A Short Guide to Fermentation of Beer

While ales generally take two-five days for fermenting, I wait for two weeks at least for enhanced taste. Fermenting lagers, however, take two to three weeks, and the conditioning lasts for weeks or months at the end. Keep reading if you want to know about the beer fermentation process to brew some of your own at home.

Fermentation of Beer- The Process Explained

Fermentation can be described as the process in which the yeast converts the �sugars’ into heat, alcohol, and carbon dioxide. The traditional beer brewing process involves �sugars’ that are obtained through malted barley. 

Sometimes other sources like plant sugars and cereals are also used for brewing beer. These components add protein-containing substances to the beverage. The proteinaceous substances along with flavoring agents (added) and the sugars, generate aromas, alcohol, and flavors typically found in beer. 

Fermentation of beer is as age-old process, with every civilization featuring alcohol consumption all through history. During the ancient times, beer consumption came with psychological and physiological advantages (limited drinking). It was also a safe drink compared to other water sources. And the fermentation process was highly significant in many cultures and religious practices. 

Today, we have a better understanding of the beer fermenting process, making it easier to prepare this beverage at home. Here are the most common fermentation processes explained for you.

What is Top Fermentation of Beer?

The top fermentation generally produces the famous drink- ale. In this fermenting process the yeast continues to function properly at �room temperature’. It starts denaturing once the ethanol concentration gets to 12 percent. After the activity comes to a stop, you can see the yeast collected at the fermenter’s top part. This collected yeast has a �dense foam’ consistency. 

Usually, the �infusion method’ is used for brewing top-fermented beers like ale. The temperature for fermenting is warm, and maintains at 15- 25 degree Celsius for 3-5 days. The fermentation process uses the Saccharomyces cerevisiae yeast, which is removed after it has foamed up on the surface. 

This fermentation process produces beers that have �high alcohol content’, dark color, low carbon dioxide content, and complex aromas. The drinking temperature for these beers are 6-12 degree Celsius. Some top-fermented beers include ales, wheat beer, Trappist, bitter, and stout among others. 

What is Bottom Fermented Beer?

As the name suggests, the fermentation process for these beers involve the yeast settling at the vat’s base. This fermentation process grew popular after famous drink, Pilsner from Pilzen town in Czech, became famous in the 19th Century’s middle part. The Saccharomyces pastorianus yeast is generally mixed with the malt used for preparing bottom fermented beer. 

The process continues for 7-10 days at a cold temperature of 4-12 degree Celsius. It is during the fermenting process that the yeast settles down at the vat’s bottom part. This fermentation method produces less fruity beers with high carbon dioxide content. 

The drinking temperature for these beers are 4-7 degree Celsius, meaning these beers are served chilled. Some popular bottom fermented beers include lager, Vienna, and Bockbier.

What is the Difference between Top and Bottom Fermented Beer?

To compare the two fermentation methods, here are some vital differences:

  • Method- The top fermentation process makes yeast settle at top, and the bottom fermentation results in yeast settling at the bottom. 
  • Yeast Variety- The top fermentation uses the Saccharomyces cerevisiae, and is the older of the two fermentation methods. The bottom fermented beer is made using the Saccharomyces pastorianus yeast. 
  • Fermentation Time- Top fermenting takes place over 3-5 days for fermenting, while the bottom fermented beer is fermented over 7-10 days. 
  • Temperature- Top fermenting requires a warm 15-25 degree Celsius, and the bottom fermented beer requires 4-12 degree Celsius for fermenting. Drinking temperature for the former is 6-12 degree Celsius, and the latter is 4-7 degree Celsius.
  • Color- Top fermented beers are generally dark brown or reddish brown, while the bottom fermented beers are lighter in color.

What is Spontaneously Fermented Beer?

This beer type generally applies to specific Belgian beers such as Lambic, Gueuze, and Kriek. Unlike bottom or top fermentation processes, no yeast is mixed with the malt (or wort). The �wild yeast’ used for the fermentation process is available in the air. The wort is allowed to cool in the air, and this exposure leads to inoculation with bacteria and wild yeast. 

Later on, the brew is shifted to oak barrels (large ones). The fermentation process can last between 1 and 3 years. Organisms like Brettanomyces bruxellensis, present in the air trigger the fermentation process, leading to inoculation and the wort’s yeasting process.

It takes much more time than the bottom or top fermentation of beer, and is exclusive to certain beer varieties. 

What is Bottle Fermentation?

Bottle fermentation is also called �bottle conditioning’, and involves creating carbonation in a traditional way. In this fermentation process, sugar is added in small amounts to the brew. The carbon dioxide produced naturally, combines with the sugar to make the beer carbonated. 

The process begins with a beer batch that has completed its primary fermentation process, and is ready for bottling. To know this, you will have to take gravity readings over a few days, followed by charting your results. 

Then the secondary fermentation process begins when yeast and sugar are added to the beer. You can use any sugar variety including �dry malt extract’, dextrose, honey, table sugar, fruit juice, molasses, and brown sugar. This will complement the existing beer flavor profile. 

To calculate the sugar dosing, take these factors into account:

  • Final carbonation level
  • The carbon dioxide level already present in the beer
  • Fermentable sugar, if any, added during primary fermentation

Once you have added the exact yeast and sugar amounts, you have to seal the bottle. This will allow the yeast to work on the sugar. The secondary fermentation process starts once you place the bottles either at room temperature or a little above it. This will lead to the yeast functioning to produce alcohol (small amount) and carbon dioxide. 

The yeast will take in all the oxygen contained within the bottle, thereby eliminating any chance of beer degradation. The absence of oxygen leads to the beer aging effectively. Bottle fermentation takes place over several weeks. Yeast will, over time, die and collect as sediment in the bottle’s bottom part. 


Now that you know the fermentation of beer clearly, brew your own beer at home will become easier. You will require a few cost-effective equipment, specific ingredients, and the fermentation process to follow. Add this skill to your list, and enjoy a palate-enhancing beer along with your friends.