Diacetyl questions.

I have issues with my beer ending to have a diacetyl smell.

My first batch ever, fermented with US-05 was turning ok until I bottle conditioned it in a very cold temperature.
Primary fermentation - 2 weeks
Secondary - 2 weeks

Second batch was a Saison that came out fine.
Primary - 3 weeks
Secondary - 1 week

Third has a slight butter flavor but it mingles well with a banana esters.
Primary 3 weeks
No secondary. Bottled Straight.

Forth batch was also fermented US-05 and it was turning really fine after 3 weeks fermenting and then a week of secondary.

I suspect that when adding priming sugars there isn't enough yeast to work through it and the diacetyl stays.

Or while transferring the beer from one fermenter to another and then to bottling bucket I oxygenate it too much ?

I have 2 Saisons in the secondary that I have to bottle in couple of days. I start to worry I will have the same issues with diacetyl too.

Both Saisons are tasting perfect now. I don't sense any oily or diacetyl. They stayed 3 weeks in the fermenter so I'm sure of it.

Any suggestions ?

My first suggestion is to leave your beers in primary for 3 to 4 weeks and not rack to secondary. Racking to secondary removes the beer from the yeast. You want all the yeast you can get to clean up after their party.

Diactyl is a buttery or butterscotch taste. Usually this happens with lagers which is why it is good to do a d-rest where the temp is raised at the end of fermentation (right when the yeast are 75% done). US-05 is an ale yeast so fermentation should have been in the 60s. You should really get diactyl from that. US-05 cleans up really nicely.

Oxidized beer will have a cardboard flavor to it. Diactyl buttery flavor and oxidized cardboard flavor aren't two things that would happen because of one problem.

If you do not do so already hydrate your dry yeast prior to pitching to get the yeast more active.

Also make sure you are aerating vigorously. You can do this by shaking your carboy for about 40 seconds as per wyeast labs expirment.

As previously mentioned, secondary isn't really necessary in most cases. The yeast are still working, and the more the merrier!

Most likely, you're under pitching or not aerating enough.


Have you considered the fact that you may have a piece of infected equipment? Maybe something you've used with some batches, but not with others? Plastic bucket? Different tubing? Forgot to sanitize a hydrometer, funnel, or bung?

Yeast have an important job to do, and fighting with little nasties can severely hamper it's cleaning up efforts. It's rare, but some infections can remain almost unnoticed for a while...

"You should really get diactyl from that. US-05 cleans up really nicely."

Do you mean "you shouldn't" ?

So the problem is with priming when the leftover yeast number is too low.

What I'm trying to understand is : yeast is producing diacetyl during the bottle conditioning ? Because after 3 weeks of primary fermentation seams a lot of time for ale yeast to clear all the diacetyl taste. I am suspecting, since the fermentation is reactivated, the yeast cells produce it again ?

k1ngl1ves said:

As previously mentioned, secondary isn't really necessary in most cases. The yeast are still working, and the more the merrier!

Most likely, you're under pitching or not aerating enough.


Have you considered the fact that you may have a piece of infected equipment? Maybe something you've used with some batches, but not with others? Plastic bucket? Different tubing? Forgot to sanitize a hydrometer, funnel, or bung?

Yeast have an important job to do, and fighting with little nasties can severely hamper it's cleaning up efforts. It's rare, but some infections can remain almost unnoticed for a while...

Click to expand...

I exclude the infection for the moment since I take a huge care in sanitizing. But If I run out of other options I will have to consider it somehow.

When it comes to pitching I always use more yeast then necessary. That was one of the first advises I got from a guy working in the homebrewer shop. I don't rehydrate it since I was told that even though some cells might die, the final will be the same (I was told).

Even if I under pitched it the diacetyl should be present while tasting the beer during the primary right ?

My beers never tasted diacetyl. Not until I open the bottle.

Swaroga said:

So the problem is with priming when the leftover yeast number is too low.

What I'm trying to understand is : yeast is producing diacetyl during the bottle conditioning ? Because after 3 weeks of primary fermentation seams a lot of time for ale yeast to clear all the diacetyl taste. I am suspecting, since the fermentation is reactivated, the yeast cells produce it again ?

