Buttery off flavor / diacetyl.. Troubleshooting

[Allyster]

Everything was perfect during the brew day. Tasted when I checked FG and the beer tasted great, minimal O2 exposure. When I went to bottle, I tasted a slight buttery flavor, and a slickness to the tongue. I thought it may be the Motueka hops as it was my first time using it.

Cracked a bottle 1 week into carb to see if the flavor lingered, and I still noticed it.

I kept a temperature of 20C, may dip lower at night, but that was the set temperature.
Any thoughts?

 

[Tobor_8thMan]

I was going to write about Pils malt and DMS, but since OP wrote about "buttery flavor" I'm writing the following.

Diacetyl
Tastes/Smells Like: Butter, Rancid Butter, Butterscotch, Slickness in the mouth and tongue.

Possible Causes:
Diacetyl is naturally produced by all yeast during fermentation and is then “reabsorbed” by yeast cells. Increased diacetyl or diacetyl that is not reabsorbed may be a result of high flocculating yeast, weak or mutated yeast, over or under oxygenating, low fermentation temperatures and weak or short boils. It is generally regarded as a flaw when detected in lagers. Some brewers, and drinkers alike, desire small amounts in ales.

How to Avoid:
Taking the following steps will help yeast to properly reabsorb diacetyl in wort: Yeast that is highly flocculant may fall out of suspension before it gets a chance to absorb the diacetyl, using medium flocculation yeast should give the yeast a good chance to absorb diacetyl. Always use high quality yeast and avoid weak or possibly mutated strands that may be incapable of handling diacetyl properly. Allow yeast to begin initial growth with the use of a yeast starter. Supply sufficient oxygen for yeast growth,
but avoid over oxygenating especially after pitching yeast. Allow enough time for yeast to fully ferment at appropriate temperatures.

 

[dbsmith]

How long did you let it ferment before bottling? I looked at a diacetyl curve graph several years ago, and if I remember correctly, I saw a good dip occurred after 12 days or so at typical ale temperatures. For this reason, I always ferment for at least 2 weeks before bottling.

 

[VikeMan]

Diacetyl is naturally produced by all yeast during fermentation and is then “reabsorbed” by yeast cells.

Actually, yeast don't produce diacetyl. They do produce α-acetolactate, which is leaked into the beer. Once in the beer, much of it is oxidized to form diacetyl. I realize it's a sometimes convenient shorthand to talk about diacetyl as being made by yeast.

Increased diacetyl or diacetyl that is not reabsorbed may be a result of high flocculating yeast, weak or mutated yeast, over or under oxygenating, low fermentation temperatures and weak or short boils.

- True, highly flocculant yeast strains do tend to leave more diacetyl unabsorbed.
- Mutated yeast is something I've never heard of in relation to diacetyl. Do you have a scholarly source for that?
- Ditto under-oxygenation. Scholarly source?
- Regarding short boils, I think you're thinking of DMS.

 

[nreed]

Are you sure it’s Diacetyl and not sweetness from using 10% carapils?

 

[RM-MN]

Warm your bottles up to 25 to 28C for a week, then chill just one and sample it to see if the buttery flavor is gone.