high gravity after boil

[hellbent]

Hi Guys,
I have just brewed up a DSGA 12ltr and all went well right up to the boil. My SG prior to boil was 1.035 @ 45c which calibrated to 1.044 (brewmate suggested 1.042) so I'm happy there, but my reading after boil was 1.056 @ 42c, this calibrated to 1.064 (compared to brewmates 1.047) now this seems like a bloody big difference somehow!! I done my hops @ 45, 10, 5, and the aroma ones will go into the fermenter, I lost about 26% in evap during the 60 min boil. Any one got any ideas of why it could be happening, how to improve it or how to prevent it from happening again??
Cheers guys
Al

 

[tallie]

What are the pre and post-boil volumes in Brewmate? Those actual numbers look about right to me, assuming when you said you lost 26% you mean you had a post-boil volume of 8L:

44 x 12 / 8 = 66 (as in, 1.066)

If you want to end up at 1.047, you need a post-boil volume of 11.23L (ie, 44 x 12 / 47). You could add back water to dilute it; you'd need 3.23L (ie, 11.23 - 8 )

Cheers,
tallie

edit: fix SG number

 

[Mardoo]

Agreed, pre and post-boil volumes are needed to be sure but it sounds like evaporation. That's pretty high for a total evaporation and can lead to some different flavors arising than if the evaporation were lower. My last brew had a similarly high total evaporation and it came out great. You can always dilute before your pitch but be sure you use boiled water.

 

[Nick JD]

Small batches lose much more to evaporation than large ones.

It's all about surface area to volume ratios. Reduce your boil vigor.

 

[hellbent]

What are the pre and post-boil volumes in Brewmate? Those actual numbers look about right to me, assuming when you said you lost 26% you mean you had a post-boil volume of 8L:

44 x 12 / 8 = 66 (as in, 1.066)

If you want to end up at 1.047, you need a post-boil volume of 11.23L (ie, 44 x 12 / 47). You could add back water to dilute it; you'd need 3.23L (ie, 11.23 - 8 )

Cheers,
tallie

edit: fix SG number

thanks tallie, I wasn't sure if I could dilute but will now....Brewmates pre boil was 1.042..........post boil was1.047....

Nick it wasn't an overly strenuous boil but I will tone it down a bit more and see what vhappens
cheers

 

[tallie]

thanks tallie, I wasn't sure if I could dilute but will now....Brewmates pre boil was 1.042..........post boil was1.047
cheers

What were the expected volumes in Brewmate though?

You can dilute, but as Mardoo alluded to, make sure you use clean water. If it has already started fermenting, you also want to use water with low dissolved oxygen. Using water that's already been boiled and cooled in a clean environment will help with both of those.

Or you could just leave it be and chalk it up to experience.

 

[hellbent]

What were the expected volumes in Brewmate though?

You can dilute, but as Mardoo alluded to, make sure you use clean water. If it has already started fermenting, you also want to use water with low dissolved oxygen. Using water that's already been boiled and cooled in a clean environment will help with both of those.

Or you could just leave it be and chalk it up to experience.

Wort volume expected in Brewmate before boil was16.8 which was close to spot on.......... After boil volume expected in BM was 14.00.... Final Vol 12.5... evap allowance was 16.5.

I use tank water but will boil up 3ltrs and then do I just add that to fermenter with wort, shake it up a bit to aerate, then add my saf 05? or add the Saf first then shake?? some say don't shake it and some say do and after just reading a post about different forms of aeration I'm totally confused.

 

[tallie]

Wort volume expected in Brewmate before boil was16.8 which was close to spot on.......... After boil volume expected in BM was 14.00.... Final Vol 12.5... evap allowance was 16.5.

I use tank water but will boil up 3ltrs and then do I just add that to fermenter with wort, shake it up a bit to aerate, then add my saf 05? or add the Saf first then shake?? some say don't shake it and some say do and after just reading a post about different forms of aeration I'm totally confused.

Ok, ignore all the calculations in my first post! I thought 12L was the pre-boil volume. The expected numbers don't add up to me and I don't have time right now to write out the calc's, but if your expected post-boil volume was 14L and your actual was 12.5L, you should only add back 1.5L.

I take it from your second paragraph that you haven't pitched the yeast yet? Unless you've no-chilled the wort in a cube, there is an increased chance of infection if you've left it this long. I aerate before pitching, but it shouldn't matter much if you do it straight afterwards; as long as the yeast is mixed in thoroughly and it doesn't get left on the sides of the fermenter after shaking.

To be honest, if it was me at this stage, I'd be pitching as soon as possible and not worrying about diluting. Just aim for a less vigorous boil next time and if it's still too much, add the water back before the end of the boil.

 

[felten]

On small batches I float one of those aluminum roasting tins on top of the wort to reduce boil off. Reduced my boil off from ~25% down to ~15% an hour.

Maybe something you could try next time.

 

[bum]

On small batches I float one of those aluminum roasting tins on top of the wort to reduce boil off. Reduced my boil off from ~25% down to ~15% an hour.

Really? Using an aluminium pie tin on my wort seems to increase boil vigor. I would assume this increased vigor would also increase boil off? Never run the same brew with and without the plate to compare the difference.

 

[hellbent]

Ok, ignore all the calculations in my first post! I thought 12L was the pre-boil volume. The expected numbers don't add up to me and I don't have time right now to write out the calc's, but if your expected post-boil volume was 14L and your actual was 12.5L, you should only add back 1.5L.

I take it from your second paragraph that you haven't pitched the yeast yet? Unless you've no-chilled the wort in a cube, there is an increased chance of infection if you've left it this long. I aerate before pitching, but it shouldn't matter much if you do it straight afterwards; as long as the yeast is mixed in thoroughly and it doesn't get left on the sides of the fermenter after shaking.

To be honest, if it was me at this stage, I'd be pitching as soon as possible and not worrying about diluting. Just aim for a less vigorous boil next time and if it's still too much, add the water back before the end of the boil.

Ok mate thanks for your more than kind assistance..... I heavily glad wrapped the top of the kettle 10mins after boil as in a no chill as per usuall with intentions of adding it to fermenter when cooled to approx 24c then add yeast. ......the 14ltr post boil vol allows for 1.5kg trubs etc and .5 after cooling loss making it 12ltr finished brew.
Cheers Tallie and thank you.
Al

 

[hellbent]

On small batches I float one of those aluminum roasting tins on top of the wort to reduce boil off. Reduced my boil off from ~25% down to ~15% an hour.

Maybe something you could try next time.

maybe worth a try...I'm a bit worried about to slow of a boil but will try and see what happens.
thanks
Al

 

[Spiesy]

Small batches lose much more to evaporation than large ones.

It's all about surface area to volume ratios. Reduce your boil vigor.

Damn striz-aight.

I have no idea why people continue to quote % boil off rates... % of volume isn't as important as actual volume lost.

If you're using a small, 12l, batch - you're % of volume evap rate is going to be vastly different than in a 24l batch, in the same vessel at the same boil intensity... probably twice the %.

 

[felten]

On small batches I float one of those aluminum roasting tins on top of the wort to reduce boil off. Reduced my boil off from ~25% down to ~15% an hour.

Maybe something you could try next time.

Sorry that 25% was a typo, supposed to read 20%.