Click to expand...

No, yeast activity during bottle conditioning is very minimal. Not enough to produce any noticeable flavor of any kind really.

Swaroga said:

When it comes to pitching I always use more yeast then necessary. That was one of the first advises I got from a guy working in the homebrewer shop. I don't rehydrate it since I was told that even though some cells might die, the final will be the same (I was told).

Click to expand...

If you're not rehydrating you're likely not pitching as much yeast as you think. Like you said, when you don't rehydrate some of the yeast die. People have shown that it can be as much as half of your yeast that dies. What do you mean the final will be the same? The point of pitching the right amount of yeast is so that you will start with the right amount. It doesn't matter how much you have at the end of fermentation.

Swaroga said:

Even if I under pitched it the diacetyl should be present while tasting the beer during the primary right ?

My beers never tasted diacetyl. Not until I open the bottle.

Click to expand...

Are you sure it's diacetyl you're tasting? People say cardboard for oxidation, but I've always tasted it as a sweeter sherry type taste. Have you for sure tasted diacetyl before?

What are your fermentation temperatures? Since your saison doesn't have this flavor it makes me think it might be due to too high fermentation temps.

Swaroga said:

Even if I under pitched it the diacetyl should be present while tasting the beer during the primary right ?

My beers never tasted diacetyl. Not until I open the bottle.

Click to expand...

There is a taste threshold for diacetyl. In certain beers, it is hard to distinguish even when double the threshold. (I don't remember the numbers, so don't ask. ) It also gets worse over time, which would be why you get a "Surprise!" when you open a bottle down the road...

Echoing PeterJ, are you sure it's diacetyl? Take it to your LHBS and find out. Most ales finish fermenting in 4-5 days, or sooner. Plenty of people will tell you to leave the beer on the yeast for 3-4 weeks, but the fact is, that's not necessary. After fermentation is complete, the process of cleaning up byproducts (such as diacetyl) takes less than 48 hours. Read Chris White's (of White Labs) book Yeast. He has a PHd in yeast science. He knows what he's talking about.

Many beers benefit from some degree of aging, but that's not diacetyl, and it has nothing to do with whether or not the beer is still sitting on the yeast cake.

What you taste as diacetyl might be crystal malts shining through, or another grain. The only way to know for certain is to have someone who recognizes diacetyl taste it. I made an IPA once with munich malt and carared that I was convinced had diacetyl, and it turns out it was just an overly malty aroma/taste from my grain bill. Once I got over it, the flavor at issue became my favorite and I now strive for it in IPAs.

i'm not sure when you are getting the diacetyl, but i have ABSOLUTELY noticed a STRONG, NEW diacetyl flavor in beer for up to two weeks after bottling. the way i test is that i take a 6-8 oz sample from the bottling bucket, keep it loosely covered, and taste it daily.

it seems to be correlated to those times when i pitch new yeast at bottling (i do this a lot) and it always goes away to nothing after a couple of weeks.

i can't explain it, but i've seen it even in beers that have been maturing for months before bottle conditioning.

It's true that I am completly confused about how exactly tastes diacetyl. My first batch smells a bit buttery but it isn't something that puts me off. I used amber liquid extracts, cara and munich grains. Fom the start I was thinking if it's butter diacetl or butter tart.

In anyways my next brew I will do some new steps :
-rehydrate properly the yeast,
-use longer tubing to avoid oxydetion while transfering,
-hold it longer till 4 weeks in the primary fermentation and skip the secondary.

Thanks a lot people.

Swaroga said:

"You should really get diactyl from that. US-05 cleans up really nicely."

Do you mean "you shouldn't" ?

So the problem is with priming when the leftover yeast number is too low.

What I'm trying to understand is : yeast is producing diacetyl during the bottle conditioning ? Because after 3 weeks of primary fermentation seams a lot of time for ale yeast to clear all the diacetyl taste. I am suspecting, since the fermentation is reactivated, the yeast cells produce it again ?

Click to expand...

Yes I did mean shouldn't. Thanks for picking that up.