of craft beer, but greatly influence the taste of the beer.

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What Is Cold Crashing?

A result of cold fermentation is clearer beer due to the rapid chilling of the liquid, which allows the solid particulates to separate from the liquid. Cold crashing is a similar process, prior to packaging, the fermented beer is rapidly chilled. This allows the brewer to easily remove the liquid from any yeast particulates.

Rapidly decreasing the temperature of a colloidal solution encourages the coagulation of particulates such as proteins and yeast, and as these particulates coagulate, they become heavy enough to drop out of the solution. Then, the brewer can easily extract the liquid without the solids creating a foggy and hazy appearance to the beer. This is how lagers can appear so crystal clear.

While cold fermentation is a slower process than cold crashing, it still results in a crystal clear beer and a light mouthfeel. The prolonged lagering stage not only encompasses the benefits of cold crashing your beer but also helps develop the flavor and the distinct characteristics of a lager.

Why is cold fermentation required to make lager beer?

Warm fermentation is not possible as lagers are known for their light texture and very clear appearance. Warm fermentation will keep the yeast incredibly active and cause the yeast to quickly consume the residual sugar, preventing further development of flavors and aromas. It also leads to higher alcohol levels and an over-release of bitter proteins, making the beer less enjoyable.

The crisp, clean and light taste of beer can be directly attributed to this cold fermentation process. Additionally, warm fermentation reduces volatile acids and increases fixed acids, disrupting the delicate flavor balance of the beer. Since this beer is known for its subtle flavors, any disruption to the flavor balance can have a major impact on the resulting beer.