Stinky Lagers
TroubleShooting
Francisco Jones - Kankakee, Illinois asks,
My lagers always contain a lot of sulfur (like garbage or rotting vegetation) aromas. My boils are typically 75 minutes, full rolling boils uncovered with overhead vent fan using gas plus electric heat stick augmentation. I use both liquid yeast with stirred starters and dry yeast (all style-appropriate lager yeasts), all scaled to appropriate pitching rates using the calculator at mrmalty.com. Typically I chill to 50 °F (10 °C) and pitch. Then I ferment around 52 °F (11°C) in a dedicated ferment chamber with external temperature control, proxy thermo-well in a separate jug of water, and forced air convection until fermentation slows, and a sample shows about 65-75% complete. Then I raise the temperature over a couple days to about 65 °F (18 °C) and let it sit for a while. I have read a warmer fermentation at the end helps scrub sulfur and absorb diacetyl. My diacetyl is getting cleaned up, but not the sulfur.
Francisco, nothing in your description of your lager brewing throws up any warning flags related to sulfur production. It really sounds like you are doing a very good job with yeast pitching control and fermentation temperature control. The Mr. Malty yeast calculator is a nice tool and is fairly conservative, so I do not think your problem is yeast pitching rate, the root cause of many fermentation off-flavors.
Another key factor related to fermentation-related aromas is yeast strain. It is certainly true with lager yeasts that some strains do indeed produce more sulfur aromas than others. I have used several lager strains over the past 16 years at Springfield Brewing Company and settled on the Augustiner lager strain a couple of years ago and have been very happy with the results. One of the aromas I wanted to minimize in our lagers was hydrogen sulfide, which smells like a rotten egg. The Augustiner strain does produce sulfur during fermentation, but it dissipates in our process to yield very clean lagers.
For what it is worth, we cool our wort to 50 °F (10 °C) and ferment at 54 °F (12 °C). We use a spunding valve, a type of pressure relief valve commonly used to capture carbon dioxide in fermentation vessels, and the valve is put on the fermenter when we are about 1 °Plato above our projected terminal gravity. The beer is held at fermentation temperature for four days after spunding for diacetyl reduction. We then chill the beer to 38 °F (4 °C) and hold at this temperature for about 10 days. The lager yeast is still active at this temperature and diacetyl and acetaldehyde reduction continues during this time period. The beer is then cooled to 30 °F (-1 °C) for at least two days before filtration or racking in the case of unfiltered lagers.
Like many brewers, I have some rituals that are based on a mixture of tradition, practical experience and science. What we do works for us, so we are not real keen on changing things. We cannot raise our temperature for a diacetyl rest, so we use a longer rest period to achieve our goals. I know from pulling samples during lagering that the sulfur profile of our lagers does significantly change during the time from spunding to serving. I have always believed that the slow, continuous release of carbon dioxide from the spunding valve during lagering helps scrub sulfur from the aging lager. One confirmation of this scrubbing is the aroma released from the valve; at the early stages of lagering the sulfur intensity is greater than it is towards the end. If you simply complete fermentation and keg or bottle your lager without this gas scrubbing process there is no mechanism for sulfur removal since yeast does not absorb these compounds as is the case with diacetyl and acetaldehyde. Homebrewers who keg their beer can scrub sulfur compounds by bubbling carbon dioxide into the beer from the spear, then slowly releasing the head pressure, and repeating the process several times. This not only will help to scrub sulfur aromas out of the beer, it is also part of the force carbonation process.
The aromas you describe could be associated with very high levels of dimethyl sulfide. It sounds like you have a very good boil, but if you do not quickly cool wort after boiling, residual S-methylmethionine (also called DMS precursor or DMS-P) will be converted in the hot wort to DMS. In the absence of boiling and steam stripping, the DMS will remain in your wort and can show up as a flavor defect in the finished beer. Most brewers using some sort of wort chiller to cool the wort fairly quickly after boiling do not have this particular problem. My gut feeling is that DMS is not your problem.
Two other things to consider are yeast nutrients and sanitation. While all-malt beers typically contain plenty of amino acids and phosphates, they can be deficient in zinc. Some yeast nutrients, especially types common to winemaking, are mainly comprised of amino acids and phosphates, and other nutrients are really designed to boost zinc levels in wort. We use Servomyces in all of our beers and I believe that this really helps us with producing very clean beers. This product is sold by White Labs and is a good source of zinc. Remember that aeration is important because oxygen is also a sort of nutrient and is integral to the synthesis of membranes during cell growth. Finally, poor sanitation can lead to microbiological issues that certainly can cause terrible off-flavors associated with bacterial contamination. Hopefully I have touched on something to help you produce better lager beers!
