topping up wort with water

[jgress]

I usually brew all-grain 1-gallon batches and I frequently have to top up the wort with extra water to get to the gallon mark, but only about an inch at most. However, I finished mashing grain for a dry stout and there was like less than a cup of liquid at mash out, and after sparging and boiling I ended up maybe a half to two thirds a gallon of what looked like pretty thick concentrated wort, so I had to add lots of tap water to make up for it. My suspicion is that the flaked barley in the mash just absorbed all the liquid, and I'm hoping that the amount of fermentable sugar after sparging still ended up the same (aiming for about 4.2% ABV if that helps), but in your experience could this be a concern?

Yes I know I should just take OG readings, but I admit I don't habitually take gravity readings for 1-gallon batches since wort is precious for small batches. So apart from that, is this the kind of thing I should strive to avoid in future, e.g. by adding extra water to the mash in case I think it'll all get sucked up by the grain?

 

[robfar]

Use 0.12 gal/lb of grain as your absorption. That will tell you how much "extra" water to add to the mash to account for grain absorption.

preboil volume + grain absorption volume = mash+sparge volume.

 

[McKnuckle]

Preboil + Grain Absorption + Mash Tun Dead Space = Mash + Sparge

(Applicable to some setups; not a problem with BIAB)

Also, why not take an OG reading and just pour back the sample? You're at the very beginning; no need to sacrifice at that point, and OG is kinda important or at least useful. Or invest in a refractometer so you can measure gravity with a couple of drops.