Fermentation is the heart of the brewing process. Throughout fermentation, wort produced from raw materials is converted to beer by yeast. Fermentation is usually separated into three stages: primary, secondary, and conditioning (or lagering). Fermentation is as soon as yeast produce all of the alcohol and aroma and also flavor compounds discovered in beer. Manipulation the temperature, oxygen levels, and also pitch rate as well as yeast strain selection will all dramatically impact the manufacturing of aroma and flavor compounds developed during fermentation.

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Primary Fermentation

The major stage the fermentation begins when the yeast is introduced into cooled, aerated wort. The yeast easily utilize the easily accessible oxygen to create sterols, a crucial compound for culture expansion. When the oxygen is gone, the yeast switch to the anaerobic phase where the bulk of wort sugars are decreased to ethanol and also CO₂. Yeast expansion occurs during primary fermentation. The extent and also rate of yeast expansion is directly related to the manufacturing of aroma and flavor compounds.

Primary Fermentation Summary: 

Depletion of liquified oxygen Acidification/reduction in pH Yeast development or culture expansion Ethanol and CO₂ production Production of odor compounds such together esters, diacetyl, sulfur comprise compounds, etc. Consumption of many wort sugars 

The temperature the the main fermentation must be regulated follow to the preferred flavor and also aroma profile. The following is a guideline:

Primary Fermentation Temperatures: 

Ales: 62-75 °F (17-24 °C) Lagers: 46-58 °F (8-14 °C) *Note: Lager fermentations have the right to be began warmer (~60 °F/15.5 °C) until indicators of fermentation (gravity drop, CO₂ production, head formation) room evident. Cool to wanted fermentation temperature once indicators of fermentation space observed. Wheat and Belgian styles: 62-85 °F (17-29 °C) 

Secondary Fermentation

The an additional stage the fermentation describes the stage of fermentation after ~ the bulk of the wort sugars have actually been consumed and also there is a sharp decrease in the price of fermentation. Throughout this period, many of the final sugars room depleted and some second metabolites space converted by the yeast. Yeast flocculation and also settling begins to occur because of the increase in alcohol content and the depletion of sugar and nutrients. Diacetyl reduction takes ar during secondary fermentation and also during the diacetyl rest that some brewers incorporate into the an additional stage the fermentation.

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Secondary Fermentation Summary: 

Decreased rate of ethanol and also CO₂ production Diacetyl Conversion Reduction of part flavor compound by yeast line or CO₂ scrubbing Terminal gravity is reached Yeast flocculation and also settling begins 

Secondary Fermentation Temperatures:

Ales: very same as primary fermentation (higher temperature will increase diacetyl palliation rates) Lagers: 40-60 °F (4-15 °C). Some brewers permit the beer to increase in temperature to rate the diacetyl reduction. This raised temperature is usually only sustained for 24 come 48 hours. Wheat and Belgian Beers: same as main fermentation (higher temperature will boost diacetyl reduction rates). 


The conditioning phase takes place when the terminal gravity has actually been reached and the tank is cooled come refrigeration temperature (31-38 °F, 0-3 °C). During this time the yeast proceeds to flocculate and also settle. The yeast additionally conditions the beer by reducing miscellaneous undesirable flavor compounds. Ales carry out not benefit from lengthy conditioning times like lagers do. The preferable flavors in ales will decrease v age and therefore the is recommended that conditioning it is in as quick as possible before packaging. Exposure come oxygen in ~ this stage is extremely detrimental come beer quality.

Conditioning Summary: 

Most that the yeast is removed from beer Formation and precipitation that haze developing proteins Reduction and also mellowing of harsh flavors Reduction of sulfur compounds, diacetyl, and also acetaldehyde Flavor stabilization