Troubleshooting - Sulfur Aroma in Beer

Help! My beer has a sulfury flavour 

Sulfur is typically made by yeast as a response to a low nutrient environment. A byproduct of yeast having to work harder to make their own amino acids is the production of sulfury smells. We recommend adequate wort nutrition and oxygenation, and can help advise you on nutritional needs of specific strains.

Background information about sulfur flavour

A deficiency in the wort of sulfur-containing amino acids (methionine, cysteine, etc) forces the yeast to import sulfate in order to synthesize its own S-containing amino acid building blocks. A byproduct of this activity is the production of SO2 and H2S. However, control of sulfur flavours in yeast is a complicated topic.

There are two common sources of sulfur aroma in beer: 

SO2 - "struck match" aroma is typically indicative of restricted yeast growth. This can be an issue with recurrent yeast repitching. Higher oxygen and higher free amino nitrogen (FAN) typically result in less SO2.

H2S - "farty", "sulfury" aroma can result from underpitching yeast, low FAN, or excessive yeast growth. It is also usually associated with faster ferments.

Troubleshooting questions for Sulfur issues: 

The two key places to look here are yeast pitch rates and wort composition. Hopefully, by answering these questions, we can arrive at a solution:

1. What is your typical pitch rate for repitching? Underpitching can result in sulfur issues. 
2. Did you see this issue in the first generation of yeast? Chronic nutrient deficiency can result in sulfur issues. 
3. What is the wort composition (grain bill, etc)? Nutrient deficiency can result in sulfur issues. 
4. How much trub carryover do you get? Nutrient deficiency can result in sulfur issues. 
5. Is any nutrient besides zinc being added? Nutrient deficiency can result in sulfur issues.

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