Understanding the beer fermentation process

Before you get started with the exciting experience of crafting your own brew, you wonder what the basics of the beer fermentation process are and perhaps you are curious to learn what happens during the different steps of the production. This post is meant to sum up the basic mechanics of the process, described as it may be conducted at home. Please contribute to this article by sharing your experiences, comments and/ or questions.

The beer fermentation process 101

beer fermentation 101 flow chart

What is beer?

In very simple terms, beer is an “alcoholic beverage made from malted grain, flavored with hops and brewed by slow fermentation”

It is produced from 3 basic, pure ingredients:

  • Malted cereal
  • Hops
  • Yeast

… and of, course water.

The beer fermentation process includes 4 basic operations:


An important note on SANITIZING: After the wort has been boiled, it is critical to make sure all the equipment and containers are properly sanitized all along the whole process to avoid contamination, which would impair the action of the yeast and/ or affect the finished beer with undesirable flavors and aromas.

Mashing – the preparation of the wort

Brewing Beer Process Mashing

To occur, a fermentation needs sugars, yeasts and air. In beer making, sugars (mainly Maltose, with some Glucose and other types of sugar) come from the MALT (germinated cereal that is dried or roasted to different degrees). The sweet fermentation ready liquid is called WORT. It is extracted by the MASHING process.

It is recommended to start your first couple of brewing attempts from ingredient kits. By providing you directly with malt extract – dry or liquid, you won’t have to go through all the steps of making WORT. When you are more experienced, you will hopefully want to create your own beer recipes, using the ingredients of your choice.

To make WORT from scratch – here are the steps you’ll have to follow:

First, your MALT has to be crushed through the process of MILLING – resulting in what we call GRIST.

Then comes the MASHING itself, which is done by mixing the GRIST with warm water, releasing the sugars from the MALT.

To complete the preparation of the WORT, LAUTERING is performed. This consists in separating the grain from the MASH using water, a process referred to as SPARGING – and filtering the liquid. In home brewing a bag made of cloth, similar to cheese cloth may be used when the GRIST is soaked or steeped in the warm water, in this case no filtration is required.

Boiling – adding hops

Initially, the brewer would boil his WORT in order to kill any undesirable bacteria.

BOILING will reduce the amount of liquid to the target volume to be fermented.

A controlled temperature is necessary for the whole duration of the BOIL to extract the qualities and characteristics of the hop. Adding hop is referred to as HOPPING. Hop may be added at an early stage of the BOIL, to give more bitterness, or toward during the BOIL to give more flavors, or toward the end to give more aromas. DRY HOPPING refers to adding hop to the cooled WORT. Other flavorings such as spices, or sugar may be added too during the BOIL.

This step is particularly crucial during the beer making and requires special attention, as the temperature is key – a regular rolling boil is what you want, as you add ingredients to the WORT in home brewing, this is when you run the risk to boil over. To prevent this from happening, stirring the kettle as you start will help reduce the foaming. It will also prevent the MALT extract to caramelize at the bottom of the kettle.

The boil usually lasts for 60 minutes.

Fermenting – wort turning into beer, the yeasts doing the work

Beer Fermentation Process Krausen

Generally speaking – not only about beer – there are two different types of fermentation. The PRIMARY FERMENTATION (or ALCOHOLIC FERMENTATION) occurring by the action of the yeast cells, and the lactic acid fermentation occurring by the action of bacteria. Scientists a century ago discovered that enzymes (proteins promoting chemical reactions in cells) were actually responsible for fermentation, a transformation happening inside the yeast cells.

The PRIMARY FERMENTATION is the process that really transforms your WORT into BEER, now containing alcohol. This fermentation takes place in two different stages. In the first stage the glucose will be converted through glycolysis into pyruvic acid – an intermediate compound in the metabolism of carbohydrates and proteins. In the second stage, in an environment with no oxygen, the pyruvic acid will be converted into ETHANOL (alcohol) and CO2.

To start its ALCOHOLIC FERMENTATION, the WORT needs to be chilled down to around 70 degrees Fahrenheit. The yeast is then PITCHED (or added). The type of yeast will determine at what temperature the FERMENTATION should occur. Typically an Ale is fermented between 60 and 68 degrees Fahrenheit, and a Lager around 50 degrees.

The Alcoholic Fermentation may take between 4 days to sometimes up to 2 weeks, depending on the beer. A visual indicator of what stage of the fermentation you are at is the foamy, coarse head forming and bubbling on top of the beer, called KRAUSEN. It is caused by the growth of the yeast cells. At the end of fermentation the KRAUSEN falls.

A SECOND FERMENTATION is sometimes recommended to produce a clear beer, free of sediment, making a better beer, refining and polishing the taste.

The SECOND FERMENTATION is started when the PRIMARY is almost finished. It is important to make sure most of the yeast have been consumed but CO2 is still being, normally more slowly generated. Normally this is the case around day 4 or 5 of the beer alcoholic fermentation process. CO2 will protect your beer from oxidation and from obtaining off-flavors. At this point, the beer should be RACKED (transferred) into a container with smaller head space and stay there another week or two, before bottling. Lagers need more time to finish their fermentation, because it is performed at colder temperatures. Also beers with more sugar will take longer to ferment completely, because the remaining yeasts will struggle to eat all the sugar, being less active at a higher level of alcohol. The second fermentation may take 2 weeks or more. A Lager will need 6 to 8 weeks.

Conditioning – bottling or kegging

Beer Fermentation Process Bottling

This is the last step in beer making.

In home brewing, the most simple method is to BOTTLE your beer. At this point you have hopefully a clear, delicious beer. However, since most of the CO2 has escaped during the fermentation, it is quite flat. This is the reason why it should be CONDITIONED.

Right before BOTTLING, your beer will be primed with a mixture of sugar and water that will naturally re-ferment in the bottle. The CO2 produced will carbonate the beer and remain in the tightly capped bottle. It will take another 2 weeks at 70 to 75 degrees F. After that, the bottle can be chilled at 60 degrees F. or under to stabilize the beer.

A quicker alternative is to KEG your beer, a method in which you force the desired amount of CO2 into the keg filled with beer. For this you will need tap lines, a regulator (to control the carbonation), a CO2 cylinder, and a keg. Carbonation will typically take 2 to 3 days.

Both a craft and a natural process – go further with your understanding of fermentation

It’s easy to understand why brewing and fermenting is so exciting. The process combines the intervention of human work, tastes and skills – basically an art – with the work of natural elements interacting in a specific environment.

If you serious about drinking fresh, pure, healthy, and haven’t tried to brew your own yet, I strongly encourage you to start the journey.  This is so much FUN and SATISFYING.

A absolute must reading for beginners and more advanced brewers is the book by Charlie Papazian, Joy of Home Brewing. Go to my personal review of this “home brewer’s bible” for more information.

Cheers, and to our health!