This is totally confusing......Palmer talking about how he calculates IBU

[Elysium]

Here he says (and I quote)

"The recipe volume is 5 gallons. The gravity is figured by examining the amount and concentration of malt being used. As noted in the previous chapter, dry malt extract typically yields about 40 pts/lb./gal. Since this recipe calls for 6 lbs. of extract to be used in 5 gallons, the calculated OG = 6 x 40 / 5 = 48 or 1.048

But, since we are only boiling 3 of the 5 gallons due to of the size of the pot, we need to take into account the higher gravity of the boil. The boil gravity becomes 6 x 40 / 3 = 80 or 1.080"

Now.....this is confusing for people who are new to this. Since maybe we boil the whole amount of wort to start with.

Secondly...if he only boils 3 gallons.....shouldnt he account for the loss both coming from the boil-off and the loss in the equipment?

He wont end up with a 5 gallon (Vrecipe) factor, nor 5 gallons in the fermentor.

So....I am wondering how to calculate IBU using his calculation of IBU = AAU x U x 75 / Vrecipe?

The Vrecipe there is the preboil volume, afterboil or the volume of the wort that goes into the fermentor?

I assume it should be calculated with the preboil volume in my case. (I boil all the wort...not only part of it as he does in the example).

Any thoughts on this?

 

[pricelessbrewing]

The website is fairly out of date on several things, as it's one of the initial revisions.

 

[BargainFittings]

The calculation is accounting for the fact that hop utilization changes based on the gravity. Lower gravity (full boil) will use less hops compared to a higher OG partial volume boil using the same units of malt extract.

This calculation takes into account small volume extract boils that will later be topped up.

If you top up the partial volume boil to the same ending volume as the full boil, and used the same amount of hops, your full boil batch would have more apparent bitterness.

 

[GuldTuborg]

Here he says (and I quote)...Now.....this is confusing for people who are new to this. Since maybe we boil the whole amount of wort to start with.

Maybe you do, but then it's clear you just follow the standard, unadjusted formula. Palmer seems to be providing an example to help cope with partial boils.

Secondly...if he only boils 3 gallons.....shouldnt he account for the loss both coming from the boil-off and the loss in the equipment?

He wont end up with a 5 gallon (Vrecipe) factor, nor 5 gallons in the fermentor.

If the recipe calls for topping up to 5 gallons, then 5 gallons goes into the fermentor, exactly. That's the volume you want to capture with Vrecipe.

So....I am wondering how to calculate IBU using his calculation of IBU = AAU x U x 75 / Vrecipe?

The Vrecipe there is the preboil volume, afterboil or the volume of the wort that goes into the fermentor?

I assume it should be calculated with the preboil volume in my case. (I boil all the wort...not only part of it as he does in the example).

Any thoughts on this?

That volume is the total amount of wort before transferring to the bucket/carboy. Water loss due to boil does not affect anything in these calculations.

 

[Elysium]

That volume is the total amount of wort before transferring to the bucket/carboy. Water loss due to boil does not affect anything in these calculations.

Thanks a lot. This is what I needed.

 

[GuldTuborg]

Thanks a lot. This is what I needed.

You're welcome.

To be clear, water loss does affect things, but the calculation is designed to cover standard procedures. It's all pretty complicated, and I certainly don't understand all of it, but the calculations are pretty darned accurate in the end, for most all setups.

 

[Elysium]

You're welcome.

To be clear, water loss does affect things, but the calculation is designed to cover standard procedures. It's all pretty complicated, and I certainly don't understand all of it, but the calculations are pretty darned accurate in the end, for most all setups.

I have been working on a spreadsheet that is basically a recipe maker, efficiency and IBU calculator.

I have reached a point where I open it (a simple excel file) and design a beer recipe from zero....almost without looking for extra information (I initially had to look up ppgs and hop utilization values and some other things). That's why I need to know these things.

 

[GuldTuborg]

Sounds like a handy device. I'm sure if you have the know how, it beats paying someone else to do it for you. I hope it continues to work well for you.