Different Fermentation Rates.

[Pommy Matt]

Hi all,
Fairly new to AG, brewed my 7th batch last Thursday, which was also my first double batch. Roughly the Northern Brewer SNPA clone, brewed a bit lighter and with a bit of added wheat.
I ended up with 48L of 1046 wort after hitting all my numbers pretty well. After rapid chilling to 20C, 27L of this went into a 30L fermentor, and the remaining 21L into another. Both fermentors put into a single large fridge set for 15C. Yeast was the slurry (US05) from a pale ale that I racked to secondary on the same morning as the brew, and each fermentor got the same amount - a schooner (not too scientific, I know).
So the interesting thing about all this is that today I checked the SGs of both, and the larger batch is sitting at 1028 (pretty slow), and the smaller batch is at 1012. Wort temp of both has been a more or less constant 18C.
The only differences I can possibly see are:

1. the amount of yeast pitched (relative to batch size) - this would have been higher for the small batch by about 25%.
2. Possibly the levels of aeration could have been different, since the aeration took place in the fermentor.
3. outsider - the smaller batch got filled second, and had a lot more trub than the 27L batch.

I'm not particularly worried about this, just thought it was an interesting observation. If anyone can think of any other reason for the difference (infection?) then that would be interesting. Otherwise, it is kind of eye opening to me that such seemingly small changes could make such a big difference to fermentation speed.

matt

 

[Amber Fluid]

I don't have any answers, just being new to AG myself. However, something to ponder over is the 6L difference in wort volume is nearly 33% more that the same amount of yeast pitch need to chew through.

 

[Pommy Matt]

I don't have any answers, just being new to AG myself. However, something to ponder over is the 6L difference in wort volume is nearly 33% more that the same amount of yeast pitch need to chew through.

yep - that's what I think it must be. I guess I have a ready made experiment on my hands also as to how the two differ in taste. The only thing is, I already planned to dry hop one but not the other, which might somewhat mask the differences due to pitch rate if there are any!

 

[bconnery]

Hi all,
Fairly new to AG, brewed my 7th batch last Thursday, which was also my first double batch. Roughly the Northern Brewer SNPA clone, brewed a bit lighter and with a bit of added wheat.
I ended up with 48L of 1046 wort after hitting all my numbers pretty well. After rapid chilling to 20C, 27L of this went into a 30L fermentor, and the remaining 21L into another. Both fermentors put into a single large fridge set for 15C. Yeast was the slurry (US05) from a pale ale that I racked to secondary on the same morning as the brew, and each fermentor got the same amount - a schooner (not too scientific, I know).
So the interesting thing about all this is that today I checked the SGs of both, and the larger batch is sitting at 1028 (pretty slow), and the smaller batch is at 1012. Wort temp of both has been a more or less constant 18C.
The only differences I can possibly see are:

1. the amount of yeast pitched (relative to batch size) - this would have been higher for the small batch by about 25%.
2. Possibly the levels of aeration could have been different, since the aeration took place in the fermentor.
3. outsider - the smaller batch got filled second, and had a lot more trub than the 27L batch.

I'm not particularly worried about this, just thought it was an interesting observation. If anyone can think of any other reason for the difference (infection?) then that would be interesting. Otherwise, it is kind of eye opening to me that such seemingly small changes could make such a big difference to fermentation speed.

matt

There are a number of factors.
The yeast count against the batch size is one definite factor, point 1 above.
Point 2, very doubtful to me that the amount of aeration would be sufficient to cause a big difference.
3. Not actually outside at all. Just because you put the same amount of slurry in each, or even more trub in one, the viable yeast count for each pitch could easily be variable resulting in differing behaviours between each...

 

[Pommy Matt]

There are a number of factors.
The yeast count against the batch size is one definite factor, point 1 above.
Point 2, very doubtful to me that the amount of aeration would be sufficient to cause a big difference.
3. Not actually outside at all. Just because you put the same amount of slurry in each, or even more trub in one, the viable yeast count for each pitch could easily be variable resulting in differing behaviours between each...

Just to be clear - the extra trub I am talking about is the trub from the kettle of the new brew - ie the hop residue and cold break in the bottom of the kettle. A fair bit of this made its way into the smaller fermentor (I was siphoning). I think the yeast slurry from the prior batch that I pitched with should have been similar for both, as I had given it a decent swirl about - but of course that could be a factor too.

cheers,
matt

 

[wessmith]

Just to be clear - the extra trub I am talking about is the trub from the kettle of the new brew - ie the hop residue and cold break in the bottom of the kettle. A fair bit of this made its way into the smaller fermentor (I was siphoning). I think the yeast slurry from the prior batch that I pitched with should have been similar for both, as I had given it a decent swirl about - but of course that could be a factor too.

cheers,
matt

Hi Matt,

You have a classic yeast health issue - not uncommon in general HB brewing. The extra trub would have provided the smaller batch with some extra yeast food. I would suggest you start using a yeast nutrient additive - have a look at the retail sponsors above for some options. (http://www.craftbrewer.com.au/shop/details.asp?PID=4279) As a general piece of advice, I ALWAYS use yeast nutrient to some degree - especially when using rain water or RO water.

Cheers,

Wes

 

[Pommy Matt]

Hi Matt,

You have a classic yeast health issue - not uncommon in general HB brewing. The extra trub would have provided the smaller batch with some extra yeast food. I would suggest you start using a yeast nutrient additive - have a look at the retail sponsors above for some options. (http://www.craftbrewer.com.au/shop/details.asp?PID=4279) As a general piece of advice, I ALWAYS use yeast nutrient to some degree - especially when using rain water or RO water.

Cheers,

Wes

Thanks Wes that's a very interesting take on it. I had been getting very fast fermentations after using similar amounts of yeast cake to this last brew. Usually I make little effort to keep the trub out of the fermentor, but this time I actually let the whirlpool settle in the kettle for a full hour before siphoning off, and ended up with one fermentor (larger batch) almost entirely free of trub, as that was the first to get siphoned off. From what you saying it might be better to leave more trub in the wort, assuming the rapid fermentation is desired. I will look into yeast nutrients for my next batch, thanks for the tip.

matt

 

[wessmith]

Thanks Wes that's a very interesting take on it. I had been getting very fast fermentations after using similar amounts of yeast cake to this last brew. Usually I make little effort to keep the trub out of the fermentor, but this time I actually let the whirlpool settle in the kettle for a full hour before siphoning off, and ended up with one fermentor (larger batch) almost entirely free of trub, as that was the first to get siphoned off. From what you saying it might be better to leave more trub in the wort, assuming the rapid fermentation is desired. I will look into yeast nutrients for my next batch, thanks for the tip.

matt

A "very fast fermentation" needs to be defined. Often a seemingly fast ferment will stall around 1020 and then v-e-r-y slowly creep down. Same problem - yeast health. As a guidline, a good ferment with an ale yeast like 1056 or US05 should ferment out in 3 to 4 days @ 18C. Lager yeasts are a little different usually requiring 7 to 10 days at 12C. I am assuming an OG of 1048 to an FG of 1008 to 1010 in the above statements. When you re-use the yeast cake you need to oxygenate AND provide extra nutrient as the previous ferment will have depleted the available nutrients.

Happy brewing,

Wes