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Is it possible to ferment too long? I have a partial mash that I began fermenting on April 24 and I forgot about it until today. Is it possible for it to have fermented too long? What will happen? 

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After about 4 weeks, the yeast will begin to autolyze. When a yeast cell dies, it ruptures - releasing several off-flavors into the beer. When you have a large yeast mass on the bottom of the fermentor, you have a large potential for off-flavors due to autolysis. Some of the off-flavors/aromas include burnt rubber or rotten eggs. It can get really bad if left too long. Also, after a few weeks, most of the protective Co2 will off-gas, leaving the beer vulnerable to contamination from wild yeast, mold, bacteria, etc.

 

If your beer has experienced autolysis, you will know it. Give it a taste. If it tastes like flat beer, it's probably fine. But if it's unpalatable, your yeast may have autolyzed. Never leave beer on the sediment for longer than 3 weeks to prevent autolysis.

 

The only exception to this rule is if you are aging the beer in secondary with a wild yeast, such as Brettanomyces. Brett will eat dead yeast, preventing autolysis.    

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@MRB Josh R, is the rate of autolysis variable by temperature? Meaning, given two fermenters, one at ambient temperatures and one held at a lower temperature within the yeast's preferential temperature range, would the room temperature fermenter have a greater risk of autolysis off flavors?

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15 minutes ago, D Kristof said:

@MRB Josh R, is the rate of autolysis variable by temperature? Meaning, given two fermenters, one at ambient temperatures and one held at a lower temperature within the yeast's preferential temperature range, would the room temperature fermenter have a greater risk of autolysis off flavors?

 

Yes, it is. The warmer it is, the faster autolysis happens. It's also dependent on the yeast's age and strain. Older, stressed yeast will autolyze much sooner than fresh yeast. Repitching yeast from batch to batch can also stress the yeast rendering them more prone to autolysis. And certain strains are more prone to autolysis than others. These strains usually include yeasts that aren't very ABV tolerant.

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1 minute ago, Shrike said:

Best thing to do now is build a still and distill it into 'shine.  :)

 

 

Or put it in a secondary vessel with some Brettanomyces yeast and age it for 6 months. The brett will consume the off-flavors as well as the dead yeast cells. It's also a natural antioxidant and will prevent oxidation. Of course, you'd have to like the funky flavors that brett creates (I know I do). It can be an acquired taste. 

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At the mention of burnt rubber and rotten eggs, I'd be hitting the add to cart button on another couple LBK's, and saying sayonnara to that batch! Lol, I can still hear my mother saying when in doubt throw it out.

 

@rowe0123, however you proceed, in the future you might want to put your batch action schedule in your smartphone, tablet, or computer. It helps me anyway to see what's coming up so i can make sure my inventory is good to go for my next brew day.

 

 

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