Strategies for Sulfur Reduction in Lager

Sulfur compounds are part of normal yeast metabolism and cannot be avoided. At low levels, compounds such as hydrogen sulfide (H₂S) can be part of the standard flavor profile of a beer adding complexity to the flavor profile. At a threshold level, H₂S is considered part of the fresh and crisp flavor profile of many traditional lagers. At high enough concentrations, H₂S gives a strong aroma of rotten eggs. H₂S levels can be kept low by ensuring a healthy fermentation with adequate nutrient levels. There are also ways to remove H₂S from a finished beer if the fermentation does not go as planned.

Keep H₂S Low With Nutrients

It is best to prevent H₂S from forming in the first place, rather than having to remove it later! H₂S is formed when the yeast produces the sulfur-containing amino acids cysteine and methionine. If these amino acids are already present in the wort, the yeast doesn’t activate these pathways and less H₂S will be produced. Higher H₂S levels are also linked to deficiency of specific vitamins, such as thiamine (B1) and pantothenic acid (B5).

To keep H₂S levels low, use a nutrient that contains amino acids and vitamins. These may be present in yeast extracts and autolysates or may be supplemented. Some nutrients that contain high levels of diammonium phosphate (DAP) may provide enough FAN, but not significant amounts of amino acids or vitamins. Yeastlife Extra™ provides a good balance of FAN, amino acids, and vitamins. Plus, Yeastlife O™ provides these elements from a 100% yeast-derived source.

Sulfur-Negative Yeast

Since H₂S is produced by yeast metabolism, it is normal that different strains produce different levels of H₂S. Strains with low nutrient requirements will tend to produce less sulfur since they will be less affected by low levels of amino acids. There are also some yeast strains that are genetically H₂S negative. LalBrew NovaLager™ is a great example – this hybrid yeast (non-GMO) was selected to produce clean, H₂S-free lagers since it lacks specific genes in the metabolic pathways for sulfur amino acids.

H₂S Removal

What do you do if, despite your best efforts, you end up with H₂S in the finished beer? Fortunately, yeast will tend to reabsorb H₂S at the end of fermentation. If given enough time in contact with the beer, H₂S levels will be reduced – but this may take time and results will depend on yeast health, flocculation, and the amount of H₂S in the beer. CO₂ can be passed through the beer to remove H₂S, but this also removes positive aromas such as esters and terpenes and may reduce foam potential.

Adding copper is an efficient way to remove H₂S by precipitating it as copper sulfide (CuS). This could be as simple as passing the beer through a copper pipe, but more complex copper electrolysis systems exist. Adding copper salts directly to the beer is not ideal as higher copper levels can promote oxidation and staling reactions.

Copper that is biologically bound to yeast cell walls can precipitate H₂S and then be removed with finings or filtration. Yeast-based copper products are therefore an ideal solution for H₂S removal without significantly increasing copper levels in the finished beer.

Stay tuned for new sulfur removal solutions from Lallemand Brewing in the near future!