Great Plains District

For the last six months we've had a harder time getting good counts and viabilities out of our harvested yeast. To put that in context, we historically would harvest multiple brinks of yeast with counts in the range of 600 million to 1.5 billion cells/mL @ viabilities of 95% +. We now are harvesting the same or fewer number of brinks per tank in the range of 100 million to 800 million cells/mL with viabilities ranging from 70-98% but with the vast majority falling within the high 80's and low 90's. We have not changed any of the procedures (though we have changed sanitation chemical, but the change does not align with the start of our struggles) we have used for the last 6+ years during this time, so I am struggling to figure out what exactly is going on. Our procedure is as follows:

1. Wait until we've hit terminal gravity or are withing a few tenths of a point of terminal to begin cropping
2. If it's an ale yeast drop temp on the tank from ~70 degrees to 65 degrees 24-48 hours before the first crop
3. We dump ~5-10 gallons off the bottom the day before our first crop to remove trub and dead yeast. This is on 40, 60 and 80 bbl tanks.
4. Sanitize the yeast brink night before crop or morning of. We used to use Oxine with no rinse, we stopped being able to get that sanitizer and switched to PAA with rinse. We have recently been experimenting with Star-San with a rinse (yes, I know its a no-rinse sanitizer) just to see if it makes a difference, I had some concern maybe the switch to PAA was straining our yeast in the brink. No noticeable difference thus far.
5. Crop slowly off the bottom. We tend to take 120 lbs of Chico or other ale yeasts and 160 lbs of various Lager yeasts into a 100 L brink. We will break that collection up into two parts, running a slow but steady stream for the first half, then closing up the brink and the tank and letting everything stand for a few hours before returning to collect the second half in an effort to prevent tunneling in the cone.
6. We lay the brink on its side and rock to agitate and homogenize the contents before taking a sample into an autoclaved vessel for counting.
7. We store the brinks in our walk in cooler at ~34 degrees F, and we vent any built up pressure in the brinks daily until use. Except in very unusual circumstances we utilize the stored yeast within 7 days time and typically it really is within 5 days maximum from collection to pitch. As we have started to struggle with harvest yields, that timeline has compressed to pitching within 24 hours of harvesting, which I assumed would have a positive effect on the yeast, but has not seemed to actually end up mattering.
8. We count all of our yeast with a hemocytometer and microscope. We have both a microbiologist for our lab tech, and a trained brew staff member on team to perform counts. Their counts tend to line up with one another, and they both have been doing this procedure for many years, so I don't think counting error is responsible for the change.
9. We attempt to pitch all of our yeast between 750,000 and 3,000,000 cells/ml/degree Plato depending on gravity and style. Most commonly we are pitching at 1 million for ales in the 14-18 Plato OG range, or 1.5 million for lagers in the 10-15 Plato OG range.
10. We oxygenate our beers using a Flow meter on our oxygen stone in knock out line, and collect samples downstream for DO readings with a Mettler DO probe. We calibrate our DO probe weekly, and while the cap is probably pretty close to the end of its lifespan, I have confirmed with our Mettler rep that it is functioning properly and that we have a few more months before we should replace. We oxygenate somewhere between 14  and 18 ppm depending on wort gravity, for 40 minutes of the typically 50-60 minute KO time. If the brew is 4 turns we will oxygenate for the first three turns but not for the last turn. (A four turn day will have about 8-9 hours between the end of the first knock out and the start of the fourth). Otherwise we oxygenate on every knock out.

We have only recently noticed a slight slow down on lager fermentation times, but otherwise our fermentation curves have been very consistent with the curves from prior to the start of our harvesting issues. Beer centrifuges bright and clean, and sensory tests confirm beers remain true to brand. We order our new pitches of yeast from trusted providers, Omega, BSI, Imperial whom we have utilized for years and have never had issues with in the past. During this period of struggle we have rotated those three suppliers to rule out a supply issue, and we see the same poor harvests regardless of lab we order from, meaning it has to be something we are doing wrong. We see roughly the same issues on harvesting a 1st gen yeast as we do in harvesting a 10th gen yeast. We have recently started to wonder if malt could be an issue and I am collecting wort samples this week to send in for FAN testing just to rule it out.

Aside from a possible FAN issue, at this point I am at a bit of a loss for how to return us to our previous success. Has anyone had anything like this happen to them before? Does anyone see an obvious or glaring error in our process that could be to blame?

Thanks in advance for any advice or suggestions! 

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Joshua Maxson
Confluence Brewing Company
Des Moines IA
(319) 400-9678
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