Forced Ferment - Higher Gravity/Lower pH Than Actual Beer?

[brewinginct]

I just tried doing a force fermentation test on my last batch (a saison) - I poured a sample of wort into the flask that I had made my yeast starter in, so there should have been sufficient yeast for the sample.

I left the sample out at room temp (~62F) for four days. For reference, the actual beer has been fermenting at 73F (it's a saison).

Four days into primary, I took readings on the sample.

• Gravity was 1.015
• pH was 3.97
• Sample was crystal clear

It tasted a little tart, maybe a flavor that could be described as funk.

Compare this to the readings I just took from the beer in the fermenter:

• Gravity is 1.007
• pH is 4.11
• You cannot see through the sample

The sample tasted just as I expected it to. This is definitely still fermenting, though.

I was surprised by how clear the beer dropped in the forced ferment sample - even when i cold crash this beer, it usually has a straw-colored haze, similar to a hefeweizen.

What's throwing me off is the difference in gravity. The pH and flavor/aroma of the forced ferment sample leads me to believe that it may have been infected. Yet, if it were infected, how could it have a higher pH than the actual batch of beer, which has a lower gravity and a higher pH?

 

[user 141939]

I'm confused. Your forced fermentation was done at a lower temp than the actual beer? This seems like the opposite of what you would want to do. And why are you even doing it? Usually I thought this was done for lagering.

And if you put wort in the flask your starter was in, what Yeast was in there? Wouldn't you have poured the yeast from your starter into your beer? Or did you just leave a little in the flask for your test?

 

[brewinginct]

I let the batch of beer that I'm fermenting free rise to the 70s. The larger batch has enough thermal mass that it's staying above room temperature, but the sample in the flask was so small that it probably stayed at ambient, in the mid-low 60s. I made an extra-large starter so that there would be some leftover for this sample.

Besides lagers, another reason to do this test is general quality control. If you force ferment your beer and it stops at X, then that should be the lowest gravity your beer can hit with brewers yeast. If your batch ends up at a lower or higher gravity, then that might be indicative of a problem somewhere in the brewhouse. Or maybe not, I'm hoping someone can clarify!

 

[user 141939]

Makes more sense now. I have no idea why the differences though. Never bothered to do that, even with lagers. I kind of would not be surprised that they would be different. Just since the fermentations are quite different from eachother.

 

[trentm]

I was surprised by how clear the beer dropped in the forced ferment sample - even when i cold crash this beer, it usually has a straw-colored haze, similar to a hefeweizen.

What's throwing me off is the difference in gravity. The pH and flavor/aroma of the forced ferment sample leads me to believe that it may have been infected. Yet, if it were infected, how could it have a higher pH than the actual batch of beer, which has a lower gravity and a higher pH?

Interesting! While I can't argue with the taste, I sort of doubt the sample was infected. If it were infected with Brett or other wild yeast, it certainly would not have cleared. If it were infected with an LAB, the pH may have been much lower. My guess is the yeast may have pooped out due to low temp. Some Belgian strains just can't handle cool temps. FWIW; In my experience with forced ferments, the FG will be a little below the batch.