Sour twang with Tripel using WY3787

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Making sales and brewing ales.
Apr 30, 2018
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Springfield, Oregon
8 weeks ago I brewed a Trappist Single using Wyeast 3787 Trappist High Gravity yeast (Westmalle Strain). The single turned out OK--not my favorite beer, but not with noticeable flaws--I primarily brewed it for the slurry.

I pitched roughly half of that slurry into a 1.074 OG Tripel and fermented it from 64 - 72F over a 10 day period, gradually raising the fermentation chamber by a degree or so per day. I then held it at 72F for another 12 days and just took a sample today, on day 22.

It's incredibly tart. Like almost Duchesse d'Bourgogne tart. It finished at 1.011 for an AA of 86%. The grist is 80% Pilsner, 15% table sugar, 2.5% wheat malt, 2.5% aromatic malt. The pH of the finished beer is 4.05. I hit a mash pH of 5.2-5.3, IIRC.

I've not had much luck with 3787 in the past, and have had one other experience with a Tripel using this yeast that tasted seemingly infected/super sour. I'm not sure that's the case here, but I am confused why this happened. There are no pellicles in the fermenter that I can see.

What could cause this beer to get so dang tart?

Water (RO built up to the following profile):

CA 64

MG 8

SO4 50

MG 6

CL 100

HCO3 0

My dilemma is that I have accumulated heavy Belgian glass over the past 4 years to complete this series of Trappist-inspired beers, and would hate to use 50 of my 110ish remaining bottles packaging up a beer that might always drink like fresh squeezed lemon juice.

I also still have a pint of slurry that I was planning to use in a Quad/Dark Strong, but if it turns out tart like this I'd probably cry/scream/throw my fermenter away.

What's your take on why this happened, and where the problem lies? Is this typical for stronger 3787 beers early into their lives?
Sounds like a contamination issue. This yeast does not generate significant acidity on its own. Somewhere between your first batch and the second, the yeast slurry picked up Lacto or some other bacteria or wild critter. If sour beers are not your thing, get rid of the yeast and start over, and better luck next time.
Thanks for the response. I'll dump the beer as well as the slurry I have in the fridge.

Man, what a bummer. Thinking back, I've had three Tripels turn out this way--two with Wy3787 and one with WY3522 Ardennes. Probably coincidence--and the other 3787 had pellicles all over it--but it seems like the universe does not want me to make this beer. I will pick up a fresh smack pack and build a big starter for the tripel, split some off and build a second starter from that bit for the quad. And my fermzillas will also get the bleach treatment just to rule out it happening again.