What do I calculate the boil-off from? Simple the pre-boil and after-boil sizes?

[Elysium]

Is it from the pre-boil and the after-boil size? Or is it supposed to be pre-boil and final amount of wort?

I am actually asking because I use brewtoad to make my recipes and there is only one option in the recipe maker that is related to the batch size. Basically, there am I supposed to put the after-boil size (amount that includes the trub, equipment loss and shrinkage) or simply the wort that goes into the fermentor?

I think one problem with brewtoad is that they dont account for loss of wort between the boiling and fermentor.

 

[guldalian]

Usually batch size refers to how much will go into your fermentor. So that is subtracting boil off, shrinkage, and trub/equipment loss. For instance, all my recipes are for 5.5 gal. I start with 7 gal at the beginning of the boil, but after all that stuff, I pour 5.5 gal in my bucket to pitch.

 

[Captain Damage]

There is no "standard" boil off rate. This will vary depending on your equipment configuration. To get the rate, just test it yourself. Put a couple of gallons in your kettle, boil it for an hour and measure how much is left.

 

[Elysium]

There is no "standard" boil off rate. This will vary depending on your equipment configuration. To get the rate, just test it yourself. Put a couple of gallons in your kettle, boil it for an hour and measure how much is left.

I am not talking about one, always-the-same boil-off rate. Every time you brew....depending on different things the boil-off will vary....in my case...depending on the strength off the heat, the room temperature...these are 2 things that vary all the time making the boil-off amount always slightly different.

But since I know certain things...such as pre-boil amount, after-boil amount....I can calculate it myself. My question is..is it preboil minus afterboil, or is it preboil minus what goes into the fermenter? This is a stupid question....but I am wondering which one is correct...because my recipe maker only has one option for "batch size".....and I am wondering if that should be looked at as final size or afterboil size.

 

[guldalian]

You are correct that technically speaking variables change the boil off rate from batch to batch. I've found this to be negligible though. So just try and find your "average" boil off rate for your equipment and use that when calculating your water needs. And yes, that amount is just pre boil vol - post boil vol. Post boil vol is not the same as batch size. Batch size= post boil-shrinkage-trub/equipment loss. Whatever that # is (for me it's usually 5.5 gal), use that for "batch size" in the brewing software.

 

[EROK]

I am not talking about one, always-the-same boil-off rate. Every time you brew....depending on different things the boil-off will vary....in my case...depending on the strength off the heat, the room temperature...these are 2 things that vary all the time making the boil-off amount always slightly different.

But since I know certain things...such as pre-boil amount, after-boil amount....I can calculate it myself. My question is..is it preboil minus afterboil, or is it preboil minus what goes into the fermenter? This is a stupid question....but I am wondering which one is correct...because my recipe maker only has one option for "batch size".....and I am wondering if that should be looked at as final size or afterboil size.

Boil off is (Pre-boil volume - Post boil volume) / pre-boil volume.

Example (7.5g pre - 6.5g post) / 7.5 pre = 13.33% Boil Off Rate

 

[rigatron]

I am not talking about one, always-the-same boil-off rate. Every time you brew....depending on different things the boil-off will vary....in my case...depending on the strength off the heat, the room temperature...these are 2 things that vary all the time making the boil-off amount always slightly different.

But since I know certain things...such as pre-boil amount, after-boil amount....I can calculate it myself. My question is..is it preboil minus afterboil, or is it preboil minus what goes into the fermenter? This is a stupid question....but I am wondering which one is correct...because my recipe maker only has one option for "batch size".....and I am wondering if that should be looked at as final size or afterboil size.

I think the variable that most complicates matters is not knowing how much water the mash will absorb. I imagine that's as significant as the actual boiling off of steam. This would probably vary with the types of malts/grains.

 

[Elysium]

Boil off is (Pre-boil volume - Post boil volume) / pre-boil volume.

Example (7.5g pre - 6.5g post) / 7.5 pre = 13.33% Boil Off Rate

ok,...cool. I think this can help me make in auto-calculator in excel.
Thanks.

 

[BryceL]

Boil off is (Pre-boil volume - Post boil volume) / pre-boil volume.

Example (7.5g pre - 6.5g post) / 7.5 pre = 13.33% Boil Off Rate

Not trying to get off topic here, but I believe boil off should be a gal/hour measurement, not percentage. For my setup I am always going to boil off 1.5 gal/hr whether I do a 5 or a 10 gallon batch, assuming I am using the same equipment for each. If I was to use the same percentage for each size batch, I would be off. For example...

(12.5g - 10g) / 12.5g = 20%

(6.5g - 5g) / 6.5g = 23%

I suppose using percentages is fine if your always doing the same batch size, just something to be aware of if you switch it up.

To the OP, to me batch size would be whatever volume you want to end up in your fermenter (your "final" size)..which is going to be even smaller than your post boil size.