Sulfur Odors In Beer
Sulfur odors are mostly produced by lager yeasts, although they are produced by ale yeasts as well. Sufury odors are usually produced about two to three days into the fermentation. Unlike some of the other flavors and aromas that will be reduced by the yeast, sulfur odors can only escape from the beer by diffusion into the atmosphere. Most of these sulfur aromas will disappear within two weeks, but there are times when it may take up to a couple of months for the odors to dissipate. The majority of it is carried off by CO2 produced during fermentation, and the rest will usually dissipate with a few weeks of lagering or aging.
Since some subtle sulfur aroma is a big part of the profile for most lagers, it may be of interest to learn what causes it. Two of the most important factors in the production of sulfur compounds in lagers are pitching rate and wort original gravity. Normally, lower pitching rates and/or high original gravity of the wort will produce more of the sulfur aromas in your beer.
Another factor is yeast nutrient levels in the wort. It seems that worts that are low in the sulfur-containing amino acids will produce more sulfur odors during fermentation. You won't normally run into a wort that is deficient in nutrients when making an all-malt beer. It's when you start adding a lot of adjuncts like corn or rice that you run the risk of having low nutrient levels in your beer. If you are having problems with sulfury aromas in your high adjunct beers, try adding a yeast nutrient to your wort prior to fermentation.
Yeast selection will play a role in the amount of sulfur is produced as well. Each strain has its own character and you must be aware of these traits before deciding which yeast is best for your beer.
for a list of yeast strains and their characteristics, including the amount of sulfur the strains produce.
Yeast autolysis can also produce the sulfury odors of rotten eggs and what is often described as rubbery odors. For the most part, yeast autolysis is not a problem with today's liquid yeast cultures. In earlier times, homebrewers only had dry yeast to ferment their beer with. Dry yeast is already stressed from the drying process plus many didn't rehydrate correctly or at all. For most homebrewers, the problem is not leaving their beer on the yeast so long that autolysis occurs, but not leaving it on the yeast long enough to finish fermenting and cleaning up the byproducts.
There are some bacteria which can produce sulfury odors. If all else has been eliminated, and you are having problems with sulfur compounds which won't age out, look at your sanitation procedures.
If you are going to brew lagers, a subtle but detectable level of sulfur compounds will always be produced. The best thing you can do is be patient. Long lagering periods usually mellow the sulfury aromas to below threshold levels. But, if you have been patient and given the beer a long cold lagering period and the sulfur compounds are still present, then it is time to look at other things such as yeast strain selection, abnormally low pitching rates due to yeast damage or shock, pitching into a high gravity wort, and low yeast nutrient levels due to high adjunct percentages.
Information for this article was taken in part from Homebrewing Vol. 1 by Al Korzonas and The Home Brewer's Answer Book by Ashton Lewis, columnist for Brew Your Own Magazine.
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