Time to reactivate chilled yeast

[valdid_shaw]

I won’t bore you with the details but a blunder with my fermentation chamber meant after a couple of days fermenting my IPA at 18 degrees, it had a couple more with the temp dropped to about 7-8 degrees. I’m guessing fermenting will have kicked in again once the heat picked back up - but should I expect any other issues or take any precautions as a result?

 

[An Ankoù]

Shouldn't cause any problem at all, v-s. The couple of days at 18 degrees have given the yeast time to colonise the wort and become sufficiently strong to overpower most other infections (unless you're very unlucky). And it's an IPA so there’ll be plenty of late hops, which are, themselves, bactericidal. As soon as the wort warms up, it should take off again.
What yeast strain were you using, by the way?

 

[foxbat]

It depends on the yeast, some strains are rather keen to flocculate when the temperature drops below their preferred range. If that's happened then they might need some rousing.

 

[Slid]

I re-use dry yeast by storing the trub in small bottles in the fridge for up to 4 months without issues, so your yeast will have the wherewithal to prosper, but as Foxbat says, it may need a bit of rousing.

 

[valdid_shaw]

Thanks all. It’s just dry Safale US05 - nothing special. Will that need ‘rousing’, and what is meant by that? Do i just add a couple of days onto the fermenting time compared to what I’d normally do to make up for the sleepy 48 hours when it dropped cold?

 

[Dutto]

'Rousing the yeast" is usually applied when stirring up a "stuck" wort.

The idea is that stirring up the wort will reintroduce some oxygen and the living yeast in the trub will start working again.

Personally, I add a teaspoonful of Yeast Nutrient at the same time.

 

[valdid_shaw]

Thanks again. Having read up that Safale US-05 isn’t great at floculation I’m hoping enough of the yeast will have been suspended during the cold period that it’ll hopefully have restarted without the need for rousing. I’m due to dry hop in a day or so... would it be worth me taking a sample then and checking gravity to see if all is in order before taking any riskier steps like stirring it?

 

[An Ankoù]

Thanks again. Having read up that Safale US-05 isn’t great at floculation I’m hoping enough of the yeast will have been suspended during the cold period that it’ll hopefully have restarted without the need for rousing. I’m due to dry hop in a day or so... would it be worth me taking a sample then and checking gravity to see if all is in order before taking any riskier steps like stirring it?

Yep. Check that you final gravity is what you would have expected it to be or leave it an extra 3 days or so to make up for when it wasn't fermenting. US-05 is most forgiving. Rousing simple means stirring the yeast back into the beer so that it all goes murky again- with a sterilised paddle, stick, cat or whatever's to hand.