Banana Beer again! What to do?

My AG ale has that banana thing again. I think it is diacetyl. I'm pretty sure I pitched an adequate amount of quality yeast (made a starter of WLP-005, had good activity early on, calculated attenuation at 72%). Grain bill was 6# 2-row, 2# Light Munich and 1/2# carapils from which I calculated 29 ppg extraction. Mash temp was 150 for 1 hour. Added 1# of honey during the boil. Hop schedule was 1 oz of Nugget at start and 1/2 oz Cascade last five minutes. Left it in primary (closed bucket) for two weeks, then bottled some and kegged the rest. Opened a bottle after 1 1/2 weeks and noticed the banana. Waited another week, then tried the first sample from the keg- same thing.

I don't try to control my fermentation temperature, but my basement in Michigan this time of year is not over 70. When this batch was fermenting (late October) it was probably 65 or so.

I've had this before, but not always. Can anyone tell me what the culprit is?

Thanks in advance.

Has a monkey or family of monkeys had access to your basement in the last six months?

No, but this might attract them. So far only a few mice who really like malted barley when they can get it.

Diacetyl generally isn't a problem with ale yeast. That banana flavor is a fermentation temp issue caused by the yeast. Try keeping those ferm temps below 68...that's the beer temp, not ambient.

Try monitoring the temperatures of your brew. If you can, try to keep the temperatures below 65°. You may also want to try a different strain of yeast, since that is likely where you are getting the banana flavors from. I also read a tip in another thread (can't remember which one) to put boiled bread yeast in the primary to absorb toxins and other impurities that might affect the yeast.

You should give it more time in the primary. Taste it before you bottle. Some diacetyl will always be produced, but giving it at least a few days after fermentation is complete should clean it up. Again, taste it before you rack it off the yeast. If it tastes estery or buttery or whatever, give it more time. Also, this strain has high floculation, which could mean that the yeast are settling out before fermenting completely and removing the diacetyl. Next time, try rousing the yeast when the gravity gets near expected FG.

Thanks all for the responses. How do most homebrewers control the temperature of the fermentation?

gkeusch said:

Thanks all for the responses. How do most homebrewers control the temperature of the fermentation?

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Aside from refrigeration with a thermostat, you can use a water bath, which works very well. I've been able to achieve temp control within 2-3 degrees with it. Get a big receptacle large enough for your ferment vessel and water. I use a 20 gallon pot. Others use a big plastic storage container. Put your ferment vessel in, fill it with water, then use plastic 2-liter bottles of soda filled with water and frozen to keep the temp of the water down. Two of those bottles in my 20 gallon pot is plenty to keep temps down. In any case, the water is what buffers temp swings, acting as thermal mass.

Most of my banana beers have cleared up after a few weeks in the bottle. I have chalked it up to being too green. I second the comment about ferment temps, but I wouldn't expect that until you are hitting the mid-70's.

I had this issue once, but it wasn't with the whole batch. I had one bottle that wasn't completely full that I had sitting in the fridge for a few months. the rest of the batch was great, I just never opened this bottle because it wasn't a full bottle. Maybe 3/4 full. When I did finally decide to finish that bottle.....big time banana flavor. I was puzzled as all the other bottles didn't have that flavor and were very enjoyable. oops, sounds like I'm trying to hijack the thread...just saying...it happens. Just didnt have it happen to the whole batch. I posted this before myself, didnt get much response so I'm assuming everyone was as puzzled as me.

"Banana" flavor and aroma is a flavor called "esters".

"Diacetyl" is buttery, or slick, or oily.

It sounds like you have esters, from a too-warm fermentation temperature, not not diacetyl at all.

I agree, temp is the likely culprit. Isn't all british and english yeast likely to produce more diacetyl than other strains? How old was the yeast you used to create the starter? How long did you propagate the yeast?

I used a first generation slant that was about 9 months old. It still looked good and worked OK, but I was wondering if the shelf life would be any kind of factor.

If you made the appropriate sized starter, the age of the yeast shouldn't really matter as the yeast responded for you properly. BTW, you still haven't mentioned the strain Some strains are notorious for producing banana esters, especially at higher ferm temps!

I agree with everyone that recommended taking control of your fermentation temperatures for every batch you brew. Even the most clean fermenting strains will produce unwanted off flavors at extremes of their range. You can brew two identical beers and use the exact same yeast but if you ferment one at say, 62 and the other at 70 you would be hard pressed to know they were the exact same beers

grimstuff said:

Aside from refrigeration with a thermostat, you can use a water bath, which works very well. I've been able to achieve temp control within 2-3 degrees with it. Get a big receptacle large enough for your ferment vessel and water. I use a 20 gallon pot. Others use a big plastic storage container. Put your ferment vessel in, fill it with water, then use plastic 2-liter bottles of soda filled with water and frozen to keep the temp of the water down. Two of those bottles in my 20 gallon pot is plenty to keep temps down. In any case, the water is what buffers temp swings, acting as thermal mass.

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I've used this procedure many times with great success. One thing I do is put a cap full of bleach in the water to keep anything from growing in the water while it sits for three weeks and make sure to dip a towel in the water and then wrap it around the carboy or bucket and that will wick the cool water up the towel and keep the whole thing cooler.

It is best to chill the wort down to 60F or lower before pitching. It is (nearly) impossible to cool fermenting beer.

The fermenting beer will likely be 5 or 6 degrees higher than ambient temps.

ONLY banana beer I had was fermented too high. I learned quick. Slow and Low is best.

