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calculation of preboil volume


Apr 9, 2019
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Why BS3 mash/sparge water calculations are not inline with preboil volume calculation?
Preboil calculation only take into account batch volume, cooling shrinkage and boil off.
Same time if I adjust deadspace losses only amount of water changes but preboil stays same...
BeerSmith calculates the water volumes back from the batch size you set and the process losses in the equipment profile.  If you look at the vols tab in your recipe, the flow of volume calculation actually starts at the bottom and is calculated upwards to get your total water needs for mashing.  So when you change your deadspace loss, this does not change the amount of water needed pre-boil to attain your volume into the fermenter. 
I understand. But can you explain me please what in actualy meant under Mash Deadspace Losses?
For example I have Grainfather and if i pump all wort out there will be left over in tun in amount of 1,7l. I supposed this is Mash Deadpsace Loss.
In that case if I want to have 20l in fermenter I need to have 21,7l after boil. But changing this number does not affect on postboil volume (same time lost to trub and chiller does affect)
Couple of things.

First, mash tun dead space is the unrecoverable wort which cannot be drained from your mash tun.  This differs from the recoverable mash tun dead space in that this is the volume of wort which is not in direct contact with the grains but will be drained from the mash tun.

Second, your grainfather is an all-in-one unit so it really does not have a mash tun.  Your losses at the end should be considered under "trub loss" since this volume not only is not lost pre-boil, but also participates in the boiling process and therefore ends up with a higher concentration of sugar than it would have at the end of the mash.