Converting batch sizes

[Monkeyguts]

Hey Men,
I have had a mind blank just when I am calculating my new brew. My pre-boil volume is 56 L and my post boil is 42L. When I convert batch sizes, say from a 23L recipe, do I use the 56L or the 42L?
Cheers in advance.

 

[Jack of all biers]

Assuming the 23L is the fermentor volume then 42L.

EDIT - by the way 14L is a lot to be losing during a boil. Is that right?

 

[warra48]

42

 

[Monkeyguts]

Assuming the 23L is the fermentor volume then 42L.

EDIT - by the way 14L is a lot to be losing during a boil. Is that right?

Yes, that is how much I lose. What sort of amount should I be losing? I just have it as a rolling boil, nothing over the top. I boil for 90 minutes.

 

[Jack of all biers]

On average a good rolling boil (system dependant of course) tends to boil off 10% per hour. That's somewhere in the vicinity of 15% for 90 mins or 8.4L for your pre-boil volume . Yours is at 25% evaporation over 90mins. There are no hard and fast rules here as boil off rate is very system dependant. I wouldn't worry, as long as you're system isn't burning the wort, you are not having to over sparge to achieve the pre-boil volume (thereby increase the chance of tannin extraction) and you are hitting your OG targets. If you're not getting any negative affects then you have dialled your system in to where you need it. If you are then try turning the heat down on the kettle to reduce evaporation losses.

 

[Danscraftbeer]

Batch size = Wort volume in the fermenter.
My pre boil is ~56l for a batch size of 40l.
There is 4lt trub left in the kettle so its really 56-44=12lt boil off evaporation.
Also consider the small details like cool shrinkage etc. -1lt
Beersmith is my friend.

 

[Jack of all biers]

I may have been confused there Monkeyguts. Did you mean you lose 14L in the boil and what is left over in trub? ie 10 litres in evap and 4L in trub. If so, ignore my posts and carry on.

 

[Monkeyguts]

I may have been confused there Monkeyguts. Did you mean you lose 14L in the boil and what is left over in trub? ie 10 litres in evap and 4L in trub. If so, ignore my posts and carry on.

No, I didn't take the trub into consideration. Thanks for the info. I will turn my heat down once I get that boil started.

 

[Jack of all biers]

Just turning the heat down by itself won't necessarily be great. If you're hitting your target OG and volume whilst losing 14L to evap then you've got your system set and I wouldn't advise playing with it. It would just cause frustration if you end up with 2-4L more, but the OG is way low.

Only if you are over sparging or getting issues from such evap (as mentioned above) should you rectify it by reducing evap, but you would also have to change your recipes. If you do go down the path of setting lower heat out put, then I suggest testing with water and measuring your losses. You may have to do it a couple of times to get the balance between good boil and lower evap.