Delayed Off Taste

[Ewalters]

I recently kegged a German Pilsner that I pressure fermented. For the first week or so after it was carbonated it tasted great but recently it has developed this almost maple syrup off taste. I close transfer and am fairly militant about sanitation. Anyone ever taste something similar?

The taste is not overwhelming and only on the back end of each sip, but I can’t pin point what it is.

 

[VikeMan]

Almost maple syrup.... is it at all close to a caramelly or butterscotch flavor?

 

[Yooper]

I recently kegged a German Pilsner that I pressure fermented. For the first week or so after it was carbonated it tasted great but recently it has developed this almost maple syrup off taste. I close transfer and am fairly militant about sanitation. Anyone ever taste something similar?

The taste is not overwhelming and only on the back end of each sip, but I can’t pin point what it is.

Any color change at all? I notice a ‘brandy’ like taste in early oxidation in some beers, sort of becoming sweet like brandy.

 

[Ewalters]

Closer to caramelly than butterscotch. I was thinking a disc

Almost maple syrup.... is it at all close to a caramelly or butterscotch flavor?

Of the two more caramel than butterscotch. Almost malty. It does not taste like diacetyl which I’m usually good at picking up. Possibly could be, but whenever I’ve had that it’s been from the onset and not delayed like this.

 

[Ewalters]

Any color change at all? I notice a ‘brandy’ like taste in early oxidation in some beers, sort of becoming sweet like brandy.

No significant color change. The delay of the flavor makes me think it’s an oxidation issue too, but I did purge the keg by filling with starsan to the very top and purging with gas. Then pressure transfer from conical without interruption. The liquid QD was leaking a bit from the top so I wonder if it was letting in oxygen as it transferred.

 

[VikeMan]

Of the two more caramel than butterscotch. Almost malty. It does not taste like diacetyl which I’m usually good at picking up.

Diacetyl can taste different depending on the beer and also depending on the concentration. I wouldn't be too surprised if diacetyl is what you're tasting.

Possibly could be, but whenever I’ve had that it’s been from the onset and not delayed like this.

It's a common misconception that yeast makes diacetyl and then cleans it up, so if you don't taste diacetyl at packaging, you're good. Unfortunately, it's more complicated than that.

The yeast actually make diacetyl's precursor, α-acetolactate, which leaks into beer, where it’s subsequently converted to diacetyl by oxidation. But it's not as simple as "make all the precursor, then convert all the precursor to diacetyl, then clean up the diacetyl." The yeast can clean up all the currently available diacetyl (or at least clean it up to below taste thresholds) while there is still unconverted α-acetolactate in the beer. If crashed/kegged at that point, the rest of the α-acetolactate will be oxidized to diacetyl, sometimes bringing it back above taste thresholds.

This is the reason for forced diacetyl tests. Heating a sample of the beer accelerates the conversion (oxidation) of α-acetolactate to diacetyl. If the sample is "clean" after heating, you know there's little/no risk of (detectable) diacetyl forming in the main batch.