Precision Flavor Through Fermentation Control

As a young brewer, I was surprised to see how freely other brewers would share their recipes.
Why would you give away your secrets? The truth is that a great beer is so much more than a list of ingredients. While quality ingredients are important, so much of the flavor expression in a beer comes from the brewing process itself.

Brewing flavor: It’s all about process

Nowhere is this more apparent than the fermentation process. Yeast is the only living part of the brewing process (aside from the brewer, who is just there to hold the mash fork). Different yeast strains express different genes that determine the level of attenuation and production of flavor compounds such as esters, fusel alcohols, aldehydes, phenolics, and off-flavors such as diacetyl and hydrogen sulfide (H₂S).

Biological systems are sensitive to their environment, and changes to the fermentation conditions will affect flavor expression from the yeast. Controlling the fermentation environment will help you to achieve the flavor profile you are aiming for.

Tips for fermentation and sensory control

Temperature – Higher temperatures tend to promote yeast growth, leading to higher levels of fusel alcohols and esters. Lower temperatures result in less diacetyl production and lower levels of acetaldehyde (H₂S, SO₂).

Pitching Rate – Lower pitching rates lead to more fruity ester perception. Higher pitch rates will decrease fusel production by reducing overall yeast growth, but solvent-like aromas may increase due to higher ethyl acetate levels.

Pressure – Fermentation under pressure can decrease fusels and esters but may increase diacetyl levels.

Wort Composition – Nutrient levels in the wort will affect flavor development. Higher zinc levels will promote full attenuation and decrease acetaldehyde but may increase fusels and esters. High free amino nitrogen (FAN) levels may increase acetaldehyde and diacetyl production. Some off-flavors are related to nutrient deficiencies, such as diacetyl (lack of valine) or H₂S (lack of sulfur amino acids or some vitamins). Current research suggests that low FAN levels may promote thiol expression by some yeast strains by removing nitrogen repression of the IRC7 (beta lyase) gene.

Contact Time – Patience is your friend. Off-flavors such as acetaldehyde, diacetyl and H₂S are a byproduct of a normal, healthy fermentation. They are usually reabsorbed at the end of fermentation if given the chance, so give the yeast sufficient contact time with the beer and avoid premature transfer.

The wheat beer example: Balancing banana and cloves

Let’s say you want to make a great wheat beer that strikes a balance between banana and clove characters. The most important factor is the yeast strain selection. Choose LalBrew Munich Classic™ or LalBrew Abbaye™ for higher isoamyl acetate (banana), or LalBrew Wit™ for a subtle banana character. Both isoamyl acetate and 4-vinyl guaiacol (4-VG, clove) levels are associated with lower pitch rates and higher fermentation temperatures. To boost esters, include isoamyl acetate, a lower pitching rate is more effective than higher temperatures. So, if you want to boost banana character without raising the clove flavor too much, use a lower pitch rate and ferment at cooler temperatures.

These general flavor control principles are a good starting point, but there are also exceptions to every rule. With so many variables, there will always be some optimization required to dial in your flavor profile. With a global support network of brewing experience, the Lallemand Brewing technical team is always available to provide personalized support to help you to get the flavor you want from your fermentation.

To learn more about flavor control, take our dedicated 10 minutes eLearning module.