Process and timing to detect a stalled fermenation in order to add more yeast (repitch)

Question

Working with a 1.060 original gravity wort, mashed at 152F, and using the WLP565 Dupont yeast (that is known to stall), when should the brewer investigate if adding a secondary strain of yeast will be required? Is there a rule of thumb or accepted practice that suggests if X% of expected attenuation is not complete by Y days, then attenuation will very likely require a very long time?

Of course there are various options for the brewer, such as raising the fermentation temperature, removing back pressure, or simply waiting for the fermentation rate to start again. But this question is about the earliest point where the brewer might know with reasonable certainty that action is going to be required to get the beer to quickly completely attenuate, and what to do at that point.

The default process is to take multiple gravity readings, and when the slope doesn't change from one measurement to the next, then it's time to take action. But is there a way to "know", right away, by taking just one, properly timed measurement?

With this yeast, there are many brewers reporting "stuck at 1.030" or "stalled at 1.035", which are roughly only 50% or 60% of expected attenuation, but it's usually after a few weeks of frustration and multiple measurements.

Given that in a typical fermentation curve, the majority of the attenuation occurs in the first six days, when should I take the measurement that will indicate a stall, and above what value would indicate a stall?

Answer 1

The Dupont strain is a kinda special beast. We found in an experiment on Experimental Brewing that you need to open ferment it to prevent the stall. Whether it's pressure or CO2 toxicity hasn't been determined. Assuming you're using an airlock, remove it and use a piece if foil loosely over your fermenter. That should fix it.

https://www.experimentalbrew.com/experiments/saison-yeast-airlock-vs-open-ferment-does-it-prevent-stall

https://www.experimentalbrew.com/podcast/episode-18-saison-under-pressure

To answer your question more directly, though, no, there is no formula for how much attenuation to expect by a certain time. If you want to have an idea of how far the wort might possibly ferment, a forced ferment test is very useful.

Answer 2

In my experience yeast gives up early when I see it drop out of high krausen / exponential growth / feeding phases in 1-2 days. It's the first sign for me to be diligent in taking readings and making adjustments to keep it going well. There's many reasons why this effects final gravity.

Over all its speculated that when the yeast works too fast in growth phase that cell division leaves too many bud scars for the yeast to take up complex large molecule sugars easily.

Also the abv increases faster that the yeast can strengthen its cell walls, and basically poisons its self.

Now I've had very fast primary fermentation without any issues, but this is always when I've done a full pitch of yeast and there's no growth needed to complete fermentation.