Calculating pre-boil vol by weight?

[PSGD]

I do BIAB mash with no sparging. So all of my water is in the kettle as strike water. I pretty much have my volumes figured out but occasionally depending on how the weather affects the boil-off rate I miss my volume. I use a pulley to lift the grain bag, out of curiosity I usually weigh the grain bag after squeezing it like it owes me. I've been trying to get an educated guess as to my volume. Generally I'm shooting for 7.75 gallons pre-boil. My grain bag generally weighs only 4 or 5 lbs heavier post-mash than the dry grain did. That's about a half-gallon. Where does the rest of my strike water go? Most of my recipes use 8.75-9 gallons water. I am guessing as I extract the sugars out, the spent grain loses weight and actually holds closer to a whole gallon of water. Am I on the right track?


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[Black Island Brewer]

You are. The grain holds considerably more water, even with the squeezing. If you're getting 75% extract efficiency, the weight of a pound of grain is reduced by that same 75%, as those starches-now-sugars are removed from the grain and added to your water (more or less, because the efficiency is based on the weight of the grain having NO moisture to begin with, but in brewing it starts around 4% moisture). So the grain retains quite a bit of water, far more than 4%.

 

[Beernik]

There are five main water loss variables:
1. Evaporation during the mash and boil. I boil off about a gallon an hour, or about 15% per hour with a 5 gallon (post boil) batch.
2. Grain absorbtion. This is usually 0.1 to 0.2 gallons of water per pound of grain. It will depend on how fine you mill your grains and squeeze your bag.
3. System losses. This is water that you can't drain from your system (mash tun, BK). This amount is unique to your system.
4. Shrinkage. 1 gallon of boiling wort takes up more volume than 1 gallon of pitchable wort, about 4% difference.
5. Trub losses. This is water absorbed in hop particles/cones, hot break, and cold break. This can be as much as 0.5 to 0.75 gallons.

 

[wilserbrewer]

Always check preboil volume, with the bag hanging over the kettle, it is very easy to sparge, pour a little water over and through the bag to make a few extra pints of wort, making your pre boil volume spot on. A mark for preboil volume on your brew spoon mash paddle will help.
Cheers!

 

[PSGD]

I do need to make marks on a spoon for measuring volume. My kettle is a very simple 53qt pot with no holes in it. I don't want to clean anything extra like valves, dip tubes etc. That is until I build my bottom draining E-keggle


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