[flbrewer]

This has happened before and it happened again tonight. Apparently, my mash tun can create water out of thin air.

My mash water volume was 4 gallons, got 2.75 first runnings (close enough to expected).

My sparge water volume was 3.37 gallons, and I got 3.5 gallons back! Is it possible that after batch sparging and stirring around the grain, it somehow "unlocks" some extra water that didn't come out during the first runnings?

Or is it simply magic?

[Frankenbrew]

No magic. I think that all the grain-water absorption takes place during the mash. So after you run off the mash water, the grains are saturated and don't take on any more water. Your second runnings should be more or less the same volume as the sparge water you add.

[flbrewer]

Yeah, I know they should be the same, but how am I getting more? Now that I think about it, 3.5 gallons and ~3.4 aren't too different.

[HoosierBrew]

No magic. I think that all the grain-water absorption takes place during the mash. So after you run off the mash water, the grains are saturated and don't take on any more water. Your second runnings should be more or less the same volume as the sparge water you add.

+1.  Sounds like the first runnings could've been drained a little more thoroughly too, explaining why the sparge amount came out a little higher than what was put in.

[flbrewer]

No magic. I think that all the grain-water absorption takes place during the mash. So after you run off the mash water, the grains are saturated and don't take on any more water. Your second runnings should be more or less the same volume as the sparge water you add.

+1.  Sounds like the first runnings could've been drained a little more thoroughly too, explaining why the sparge amount came out a little higher than what was put in.

How would you do this? I use a Rubbermaid 10 gallon cooler and at some point, the wort stops flowing. Even if I tip it, there is no more liquid coming out.

[morticaixavier]

it keeps coming out, just very very slowly. put the end of your runoff hose in a container while you go on with your brew and see how much more drains out over the course of an hour.

[Frankenbrew]

it keeps coming out, just very very slowly. put the end of your runoff hose in a container while you go on with your brew and see how much more drains out over the course of an hour.

Yes, I find that I will get a quart or more over the course of the boil up.

[Iliff Ave]

Sometimes my volumes are low. I have to close the valve, shake the cooler, and let it sit for a couple of minutes before collecting the last bit of wort. Stirring the grain around also helps to free any wort however that kind of defeats the purpose of establishing the grain bed.

[HoosierBrew]

In the past I've used a small rectangular cookie sheet that fits into my cooler, to gently press down on the grain bed and get an extra quart or so of wort, to hit my target volume. My volumes are dialed in pretty tightly now, though.

[euge]

I just let my cooler drain the last drops into a gallon pitcher. You'd be surprised how much trickles out over the course of an hour. Then it gets added to the boil though some brewers like to make starters out of the runoff.

Always seems to me that I get more out of my second sparge too. The mash is mushier and I think it just lets loose of more liquid after being hypersaturated.

[ynotbrusum]

There must be a physics based answer, but danged if I know what it is.  My experience has been the same (maybe the thinness of the second runoff allows a greater suction of liquid by a very small degree in terms of the siphon....)  Or its magic.

[Jimmy K]

I suspect the answer is because you are adding plain water and removing water with dissolved sugar (dissolved out of the grain). If you dissolve table sugar in plain water the total volume will increase slightly.

[HoosierBrew]

I suspect the answer is because you are adding plain water and removing water with dissolved sugar (dissolved out of the grain). If you dissolve table sugar in plain water the total volume will increase slightly.

Sounds pretty spot on to me.  Hadn't thought of that.

[denny]

This has happened before and it happened again tonight. Apparently, my mash tun can create water out of thin air.

My mash water volume was 4 gallons, got 2.75 first runnings (close enough to expected).

My sparge water volume was 3.37 gallons, and I got 3.5 gallons back! Is it possible that after batch sparging and stirring around the grain, it somehow "unlocks" some extra water that didn't come out during the first runnings?

Or is it simply magic?

Yeah, it must be something like that.  I regularly get about 1/2 gal. less from my mash and the same amount more from my sparge than I anticipate.  Since I end up with the correct volume, I don't worry about it.

[brewerbrandon]

I imagine the fluidity of the grain bed increases draining off the higher gravity work and passing mashout temperature water through the bed. The sparge water has a lower specific gravity than the work and is less viscous as well. The diffusion of wort sugars away from the grain must also increase as the osmotic pressure increases. Have you tried continuous sparging?