Slow Ferments....what's the cause?

[adm]

When I started brewing back in July, I was amazed at how quickly the primary ferments went with S04 & US05 - 72 hours and it would be down at the 3/4 way mark...


However, my last few beers have been much slower to ferment and I am wondering it if is to do with the temperature.

I did a batch last Monday, OG was 1054, and today it's still at 1020. I would expect it to have got down to the target of 1013 by now.

Nothing has changed in my process - the FVs all sit in an unused room, which is not heated. Ambient temp in the there is 16.6C today - which is a couple of degrees cooler than the rest of the (also currently unheated) house which is at 19.0C. It was most likely a few degrees warmer in there in July and August though.

Is that likely to be the problem? They all start off fermenting just perfectly, but seem to take much longer to finish now.

The other couple of things that may be important is that the FVs are sitting on a marble plinth that extends from the fireplace in that room at floor level. This is probably a few degrees cooler that the ambient temperature.

Also - the brews that ferment slower have all happened since I started using yeast nutrient....although I would imagine this should actually make fermentation faster!

So what do you think - is it likely to be seasoal temperature changes causing this? And if so, is it worth insulating the bottom of the FVs from the marble they are sitting on, or moving them to a warmer location? I will have a temp controlled fermentation cupboard in the next few weeks, but for now I don't.

[Aleman]

I'd say it was temperature . . . My Imperial stout went from 1.092 to 1.025 in under 48 hours . . . but that's pitching a big amount of yeast (44g in 23L), and fermenting at 20-21C, as temperatures drop you need to up the pitching rate, even for ales. Pitching a lager (80L at 1.048) at 9C for example needs 200g of dry yeast . . . same beer at 15C needs 40g (And then rapid cooling once fermentation starts;) ).

[Stonechat]

I'd say it was temperature . . . My Imperial stout went from 1.092 to 1.025 in under 48 hours . . . but that's pitching a big amount of yeast (44g in 23L), and fermenting at 20-21C, as temperatures drop you need to up the pitching rate, even for ales. Pitching a lager (80L at 1.048) at 9C for example needs 200g of dry yeast . . . same beer at 15C needs 40g (And then rapid cooling once fermentation starts;) ).

Totally agree with Aleman's reply, but a small word of warning to those thinking of going down the "big yeast hit" road: make sure you leave enough headroom for a very vigorous fermentation.
I used 23g of S-04 in 27litres of a 1069OG beer last Wednesday and it blew the lid off the 33litre fermenter twice.
I suspect Aleman had the sense and experience to ferment what looks like a short brewlength for him, in one of his larger fermenters.

For the record the yeast head dropped into the beer leaving it pretty clear, with a very thick layer of yeast on the FV bottom by Saturday AM, when it was down to 1016.

Hope this helps prevent others having to clear up the worktop spillage

[Aleman]

a small word of warning to those thinking of going down the "big yeast hit" road: make sure you leave enough headroom for a very vigorous fermentation.

You mean like this

[Stonechat]

suspect Aleman had the sense and experience to ferment what looks like a short brewlength for him, in one of his larger fermenters.


Does this photo mean that the larger FV was not used, or does it mean that the yeast head was about 18" tall ?

[spearmint-wino]

I concur with Aleman too - it sounds like on this occasion it is down to temperature. There have been sporadic reports of S-04 only fermenting down to 1.020 then sticking, although I've not experienced it myself. Always pitch a good amount of yeast, aerate well and keep somewhere not to warm and not too cool and you shouldn't have any problems

[hoppingMad]

However, my last few beers have been much slower to ferment and I am wondering it if is to do with the temperature.\.

Yes thats the reason. You will get a much slower ferm at 14-16 than at 18 C. Also you will get less fruity esters which is a matter of style and personal taste. Personally I quite like using lager yeasts for some of my ales, and ferment them as low as 12-15 C for a "cleaner" taste.

I did a batch last Monday, OG was 1054, and today it's still at 1020. I would expect it to have got down to the target of 1013 by now.

Normal at your quoted temp.

The other couple of things that may be important is that the FVs are sitting on a marble plinth that extends from the fireplace in that room at floor level. This is probably a few degrees cooler that the ambient temperature.

Sounds exactly right. So you effective ferm temp could be even cooler. However, remember that fermentation is usually 2 degrees C warmer than ambient because of yeast activity.

Also - the brews that ferment slower have all happened since I started using yeast nutrient....although I would imagine this should actually make fermentation faster!

Your lower temp is the reason, not the addition of nutrient. The nutrient may or may not contribute to a faster fermentation and its hard to quantify this any way because there are just too many other variables. But the yeast nutrient will generally give a very slightly lower finish.

So what do you think - is it likely to be seasoal temperature changes causing this? And if so, is it worth insulating the bottom of the FVs from the marble they are sitting on, or moving them to a warmer location? I will have a temp controlled fermentation cupboard in the next few weeks, but for now I don't.

You would get a one or two degre C increase just by insulating the FV with an old duvet both underneath and at the top and sides. If you want more incease then you would need some form of heat. I have used an electric blanket in the past with a thermometer sticking out the top. But now use my lagering fridge, the FV goes in there along with a tiny free standing oil heater which has its own thermostat. Gives excellent temp control for fermentation.
Cheers, Hopping.

[Aleman]

suspect Aleman had the sense and experience to ferment what looks like a short brewlength for him, in one of his larger fermenters.


Does this photo mean that the larger FV was not used, or does it mean that the yeast head was about 18" tall ?

That's a 25L fermenter with 23L of wort in it . . . its sat inside my 100L fermenter . . . . Thank goodness . . . . Must get myself a larger 25L fermenter

[adm]

Thanks chaps,

I'm just back from a week away and the two brews in FV haven't really moved. The Old Nick is at 1018 and Gail Porter is around 1022. Mind you, both are tasting excellent - so maybe there's something good to be said for long slow ferments.

I'm trying to decide what to do now as I need at least one of the FVs back to brew tomorrow.

I might just rack them both to secondary and add a little bit of rehydrated S04 to them. What do you think? Then leave them for a few weeks and see where they have got to after that - I'm not in any rush as I'm away for two weeks from Monday and have 4 cornys full of beer in the fridge.