Thanks again, all. Clearly it's esters and a result of too high a fermentation temp. I will fix that next time. By the way, does the fermentation process itself produce heat (let's see - exothermic?) that adds to the problem?
I bet I'm opening up a can of worms here...

gkeusch said:

Thanks again, all. Clearly it's esters and a result of too high a fermentation temp. I will fix that next time. By the way, does the fermentation process itself produce heat (let's see - exothermic?) that adds to the problem?
I bet I'm opening up a can of worms here...

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Yes! could be anywhere from 5-10 degrees depending on how active it is.

gkeusch said:

Thanks again, all. Clearly it's esters and a result of too high a fermentation temp. I will fix that next time. By the way, does the fermentation process itself produce heat (let's see - exothermic?) that adds to the problem?
I bet I'm opening up a can of worms here...

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No can of worms... fermentation produces heat, simple as that. If you're exerting cooling on the beer somehow (like in a water bath), it might suddenly drop the temp a bit too far once that primary fermentation is done because the yeast are slowing down. You don't want that. Try to maintain the actual beer temp at the same level for a few days after you've reached your FG in order to help get rid of unwanted flavor compounds. Taste it and take a gravity reading. Calculate percent change in gravity (i.e. attenuation) and compare to typical attenuation for the yeast strain you're using. If it's not done, rouse the yeast and maybe warm it a few degrees. Yeast strains that have med-high flocculation are at additional risk of slowing or stopping before they're done.

Specifically it's an ester called iso-amyl acetate.

British yeasts typically give you a beer with more esters, though not always banana character. Temp control will help for sure, but if you prefer a more neutral yeast character with less esters, try some of the less estery strains like 1056, 1272 (has some but not like Brits), 1728, etc, or their White Labs equivalents.

Most Brit yeasts fermented at 63-65 or so shouldn't have this at an elevated level. As others pointed out, that's the temp of the beer, not ambient temp. Beer will warm up much higher than ambient during fermentation.

I had a few banana bombs, like some like to call them, before I got fermentation temperature under control. My beers turned out much better once I got a dedicated fermenting fridge with temperature control. With my setup, the wort/beer is always 4 degrees warmer than the thermostat, so I can control the fermentation temperature pretty well. I get more ester production when I ferment warmer or when I pitch the yeast warm then cool it down. Some strains of yeast produce more esters/phenols than others, but controlling the pitch rate, pitch temp, and fermentation temp changes the flavor character of the yeast. So I suggest picking a clean fermenting yeast and look at controlling those three things.

It also seems like you are trying your beer while it's still a little young. If you had it in primary for 2 weeks then bottled and kegged, from my experience, I would expect the flavor to be best sometime after three or four weeks. I typically ferment my medium gravity ales 10-20 days, bottle, and let them sit for over 3 weeks. I can drink my IPA's earlier because all that hop flavor and aroma masks most other flavors, but for more balanced beers, it takes some time for the flavors to come together well. Considering you may have off flavors from fermenting warm, and your beer will need even more time to condition.

MattHollingsworth said:

Specifically it's an ester called iso-amyl acetate.

British yeasts typically give you a beer with more esters, though not always banana character. Temp control will help for sure, but if you prefer a more neutral yeast character with less esters, try some of the less estery strains like 1056, 1272 (has some but not like Brits), 1728, etc, or their White Labs equivalents.

Most Brit yeasts fermented at 63-65 or so shouldn't have this at an elevated level. As others pointed out, that's the temp of the beer, not ambient temp. Beer will warm up much higher than ambient during fermentation.

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Thank you - very informative and helpful - Even more cool that you are in Croatia! If you are a US Serviceman, thank you twice!

gkeusch said:

Thank you - very informative and helpful - Even more cool that you are in Croatia! If you are a US Serviceman, thank you twice!

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You're welcome, though I'm not military. Just an expat living here.

Age of the yeast does matter. If you are starting with a very old sample of yeast and growing it up for only a day, you've only increased a small number of cells by 20%. This is based on recent research from White Labs. The duration of starters matter.

I made an AG Imperial Stout, and used the second runnings to make a "porter". Both used WLP-002 which is similar to the WLP-005. In my Michigan basement, temp was around 68 degrees.

I put the IS in a water bath - glass carboy sitting in a tub of water to help regulate the temperature and provide a thermal mass to get rid of the fermentation heat. I was not able to do this with the "porter".

I when it came time to put the IS in secondary, it tasted amazing. Smooth, roasty, full bodied - everything I hoped for and more. No esters that I could pick up and I was looking for them, because I was kind of worried about my fermentation temps.

The "porter" didn't go into secondary, it went straight to bottling. I almost didn't bottle it because it was almost like a Red Stripe, if you ground up bananas and put it in a Red Stripe bottle. But I figured I might as well bottle it since everything was ready. Two weeks out, it was pretty bad. Four weeks out, getting better... It's been over three months now and I've gone through about half the batch and wish I hadn't gone through that much. It's getting much better with age. Just let it sit and chill and it will probably get better with time.

I am all but certain that the porter's internal temp was well above the ambient temperature in the basement and that this was the source of my esters. I unintentionally did a side by side test

You may want to check out https://www.homebrewtalk.com/f39/never-dump-your-beer-patience-virtue-time-heals-all-things-even-beer-73254/ for a short novel from Revvy on the subject - it matches my experience. Don't give up on your beer!

Thanks for that! I've still got a dozen bottles and I am going to wait until Christmas to try one (the stuff in the keg is still banana-ey, but not un-drinkable). The interesting thing is, when I started this post I already had my "Christmas Stout" sitting about four days along in the primary in almost identical conditions to the ones of my previous brew that caused my post. After you all helped me figure out that it was ferm. temp. I got it in a water bath...will be interesting to see if the esters are noticeable in that one.

This is a great forum...