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Beerlust

Pre-Boil Gravity

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I have a question for full volume brewers whether they be extract or AG'ers.

At full volume, to end up with 19-23 litres post boil, what is your pre-boil gravity for a beer aimed at being 5.0% ABV in the keg? (no secondary fermentation)

I'm looking to improve my small boil/partial mash beers around this level. I feel the 1.040 SG mark I've been using generically via IanH's spreadsheet may actually be flawed on this level. I feel it may be a little low given the IBU I hit & the general ABV I make my beers to, & that an adjustment here would help.

It's something I have been thinking about for sometime now about changing, so will be interested in views on this.

Cheers & good brewing,

Lusty.

Edited by Beerlust

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It depends on what the boil off rate is, it also depends on the mash temp and other variables that influence the FG. Mine would usually be around 1.042 pre boil to get an ABV at about 5% in the keg with a "standard" mash temp around 66 degrees. 

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Thanks Kelsey for your setup variables.

I'm less concerned with boil off rates, but accept they definitely play their part in this, so thanks for mentioning it.

The thing is with my small volume boils, the boil-off rate is similar to full volume (may even be the same?), but the big difference is in how rapidly mine escalates to very high gravities/low utilisation levels due to the lower starting volume. Once I have my smaller volume post boil wort it would be at a very high gravity compared to a full volume brewer. I then dilute this to some degree into my fermenter. My utilisation levels throughout the boil are obviously affected differently (some might even suggest adversely) to that of a full volume brewer.

Cheers,

Lusty.

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Yeah you can't really compare it between full volume boils and smaller ones because like you say the SG would increase a lot more in the smaller volume. I usually get an increase of about 8-9 points over a typical 75 minute boil, but I'm starting with 35 litres and boiling off about 3.5ish. 

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For reference, my standard pale ale using 5kg grain for a 23 litre volume has the following stats:

Pre-boil - 1046
Post-boil - 1051

That is after a 60 minute boil.

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12 hours ago, Beerlust said:

The thing is with my small volume boils, the boil-off rate is similar to full volume (may even be the same?)

I have read that the diameter of the pot can make a difference. The larger diameter means there is greater surface area and the boil off will be greater.

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10 hours ago, Hairy said:

I have read that the diameter of the pot can make a difference. The larger diameter means there is greater surface area and the boil off will be greater.

Spot on Hairy. 🙂

Cheers,

Lusty.

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I wanted to do a sanity check for some IBU values I've been getting from the IanH spreadsheet. I'm doing some extract-only boils, usually a 3L boil for a 10L batch. If I put 25g of Saaz (4.0%AA) for a 30 minute 3L boil, I get an IBU of 16.2 in a 10L batch, right around where I want to be. However, using the Brewer's Friend IBU Calculator (and several others), I get around 7 IBUs.

Is this because these other IBU calculators are made for homebrewers who are doing full volume boils? So when I enter 3L for my boil size and 10L for my batch size, this assumes I have added all my extract into the 3L, rather than a small portion into the boil and the larger part into the fermentor after the boil. This would give a boil gravity of around 1.153, giving a much poorer utilization than the 1.040 boil gravity I aim for.

FYI, I am using the Hop Concentration Factor in the spreadsheet and my target OG is 1.046.

TIA, Cassius.

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You should have 10l boil volume even though your only boiling 3l. See if that changes things.

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20 minutes ago, Titan said:

You should have 10l boil volume even though your only boiling 3l. See if that changes things.

If I put 10L boil and batch size on the Brewer's Friend calculator, while leaving the rest of the parameters the same, I get 20.2 IBUs. I'm not really sure where that leaves me, haha.

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Try 11l boil and 10l batch as you will lose some volume in the boil.

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You have to ensure your boil volume is 3l in brewerfriend just like it is in the spreadsheet.

The difference in the numbers is due to the app thinking you are doing a full volume boil of 10l versus a small boil of 3l. The full volume boil would have a larger IBU figure, 20.2 versus the smaller boil of 16.2.

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On 12/9/2019 at 6:09 PM, Beerlust said:

At full volume, to end up with 19-23 litres post boil, what is your pre-boil gravity for a beer aimed at being 5.0% ABV in the keg? (no secondary fermentation)

Great question. I cant tell you as I only measure my post boil gravity. However, my soft ware will give an indication and it states 1047. Which sounds a bit high to me. 

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18 minutes ago, Norris! said:

You have to ensure your boil volume is 3l in brewerfriend just like it is in the spreadsheet.

The difference in the numbers is due to the app thinking you are doing a full volume boil of 10l versus a small boil of 3l. The full volume boil would have a larger IBU figure, 20.2 versus the smaller boil of 16.2.

Yep, I had boil volume at 3L originally, and it gave 7 IBUs. Titan suggested trying 10L boil and batch, which gave the 20.2. I'm wondering at the discrepancy between the spreadsheet and Brewer's Friend for 3L boil and 10L batch. Spreadsheet gives 16.2 and Brewer's Friend gives 7.7.

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5 hours ago, Cassius said:

Is this because these other IBU calculators are made for homebrewers who are doing full volume boils? So when I enter 3L for my boil size and 10L for my batch size, this assumes I have added all my extract into the 3L, rather than a small portion into the boil and the larger part into the fermentor after the boil. This would give a boil gravity of around 1.153, giving a much poorer utilization than the 1.040 boil gravity I aim for.

FYI, I am using the Hop Concentration Factor in the spreadsheet and my target OG is 1.046.

TIA, Cassius.

That is what I can see. Sorry for not reading your post fully. If you set the brewerfriend calculator to a boil gravity of 1.046 it is close to the spreadsheet.

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2 hours ago, MartyG1525230263 said:

Great question. I cant tell you as I only measure my post boil gravity. However, my soft ware will give an indication and it states 1047. Which sounds a bit high to me. 

It depends on what FG you end up with. If you can hit at least 1.012 before bottling you should end up with at least 5.0% ABV once carbed up in the bottle. 

Cheers,

Lusty.

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2 hours ago, Beerlust said:

It depends on what FG you end up with. If you can hit at least 1.012 before bottling you should end up with at least 5.0% ABV once carbed up in the bottle. 

Cheers,

Lusty.

Yep I get that it was more to do with the dilution factors of evaporation, contraction when cooling and a heat correction.  I had the SG for the brew at pitching at 1051 with 75% attenuation for a FG of around 1012.  As I say I only check the SG post cooling and the figure sounded a bit high to me but again i never use it.  I am surprised the corrections only get it to rise 4 points.  I thought they may have been more.  

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