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Old 08-18-2012, 02:43 AM   #1
mcm114
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Default Extra low volume boils

So what's the least amount of boil volume anyone has used, and how did it work out?

When using extract, it seems like the only practical reason to boil at all is to extract hop bitterness, and of course sanitize the wort. But more and more people, including myself, are having good if not better results by adding significant portions of the extract at the end of the boil. So what if you only boiled the amount of wort necessary to fully isomerize the hop alpha acids, and added the bulk of the extract at the very end? (And topped up to 5 gallons, or whatever.)

I have done boils as low as 2-3 gallons before, but I want to experiment with boils in the range of 1 gallon and below. And, these would not be concentrated boils. The boil gravity will be approximately the same as the OG, i.e. 1# DME/gal water. Of course, the remaining extract would have to be raised to an appropriate temperature for sanitation purposes. (Maybe not if it was in a sealed package...)

Anybody tried this? Am I missing something important?

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Old 08-18-2012, 03:01 AM   #2
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Boil volume effects hop extraction efficiency. Are you using hopped extract or adding hops to your extract?

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Old 08-18-2012, 06:39 AM   #3
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Unhopped extract.

I know that specific gravity affects hop utilization, i.e. in a concentrated boil. But that's not what I'm talking about.

I don't see how the overall scale of the boil would affect hop utilization that much. But if it did, I think it would be easy to calculate and make adjustments for. I don't use brewing software, but maybe someone here could run the numbers and see the predicted hop utilization in a 1 gal. boil versus a 5 gal boil, with s.g. and everything else remaining the same.

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Old 08-18-2012, 06:55 AM   #4
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Update:

According to 2 different sites that calculate IBU's, the relationship between hop utilization and total volume is a linear one. That is the total IBUs in a 1 gallon batch are 5x higher than in a 5 gallon batch, everything else being equal.

BTW, the sites I found were www.brewersfriend.com and www.brew365.com

I know, it doesn't mean they're right...

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Old 08-18-2012, 01:22 PM   #5
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I've been doing the "steep small and boil big". The next tweak I want to try is late extract addition. I think the reason you wouldn't want to boil small is scorching the extract. That along with the hop utilization .

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Old 08-18-2012, 01:41 PM   #6
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The limiting factor in a small boil would be the IBUs from the hops. That would be fine in low IBU beers, but not in a beer with high IBUs.

What I mean is this- there is a limit to the amount of hops oils that can be isomerized in wort before becoming "saturated". Most experts say that is +/- 100 IBUs as a max.

So that means even if you had 10 ounces of high AAU hops in a 5 gallon boil, the maximum IBUs you'd get is 100 (some say lower, but we'll just call it 100 for now).

That's fine, as that's about the limit of human perception anyway. So, you could make a 5 gallon batch with 100 IBUs and it would be be a very bitter beer.

But if you're boiling 1 gallon, and topping up to 5 gallons afterwards, that means you'd have 1 gallon of 100 IBUs, and 4 gallons of 0 IBUs. So the maximum IBUs you'd be able to get in any beer is 25 IBUs total. That's not enough bittering for most beers, except for the lower IBU beers. Certainly not for an IPA or pale ale.

That's often why people who do partial boils complain of a too-sweet IPA. It's not the recipe, but diluting the 70 IBU wort by half means a 35 IBU wort.

It's not so much gravity that impacts utilization (and in fact has been proven recently that it doesn't at all), but it has to do with break material and the limits of the isomerization of the hops oils.

A larger boil will allow more isomerization of the hops.

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Old 08-19-2012, 12:13 AM   #7
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For an all-grain batch, the IBU are calculated (and reported) based on 6.5 gallons and not the final volume. Should I reporr the final IBUs based on 5 gallons instead?

Thanks, Nil

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Old 08-19-2012, 01:48 AM   #8
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Quote:
Originally Posted by Yooper View Post
The limiting factor in a small boil would be the IBUs from the hops. That would be fine in low IBU beers, but not in a beer with high IBUs.

What I mean is this- there is a limit to the amount of hops oils that can be isomerized in wort before becoming "saturated". Most experts say that is +/- 100 IBUs as a max.

So that means even if you had 10 ounces of high AAU hops in a 5 gallon boil, the maximum IBUs you'd get is 100 (some say lower, but we'll just call it 100 for now).

That's fine, as that's about the limit of human perception anyway. So, you could make a 5 gallon batch with 100 IBUs and it would be be a very bitter beer.

But if you're boiling 1 gallon, and topping up to 5 gallons afterwards, that means you'd have 1 gallon of 100 IBUs, and 4 gallons of 0 IBUs. So the maximum IBUs you'd be able to get in any beer is 25 IBUs total. That's not enough bittering for most beers, except for the lower IBU beers. Certainly not for an IPA or pale ale.

That's often why people who do partial boils complain of a too-sweet IPA. It's not the recipe, but diluting the 70 IBU wort by half means a 35 IBU wort.

It's not so much gravity that impacts utilization (and in fact has been proven recently that it doesn't at all), but it has to do with break material and the limits of the isomerization of the hops oils.

A larger boil will allow more isomerization of the hops.
I'm sure there is a limit to the IBUs you can get in wort, but I believe the 100 IBU number/limit is the maximum IBUs you can get in fermented beer. I think you can get much higher in unfermented wort. I saw some numbers (working from memory now) of 200 IBUs being measured in wort.

"and in fact has been proven recently that it doesn't at all". I thought this was still up for debate. All the IBU calculators still have a factor for boil volume, so they haven't made this change.
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Old 09-11-2012, 04:00 AM   #9
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buy a bigger pot really

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Old 10-02-2012, 09:01 AM   #10
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This is exactly the thread I need.

I have a 10 litre pot I use for boiling hops, topping up with about 12 litres after the boil. I imagine I am also watering down my hoppy wort but you should be able to double the hops the recipe calls for and hoppy get something better, right?

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