Restarting Fermentation After Cold Crashing

[Williac]

Thought I would post this up to assist with anyone who may need it in the future. We're brewing on a nano (1 barrel) setup but the principles should be the same.

We run three brew days in a row to fill 3, one barrel fermenters in our fermentation chamber. Given the lack of individual control we generally cold crash these at the same time once all have completed fermentation. Now, for the past few months we have been using the refractometer readings to indicate whether fermentation has completed (few days at the same) before taking a final reading with the hydrometer. Our process failed this time and after cold crashing it was obvious with one of our beers that something was up. A slight sweetness remained and it had a faint sour tang.

This didn't change or advance while the other two cold crashed so I held the hope that it hadn't been contaminated. It's not something that people should ever have to do on a regular basis but I decided to try and restart the fermentation. I raised the temperature of the chamber back up to casting temps over a three day period. I then added 3 teaspoons of Marmite to distilled water and heated it up using the same method as our gelatin additions (microwave bursts and stirring with a thermometer up to around 65-70C). This was added to the one barrel batch and a (very) well sanitized mash paddle was used to gently stir the beer and disturb the surface of the yeast cake back into the mixture.

This story would be way too lengthy of the process didn't work. Thankfully, after several hours the airlock was showing some activity and by the following morning the slight sour twang had disappeared and the beer had dried out to expected levels.

As I mentioned before, the best recommendation is to have the processes in place to avoid having to do this in the first place and we've adjusted ours accordingly. Point is, if you find yourself in this situation the beer may still be salvageable and this procedure can work. A few takeways:

- Fermentation can be successfully restarted after a cold crash has been conducted.
- Use yeast nutrient in conjunction with stirring up the top portion of the yeast cake.
- Yeast love Marmite (it's basically yeast cells after all).

 

[TheMadKing]

Simply warming it up should do the trick too. If that didn't work then the entire principal of liquid yeast would be in jeopardy. (Not intended to be snarky haha)

 

[petrolSpice]

Cold temps (above freezing) doesn't kill or even stop yeast. It only slows them down. In fact, it will keep fermenting even at cold temps, albeit very slowly. If you warm it back up the yeast will continue doing their job as before. You don't need to add sugar for this, but stirring the cake certainly helps as the cold causes some of the yeast to sink.

 

[Williac]

Fully agree, I probably should have mentioned that. I think the yeast nutrient is a handy addition at this point as it may not be the ideal conditions for getting the yeast to wake up again and complete their job at the best of health. I wasn't seeing any signs of reactivation after a few days back at fermentation temps but the cake stir and nutrient addition definitely got things rolling again!

 

[Williac]

Should be noted we always use dry yeast, only thing we have access to over here

 

[day_trippr]

And "over here" would be where?

If your yeast options are so limited, you should consider exploiting bottle dregs...

Cheers!

 

[Williac]

We'll be looking into harvesting our yeast at some point but have just started selling (only kegging for now) so consider a fresh pitch a safer option for the moment. One step at a time and all that.

We're based in Laos