All Grain, Partial Boil???

I do BIAB all-grain, full boil occasionally supplemented with DME for higher gravity beers. Because of set-up limitations this requires me to do two separate boils.

I used to do partial boils and top-off. When I was doing this I was dissatisfied with the end product. But I have changed so many things since then which now has me doubting that topping off was truly the cause of my dissatisfaction. And I'd like to be able to shorten my brew day.

I know that partial boils can darken the wort. And I know that some believe there is lowered hop utilization (whether it be as a result of increased wort concentration or increased hot break concentration).

So, now my question...

Does anyone think there is something else that is suboptimal with topping off? My concern is that there is further change that occurs during boiling that benefits the overall taste and that this is lost with top off water. Whether its a chemical change related to acid-base reactions or whatever.

I just can't get off the idea that top off water dilutes taste of the beer compared with the same OG full boil technique.

I'll probably stick with what I'm doing now until I buy new equipment and/or move to a place with outside space. But, in the meantime, any thoughts? Opinions?

People effectively do this all the time when they overshoot their efficiency on the mash. They end up with a higher pre-boil gravity than desired, so if they don't want to end up with a bigger beer than they expected, they top off in the boil kettle to reach their expected gravity. The book Designing Great Beers has a chapter called "Hitting Target Gravity" that is very informative about this with calculations on how to figure this out.

But this technique is more for accounting for efficiency differences, and the topping off is done pre-boil. I'm not sure what the effect would be to do this intentionally and top off after the boil.

I'm guessing the difference is more mental than real, though I imagine the caveats given about partial boils with extract regarding wort darkening and hop utilization still apply. This is just a guess...never tried what you're stating, so maybe somebody more authoritative can chime in.

I've done it a couple times and never noticed anything wrong with it. It'll likely produce a slightly different product for the reasons you noted, but I wouldn;t say there is anything off with doing it.

Yes. I have a refractometer and I have used it to nail down a pre-boil gravity. I have had to add more or less water to my second sparge and once I added water pre-boil to get to my goal pre-boil gravity.

But in those cases I felt a little better because:

1. The amount I added was fairly small.

2. All the water is still in the boil and will undergo all chemical reactions that occur during the boil.

Adding water at the end feels like a different ballgame.

dcp27 said:

I've done it a couple times and never noticed anything wrong with it. It'll likely produce a slightly different product for the reasons you noted, but I wouldn;t say there is anything off with doing it.

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It may not be off. But even if it's suboptimal I would stick with a split full boil. If I could get good beer with a partial boil but could have better beer with a full boil, I'd pick the latter even with a longer brew day.

ayoungrad said:

Yes. I have a refractometer and I have used it to nail down a pre-boil gravity. I have had to add more or less water to my second sparge and once I added water pre-boil to get to my goal pre-boil gravity.

But in those cases I felt a little better because:

1. The amount I added was fairly small.

2. All the water is still in the boil and will undergo all chemical reactions that occur during the boil.

Adding water at the end feels like a different ballgame.

Click to expand...

Does the water itself actually undergo any chemical reactions, other than killing nasties, and evaporation? I mean, aren't the chemical reactions you're concerned about in brewing more regarding the soluble extract from the mash, and the hop oils?

I get what you're driving at, but don't know how adding water post boil would literally water the beer down more than boiling with the full volume, and arriving at the same post boil volume through evaporation.

The chemistry of wort boiling is actually fairly complex and there are chapters dedicated to it in larger brew texts. And water and it's dissolved salts play a role in the at least some of the reactions. So I guess what I'm getting at is, has the water from the boil been effectively changed in a way that would differentiate it from adding water to the boil later. Honestly, it could be as simple the fact that fewer salts react with phosphates in the boil, so there are effectively more salts in the top off water. Or the final pH is thrown off from the added water. I have a chemistry background but it is still a difficult thing for me to figure out.

My gut tells me that there is a difference. Just like concentrated anything, once diluted with water tends to taste different. Not necessarily better or worse I suppose, but definitely different.

I see where you're going, and thought about dissolved salts/minerals, and how a the boil might affect these, cause them to precipitate, undergo chemical change, etc. I figured (gut feeling, not drawn from any expertise) that this will not have as big an effect on flavor during the boil as the difference in wort gravity. I do not have a chemistry background, so won't pretend to know the answer.