Is it Possible to Collect Too Much Volume From Mash Tun?

Question

I'm still new to the all-grain scene and I've messed up my sparge more than once, leaving me with a pre-boil gravity that is too low. I got to thinking, if I fall short (in pre-boil gravity) in the future, I could simply do another sparge. Assuming I have room in my kettle, I don't see any harm in collecting a 3rd or 4th running --even if it gets my kettle volume higher than I want it to be. Naturally, I'll have to boil down the kettle until I reach my desired volume, but at least I'll have the sugar I failed to collect from the previous sparge (the water will boil away, but the sugar will stay behind).

As long as I don't throw extra ingredients into the kettle until the appropriate time, is there any harm with collecting additional runoffs and boiling the water long enough to reach my desired kettle volume?

Answer 1

Yes there is a risk - with each successive sparge you increase the risk of extracting tannins, causing the beer to taste "puckering"/astringent (think sucking on a teabag.) Before doing extra sparges, should also be sure that the low extraction is because of your lautering efficiency and not because of mash efficiency, so do an iodine test for complete conversion first.

If you do sparge extra, you'll need a longer boil, which uses more energy and may darken the wort a touch, so keep that in mind if you're aiming for a very pale beer.

Personally, I'm not sure it's worth it. I would just add some LME/DME if you're wildly under target, or just forget about it for small undershoot, and look at either anticipating this efficiency next time, or look at ways to improve lautering efficiency if you find that is the cause.

Unless you forgot to stir the mash or made some other mistake that affects lautering efficiency, subsequent run-offs are usually too small in volume and do not have a high enough yield to make any significant difference. Just add more fermentables directly to the kettle and chalk it up to experience!

Answer 2

Braukaiser's Batch Sparge Analysis does a good job of answering the multiple sparges question (summary). Regarding the negative effects of boiling longer, take a look at: Any reason not to boil for longer?

Basically, you run into diminishing returns after 2 batch sparges. If you're worried about efficiency, you also need to keep in mind the time cost of additional sparges plus boiling the wort for longer, in addition to the monetary cost of boiling the wort longer. Depending on how you value your time, it'll probably be cheaper overall to just add more grain to compensate for your effeciency, or look into other ways to improve it.