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Home Brew Forums > Home Brewing Beer > Fermentation & Yeast > Tainted batches - what is wrong?
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Old 06-25-2013, 09:54 PM   #31
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You guys might be right about the temp calibration. I am using a stainless thermowell with the probe at the bottom of it. I will calibrate the temp controller and get back with the results of that.


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Old 06-25-2013, 09:56 PM   #32
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Where do you measure the temps you mentioned? On the fermenter? Ambient air?

What yeast(s) did you use on the batches that had the bad flavors? Some yeasts (like Nottingham and sometimes S-04) get nasty above 68*F (measured on the bucket).


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Old 06-27-2013, 09:37 PM   #33
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Update:

So, I went out to take a quick temperature comparison with the thermometer that I THOUGHT was calibrated... I calibrated it with boiling water and it was good. However, at the lower end, I think it might be off. In a cup of warm water, it read 95F when the temp probe read 90. At first I thought, "yes, there is my problem". However, I checked it against a digital meat thermometer AND a digital medical thermometer, and both read the same as the temp probe. So, if three out of four thermometers read similarly, I am lead to believe that my analog thermometer is off by 5 degrees. Let me know if this seems like it's too far a stretch.
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Old 06-27-2013, 10:02 PM   #34
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put them all in boiling water and see if they read 212 too. seems like you might be right though...
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Old 06-27-2013, 10:09 PM   #35
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Sounds like the issue but also check it in ice water at the low end as well. 5 degrees is a pretty big discrepancy.
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Old 06-27-2013, 10:28 PM   #36
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Checked against boiling water, and they all read the same, so on the high end everything looks good. Checked against ice water, everything reads the same as well, and accurate. For whatever reason, the analog thermometer is way off between 70 and 100 or so. Checked the digital meat thermometer against the probe and they are less than a degree from each other.

I was thinking about something, let me know if this sounds off... with the mass of the fermenter, and the probe being about halfway down and halfway in (half the distance from the center and outside wall), is it possible that the fermenting wort is warming enough on the outside of the fermenter and allowing the conditions for too high of fermentation temperatures? The A/C unit only kicks on when the probe gets to the right temperature, but the ambient air is warmer than the mass of the container usually, until the a/c runs. The entire thing is insulated, and stays rather cool, so I don't know.

On the next batch I am going to aim for the very lowest temp that the yeast will tolerate and see what happens...
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Old 06-27-2013, 10:59 PM   #37
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Analog thermometers can take a bit to adjust IME.

I doubt the wort would have that large a temp swing from one location to another in the vessel, it's not going to swing that quickly as its a pretty good insulator by itself, think swamp cooler and the insulation that provides.

I would try the lower end next time as well and see how it goes.
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Old 12-13-2013, 12:10 AM   #38
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I owe a follow up to this thread. Since the last update, I have dropped the fermentation chamber temp to 65 and have had zero issues. The saison mellowed out and was actually a favorite of mine and of everyone who drank it. The best bitter that I made has mellowed out a lot, but there is still a hint of off flavor that makes it not the greatest thing to drink, especially with other great beers available. I think temperature was definitely the issue.
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Old 12-14-2013, 01:26 AM   #39
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It's nice to see a "what's wrong" thread that ends with some resolution. Congrats. That was my most frequent early error...ferm temps. Now I learn what my yeast likes and it gives me what I like....delicious beer!
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Old 12-14-2013, 03:02 AM   #40
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Banana is an ester called isoamyl acetate. It is formed when isoamyl alcohol combines with acetic acid. While high fermentation temperatures can cause yeast to produce isoamyl acetate, poor health and under-aeration also lead the formation of the ester. With most yeast cultures, isoamyl acetate production is mother nature's way of telling us that the culture experienced stress during fermentation.

Anyway, it is nice to see that there was a happy ending to your problem. I am not that patient. I dislike the taste of isoamyl acetate so much that I do not hesitate to dump batches that show as much as a hint of that ester.


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