Fermentation restart during Diacetyl Rest

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I've had an American Amber Ale fermenting with US-05. It was scheduled to ferment at 19C for 10 days and then have a diacetyl rest at 21C for three days, before a soft crash to dry hop.

It had pretty much finished after 7 days and there was really no activity from the airlock until the raise to 21C and I'm now getting periodic bubbles again - maybe one every three minutes or so. I feared some kind of wild-yeast infection, but the FG is stable at 1.013 (predicted to be 1.014) and, other than there being a lot of yeast in suspension, it tastes great.

I don't think I've ever noticed this before, but does the yeast generate CO2 when it's processing diacetyl as well as when it's processing sugar?
 
A two degree temperature rise will result in some volumetric expansion of the contents of the fermenter. SO if you're raising the temperature quite slowly then expect a few bubbles.
Also the CO2 is less soluble in the beer as the temperature rises so, as above.
It's unlikely a yeast will stop and restart within that temperature range but an infection from outside could get it going again.
And, what @dmtaylor says. Get those hops in there now as they may well metabolise some of the higher sugars and they have bacteriostatic properties, which helps against ouside infections.
 
Thanks, both, for your comments. Volumetric expansion and the CO2 coming out of solution makes perfect sense. In terms of the dry hop, the reason I was planning to wait for soft crash before fry hopping is to avoid the possibility of the yeast generating diacetyl while processing hop compounds (I had this happen previously). Maybe I'll just chuck them in now, then!
 
Another reason to dry hop while still fermenting well around 3/4 days. Those that dry hop late on after main ferment run the risk of hops restarting fermentation you pays your money and takes your risk
 
Another reason to dry hop while still fermenting well around 3/4 days. Those that dry hop late on after main ferment run the risk of hops restarting fermentation you pays your money and takes your risk
Yeah, I sometimes think I attempt to approach brewing too scientifically for my own good (and capability). I think it's because I don't fully understand what biotransformation will give to my beer, so I try and leave it out of the equation for now.

As it is, I just spent 20 minutes searching the fridge, freezer and ingredient boxes and couldn't actually find the Cascade for the DH, neither do I have any of the suggested substitutes, so I just lobbed in some leftover Mosaic and El Dorado. The hell with it - this is turning in to the least scientific brew ever, but it might be the best thing I've ever brewed :D
 
IMO you are right you can get too scientific with this hobby, if thats what floats your boat then do it but too many brewers become frightened of not doing the latest process exactly as described by a expert but in this world there are always experts who are advocates of different techniques so who is right?
Just find what works for you and do it is my motto and take into consideration this hobby is becoming a expensive one if you bought every latest gadget(do not forget the manufacturers need to be finding the next thing to make money from and giving them to youtube brewers etc for a "FREE" trial always gives a rose tinted view-they are like politicians in their reviews Oh and another saying nothing is free in this world) athumb..
 
I'm all about the science I'm afraid...well not so much the science but the process. I am a manufacturing engineer by trade so the endless effort to eradicate or control every single variable is the obsession I'm afflicted with.

I've got into the habit of raising temps a degree a day for a few days or so once fermentation appears to halt. Sometimes I'll eke out a further gravity drop or two, but often not. Whenever it completely finishes I usually leave it a good week after the last sign of any gravity drop before considering fermentation done.

I'll soft crash to 13 - 15 degrees to dry hop (not decided which is the best temp yet). Firstly it starts the process of yeast flocculation...I dump as much yeast as possible before dry hopping as I don't want those hop oils in the trub - also if you drop a litre or so trub it reduces the amount of hops needed to achieve a specific g/litre dry hop rate, then dry hop after that in an attempt to prevent further fermentation activity from the dry hop. I've never experienced hop creep, but always keep an eye out for it - thats the benefit of a floating hydrometer.

As for biotransformation...I've never achieved it...done several back to back brews to see if I can achieve it but haven't...other than the dry hopped during active fermentation versions are always not quite as bright and aromatic and those dry hopped after fermentation and therefore inferior to my tastes and what I'm trying to achieve. I dont think the difference is anything to do with biotransformation. I think its a combination of longer hop contact time which is inevitable if you dry hop during active fermentation, drawing out those less bright and more grassy flavours from the hops, and loss of intensity due to hop oils being absorbed into the trub - you're pouring lovely smelling trub down the drain when you dry hop on trub. Yet to try the thiolised approach with thiolised yeasts and utilising mash hopping, but have tried a few commercial beers of this type which do seem to have a unique 'twang' to them. Not sure if it's a good or bad twang yet.
 
I dry hop and use a bag with SS spoons(to weigh the hops down) so that the hops can be removed after 2 or 3 days of contact. I am not frightened of oxidation by opening and removing the hops and only do a short hop time wise as long ones are not needed as most of the flavour is extracted within this time period.
Just proves brewing and brewers are different in their approach. So find what works for you
 
I'll soft crash to 13 - 15 degrees to dry hop (not decided which is the best temp yet).

The hop book I read recently recommended dry hopping at 4c, reckoned it worked quicker at lower temperatures and transfer was 80% complete in 6 hours.

Not sure if it's a good or bad twang yet.

I did an experimental brew recently (based on ideas in the hop book) and the result certainly is different. I really like it, the missus doesn't even like the smell (but the daughter does). Do you want to try it ? I'm doing some posting tomorrow.
 
The hop book I read recently recommended dry hopping at 4c, reckoned it worked quicker at lower temperatures and transfer was 80% complete in 6 hours.



I did an experimental brew recently (based on ideas in the hop book) and the result certainly is different. I really like it, the missus doesn't even like the smell (but the daughter does). Do you want to try it ? I'm doing some posting tomorrow.

Sorry, that was vague who I was talking to - @hoppyscotty -do you want me to send you some of my thiol brew ?
 
Sorry, that was vague who I was talking to - @hoppyscotty -do you want me to send you some of my thiol brew ?
I'd love to give it a go...thanks!

And dry hop at 4C? never thought it'd be worth doing that cool. defo worth a go as I want to limit dry hop contact time to 24-36hrs (closer to 24hrs) and soft crashing and dry hopping for my desired contact time...then cold crashing for a few days extending the contact time is something that irks me - especially if cold dry hopping is effective. If I can dry hop while cold crashing then that solves that issue - set to cool, dry hop during cooling, then dump hops after say 36 hours once most of the hop matter has dropped out of suspension, then ready to condition/carbonate/package or whatever.
 
As it is, I just spent 20 minutes searching the fridge, freezer and ingredient boxes and couldn't actually find the Cascade for the DH, neither do I have any of the suggested substitutes, so I just lobbed in some leftover Mosaic and El Dorado. The hell with it - this is turning in to the least scientific brew ever, but it might be the best thing I've ever brewed :D

Well I just packaged it and it’s pretty damn good. As I couldn’t find the 15g of Cascade, I figured it wasn’t going to be the beer I had intended anyway, so I decided to increase the dry hop load to about 50g and the leftovers which went in happened to be 23g of Mosaic and 28g of El Dorado. It’s really, really tasty and it hasn’t even conditioned or carbonated yet.

19 litres in to keg and 5x 500ml PET bottles with two carbonation drops in each. I really can’t wait to tap this one in a couple of weeks. If I can wait that long…
 

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