I asked this question a while back, and got a lot of good suggestions. But they didn't fix the problem.

My most recent batch is a witbier. It started at 1.050 and started fermenting in 12 hours. The airlock bubbled rapidly for five days and then stopped, even though I raised the temperature to 72F after the third day. After a week I took a gravity sample, and it's still at 1.028.

Based on the advice in the last question, I used a 1.2L starter this time and aerated my wort with an aquarium pump for 20min before I pitched.

Witbier recipe (5gal batch): 7lb Pilsner, 5lb flaked wheat. Mashed for 60min at 153F, temp dropped to 152F by the end. Wyeast 3944. RO water with 3g of CaCl2 and 3g of CaSO4.

I never had this problem in my first 10 batches. Why might it be happening now?

  • What is the FG that you expect to get? – Philippe Jun 26 '18 at 15:34
  • My recipe calculator predicts 1.011. – Josh Yeager Jun 26 '18 at 18:16
  • Did you cross-reference your mash temperature with a different thermometer, or calibrate your thermometer to ensure that it's accurate? – David Liam Clayton Jun 26 '18 at 19:03
  • Also, did any of your previous batches have such a large unmalted component to the grain bill? – David Liam Clayton Jun 26 '18 at 20:13
  • Yes, I've calibrated my thermometers, and they're accurate. I haven't brewed with this much unmalted grain before, so I think the problem is independent of the malt bill. – Josh Yeager Jun 26 '18 at 20:32

Given the normal lag time, your wort aeration and the yeast starter, we may assume that you've got a proper yeast culture pitched into well oxygenated wort. RO water (even with your additions) is not ideal and you could possibly do with some yeast nutrient supplementing your salts, but your malt should take care of some of that, and in any case it's not a typical cause of what you describe here. In short, I think we can pretty much rule out oxygen, yeast, water and nutrients. Which leaves wort composition.

The only suspect I can think of is the flaked wheat. A grain bill of 7lb Pilsener malt and 5lb wheat malt is a decent one for a witbier, but I'm not so sure about the flaked wheat.

Firstly, while wheat malt usually has some diastatic power (not all that much, but still) flaked wheat has none at all.

Secondly, not all flaked wheats are created equal. Depending on how much heat the wheat has been exposed to during processing (and for how long) the degree of gelatinization may vary. Some flaked wheats are steamed and then rolled (compressed) while other are mostly just shredded and are supposed to be cooked.

If your flaked wheat is the latter (i.e. it has been processed relatively cool and quickly) the bulk of the starches are likelely not pre-gelatinized at all, which means you've now dumped a ton and a half of insoluble starch into your mash tun, with which the enzymes from the Pilsener malt can do little or nothing.

If you cereal mash the flaked wheat and repeat the brew with better results, you have isolated the problem.

  • Thanks. I'll try that next time. But I don't think this problem is caused by my grain bill, because the same problem has happened with several other recipes that didn't contain wheat. – Josh Yeager Jun 28 '18 at 14:21
  • If it's not your wort composition and it's not aeration (assuming you use a bubbler stone), it's either the yeast (which seems unlikely if you managed to grow it up properly in a starter) or the water. Maybe the yeast is missing some essential nutrient. Try adding a good yeast nutrient, try using different water. If that doesn't work, try pitching several vials of yeast not grown in a starter. Change one variable at a time. You should get some good hints as to where the problem originates. – Frank van Wensveen Jun 30 '18 at 7:27
  • It seems like the flaked wheat was probably the cause of this batch's high FG. I roused the yeast twice and left it for two more weeks, and the gravity is very stable at 1.021. It tastes a bit too sweet, but that might just be because it's not carbonated yet. I'm going to bottle it and see how it turns out. – Josh Yeager Jul 13 '18 at 15:23

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