Middle of Summer but Froze my Yeast to Death (new chiller)

[micraftbeer]

I just got a new chiller and I'm testing it out. Previously I used a cooler filled with 4 gallons of water + five 2-Liter bottles of ice, with a submerged pump. I finally made the change after years of swapping out those 2L bottles in & out of the freezer had worn me down. With that process, I never had an issue of "freezing the yeast out" like I have seen people mention at times. I'm assuming the Chiller was way more capable and hence shocked my yeast and kept them from working. I'm interested to hear other's experiences with this.

Details
- 4.25 gallon of wort
- BrewBuilt X1 Unitank fermentor with spiral cooling coil in the center (coming down from lid).
- OG 1.045
- Added 2 minutes of bottled O2 before yeast pitch
- Pitched yeast in with wort at 72F
- Chiller had glycol tank set to 28F
- Wort chilled to 51F in 5.5 hours
- Wyeast 2206 Bavarian Lager smack pack was starting to swell before pitched (probably would've done a small starter, but didn't think of it)

- 2.5 days after yeast pitch and sitting at 51F, had no activity on the Tilt
- Over the next 2 days, stepped up the temperature 1F every ~12 hours
- 4.5 days after pitch, still no gravity drop on Tilt after sitting at 58F

- Opened the fermentor, Tilt wasn't stuck, wort looked normal with no signs of fermentation.
- Pitched an old pack of Safale US05 (couple years past its best by date) in, started to see gravity drop 10 hours later while sitting at 56F

 

[IslandLizard]

Dang! Sorry to hear that.

- Wyeast 2206 Bavarian Lager smack pack was starting to swell before pitched (probably would've done a small starter, but didn't think of it)

The pack starting to swell is an indication (some of) the yeast was definitely alive, but likely a heavy underpitch.
I read somewhere that yeast won't start to ferment until the cell count has "saturated" the beer first.

What was the (best by) date on that pack? Shipped during hot weather?
How sure are you the beer temp was around 51F, and not far below?

I've learned to always prepare and pitch large starters, even from "fresh" packs, and especially with Lagers (doubling the pitch rate used for ales).

 

[Deadalus]

You pitched the yeast at 72F. I don't understand your thought of "they were frozen out"? I haven't used that specific yeast, but I routinely build starter lager yeasts at room temp. I don't think the yeast would have minded the range you were in. I wouldn't have pitched at that temperature for a batch though. I used to do it if I was over the temp some and let the yeast and the beer cool down and wouldn't say it was a big problem but I've read it's better to pitch lower temp than fermenting if not at the desired temp. So I have been chilling and then pitching. My sanitation is good.

I know you said there was swelling in the pack but I think you must have had a low viable cell count. Was the yeast shipped? When? Any kind of date on the cell pack? Most of my yeast gets shipped so I almost always make a starter, even if not shipped,as I overbuild and store a few bottles for future use.

What kind of chiller now, glycol right? 5.5 hours to drop 21 seems a little slow. What portion of the coil is submerged at 4.5 gallons? I have X2s but they are in use so I can't estimate. Did you go back and check multiple times or have a wifi readout? Not important in my view to the yeast situation, just wondering.

 

[Deadalus]

Sorry mostly just reiterated what @IslandLizard said. But yes, where's the thermowell? I built a small electric BK. I took off the original dial thermometer and soldered an NPT bulkhead there for the thermowell. I should have put it lower but between the element, whirlpool portand pickup tube I used that thermometer hole. But it's around the 3 gallon mark and I have to be careful about the volume. It's controlled by a PID, and if the volume drops it does the opposite and starts getting overly hot as the probe is measuring the air temp.

Is your Tilt calibrated? If you were using its record without confirmation with your temp controller, you might have been lower. Although that's a more unlikely situation.

 

[micraftbeer]

Answers:

- The thermowell was about 1.5" under the level of beer.
- Yes, the Tilt was calibrated (to match my calibrated Thermoworks Thermapen)
- Both the Tilt floating at the top of the beer, and the probe in the thermowell matched (within a degree of each other)
- I bought the yeast from my LHBS, had a best by date of 11/10/2025, vs an 8/10/2025 brew day
- I can't say for sure until I empty the beer from the fermentor, but I think the cooling coil is probably 4-6" below the beer level and 8" exposed above it.
- It's a glycol chiller

 

[micraftbeer]

So does anyone know the science as to why it's recommended to pitch at temps to match your desired fermentation temp (or just below)? It's obviously easier to put in everything before you put the lid on the fermentor, and less likely for accidental contamination if you have to take the lid off later.

To be honest, I didn't realize the temperature was as warm as it was when I dumped it in, or I would have waited/chilled it first because I had heard similar advice. I was hoping if I could understand the science/reason behind pitch temperature I could understand if there were some rules of thumb I might follow for future lager batches so I could throw everything in and close the lid once, without freezing/stalling the yeast. If that's even what I've done here and didn't just have a sluggish batch that should've been built up in a starter first...