Sparge volume for batch sparging a partial mash

First off: I realize there are a few somewhat related questions but I think my question will be specific enough to justify it's own question. Specifically this question, but I'm not looking for an alternative solution(s) such as the accepted answer.

I am going to try my first partial mash this weekend, and since I have the equipment on hand, I want to use my converted cooler mashtun. Partially to get used to the equipment before going full mash.

I will be using about 5 lbs of malt (4 two-row, 1 specialty). So I was planning on using the 1 quart per pound- so 1.25 gallons of striking water. I'd like to try the batch sparge technique and I'm planning on a 7 gallon boil.

I know with small mashes there are many techniques and it really doesn't take too much to get the sugars out. But I want to emulate a "proper" batch sparge yet compensate for the lower volume.

My question is should I split the 5.75 gallons (7 - 1.25) into 2 even sparges of ~2.875 gall , or should I do 2 sparges of a smaller volume and just add additional water to get to the boil volume?

edit: I was looking at my 5 gal recipe and not the 6. There will be 5 lbs of two-row and 1.75 specialty in the mash and 5 lbs dme. I'm not changing numbers in the question so that the answers still have relevant calculations.

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How much extract are you adding and what's the target SG? The recipe you have so far gives you a 6 gallon post boil of around 1.021-ish. – brewchez Feb 4 '12 at 0:54
it's actually 5 lbs of 2 row, 1.75 pounds specialty, and 5 lbs DME. It's calc'd at 1.060 OG on Hopville – j_syk Feb 4 '12 at 2:35

You say you want to get to as close as a full mash\sparge as possible, but scaled down so that you are prepared for a full mash. In practice, this means using an amount of water proportinal to contribution to the OG contributed by the mash. For example, if you were to get half of your OG from extract, and half from the mash, then you'd aim for 3.5 gallons of runoff from the mash\sparge, and simply top up with 3.5 gallons as contribution from your extract.

The other point of view is that you can use the full 7 gallons of runoff and add the extract to that. Although this doesn't emulate a full mash, since you are using much more water than you would use for a full mash, you will get the best extraction efficiency from the grain.

I would go for using the full 7 gallons of runoff from the mash\sparge - there is so much difference between the partial and the full mash that you might as well take the benefit of being able to use more water. If you were fly sparging, then getting to know and recognise a good run-off rate is beneficial, but since you are batch sparging, I would simply use the full volume. In fact, this is a pretty close approximation of the full mash, since you'll be using only a slightly smaller volume of sparge water when doing a full mash anyhow. If you're full grain bill ends up being 10 pounds, then that's just a little under half a gallon per sparge, assuming you sparge twice.

Sparging twice gives better efficiency than sparging once when batch sparging, so definitely do that regardless of your runoff volume. See the link below for details.

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I thought I had come across some resource that said it's possible to over sparge. if so, does that just refer to having more sparge+runoff than boil volume? Or is it detrimental to sparge too much even under the boil size? (and I mean in theory, not practice. we all know you can do all sort of "bad" things and still get good beer) – j_syk Feb 3 '12 at 22:15
see my edit - I added a link to batch sparging analysis. In practice, it's very hard to oversparge a batch sparge. But even if your final runoff is low SG, you can reduce chances of tannin extraction by adjusting the pH to be below 6. But that's really just theory, I think you will be fine just sparging the grain you have. I do 10 gallon batches - 14 gallons runoff - with little more than 10 lbs of grain, and have never had any astringency problems from batch sparging. – mdma Feb 3 '12 at 22:26
thanks mdma. Now I need to decided what do do about equipment. If I do full volume runoffs, I'd have to use my boil pot for a hot liquor tank. I guess I need to use something else to hold either the first runnings or the hot water in the interim. Oh no, a cheap excuse to buy another brew pot or cooler. Probably the latter though – j_syk Feb 3 '12 at 22:34
I think its certainly easy to oversparge 5 lbs of malt with 7 gallons of water, regardless of what the batch sparging "rules" are. – brewchez Feb 4 '12 at 0:37
Increase your mash ratio to 1.75 qt./lb. It will improve your efficiency a bit and you won't have to sparge as much. – Denny Conn Feb 4 '12 at 16:49

With such a small mash compared to the final volume I'd shoot for enough sparging to just get your sugars out. In this case I'd shoot at a 4 gallon total. So at the end of the mash I'd add in 0.75 gallons of boiling water to raise the mash to mash out. (Not necessary, but it does help a little but with lowering viscosity IMO). Recirc a little to clear the wort and set the bed. Run off and collect that in the kettle. Then I'd add another 2 gallons of wort, stir, recirc and run off.

I'd add my missing three gallons of water for the 7 total. Measure the gravity and add in the extract you need to hit your target pre boil gravity.

Something you haven't accounted for yet which is EXTREMELY important in such a small mash is grain absorption and dead volume. The grain will absorb some water that you just can't collect. Usually 10% of the total volume is a good target, expect it to be 0.125 quarts or a cup of water. Second you should really fill your mash tun with a measured volume of water and drain it without grain it in. The measure the water you get out of the tun and see what's missing. This volume also should be accounted for in the make up water for that first sparge. SO where I said add 0.75 it will be a little more. Something like 0.75gal plus the cup for absorption, plus a little to over come the dead space. Your dead space might be a big issue with a small mash. In fly sparging dead space becomes a small factor in the efficiency, but in batch sparging I have found it to be a big contributor if your tun's geometry doesn't allow for a really great drain.

Do it this way prepares you for handling your larger sparges in the future. Factoring in things like absorption and tun dead space. For most beers in the 1.045-1.060 range the volume issues I mention become less of an issue. But if you decide to brew a session beer and start pushing the lower end of your tuns performance (like your partial mash) managing the smaller volumes of a smaller mash becomes important.

I batch sparge some low gravity english style ales routinely. When I do I often find myself sparging and collecting less than my target boil volume just because the grist bill doesn't require more. So I add a couple gallons of water in the kettle to get to my target preboil OG.

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