AAU calculations

How do I work out AAU per gallon ? If I want one gallon of 12% AAU and the hops I have are 12% how much would I put in for one gallon and if I was to double the volume to two gallon would I double the amount of hops ? Can you put the answer in the Simplest terms possible as I am new to brewing. Thank you for any help.

In addition to this I am in the UK so grams would be fantastic if possible

Your question is a little confusing, AAU's are not expressed as a percentage. AAU's are alpha acid units, where you take the AA % of a hop and multiply by ounces. So one ounce of 12% AA hops would be 12 AAU's, 2 ounces would be 24 AAU's. Some recipes call for AAU's, although more typically you see it expressed as an actual weight.

Recipes are scalable, so to convert a 5 gallon recipe to 1 gallon just divide all ingredients by 5.

Is that what you were wanting to know?

Yes that's around about it I am reading a recipe that is for 5 gallons and it tells you to add 12% AAU which would be 1 ounce if the hops I have have a measurement of 12% alfa acid ? Am I right so far ? So what would I do if I wanted to only make one gallon would I still just decide this by five ? I think what I am wanting to know is when it comes to Alfa Acid measurements is there a rule of thumb when it comes to measuring them out so if I am making only one gallon and designing my own recipe an wanted 12% AAU would I use one ounce of hops with a rating of 12% or would it be less due to the low volume of water ? If that makes more sense

scorpien222 said:

Yes that's around about it I am reading a recipe that is for 5 gallons and it tells you to add 12% AAU which would be 1 ounce if the hops I have have a measurement of 12% alfa acid ? Am I right so far ? So what would I do if I wanted to only make one gallon would I still just decide this by five ? I think what I am wanting to know is when it comes to Alfa Acid measurements is there a rule of thumb when it comes to measuring them out so if I am making only one gallon and designing my own recipe an wanted 12% AAU would I use one ounce of hops with a rating of 12% or would it be less due to the low volume of water ? If that makes more sense

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You're getting the idea. Yes, divide the amount of hops by 5 if you're doing a 1 gallon batch. Think of this in terms of an IBU rating though and it may solidify your understanding.

AAU = AA% x (weight in oz of hops)

So 1 oz of 12%AA hops is 12AAUs.

Example: We're trying to hit about 22 IBUs. For a 5 gallon batch, the recipe calls for 12AAU of xbrand hops. What would this be for 1 gallon? Assume a utilization of .121 and use the IBU equation from Palmer's How to Brew.

Originally (12AAU x .121 x 75 )/ 5 gallons = 21.78 IBUs

For 1 gallon you'll find you need 2.4AAU of 12%AA xbrand hops or 0.2oz

(2.4AAU x.121 x 75)/1 gallon = 21.78 IBUs

AAU is not really what matters in a recipe. You want the IBUs or the HBUs which come from the AAU. 12 aau is always going to be 1 oz of 12% hops. If you want to maintain the same bitterness levels then you scale the measurements appropiately. 1 gallon would need 1/5th the hops as a five gallon batch. 10 gallons would need twice the hops of a five gallon batch. A brewing program really comes in handy for these calculations. Hope this helps you out.

edit: Too slow and sidepart did the math part too. Nice explanation!

sidepart said:

You're getting the idea. Yes, divide the amount of hops by 5 if you're doing a 1 gallon batch. Think of this in terms of an IBU rating though and it may solidify your understanding.

AAU = AA% x (weight in oz of hops)

So 1 oz of 12%AA hops is 12AAUs.

Example: We're trying to hit about 22 IBUs. For a 5 gallon batch, the recipe calls for 12AAU of xbrand hops. What would this be for 1 gallon? Assume a utilization of .121 and use the IBU equation from Palmer's How to Brew.

Originally (12AAU x .121 x 75 )/ 5 gallons = 21.78 IBUs

For 1 gallon you'll find you need 2.4AAU of 12%AA xbrand hops or 0.2oz

(2.4AAU x.121 x 75)/1 gallon = 21.78 IBUs

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So am I right in thinking that the 75 is a fixed number and does not change ? What about the .121 where do you get that number from ? Sorry if I am sounding a little dumb I have been reading John palmers book and There are just a few things that I personally dont think he explains massively well it could just be me though

The 75 is a fixed correction factor, the .121 is utilization which depends on boil time and gravity of the wort (see table in the book). Honestly though, this is why folks plug their recipe into brewing software or an online calculator (a number of free ones out there). I never do these calculations by hand.

chickypad said:

The 75 is a fixed correction factor, the .121 is utilization which depends on boil time and gravity of the wort (see table in the book). Honestly though, this is why folks plug their recipe into brewing software or an online calculator (a number of free ones out there). I never do these calculations by hand.

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Is there any software in particular you would recomend ?

For the average 1.050-ish beer in a 5-gallon batch, you can roughly estimate your utilization factors as 25% @ 60 minutes, 10% @ 15 minutes, and 0% @ 5 minutes or less. It's not perfect, but it will get you in the ballpark.

scorpien222 said:

Is there any software in particular you would recomend ?

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BeerSmith is cheap and easy... I still prefer to do things by hand though honestly... unless you get heavy into all-grain, then it's nice to have some tools.

You're quick and easy answer was to add 1/5th of the hops. If you're following a recipe, not a big deal. If you still really want to understand why, here's where you can re-read in Palmer.

http://www.howtobrew.com/section1/chapter5-4.html
http://www.howtobrew.com/section1/chapter5-5.html

I arbitrarily picked .121 in my example but I would normally get this from the table in Chapter 5.5.

IBU = AAU x Utilization x 75 / batch size (in gallons).

Using the table, just match up your OG and the amount of time you plan to boil the hops to get the utilization. (i.e. 60 minutes and your beer is 1.040 OG, that would give you a u = .252). Not to confuse the subject, but you'll want to use your pre-boil OG with this table. If your recipe is 1.040 gravity and it's a 5 gallon batch, you're probably starting with 6 gallons (some of it will boil off in an hour). Well your gravity is going to be less than 1.040 when you add the hops because you have more water in your pot initially.

Keep reading the Palmer's book. It's all there, and it's where I got my start. The influences of these equations start to make more sense as you start brewing.

sidepart said:

BeerSmith is cheap and easy... I still prefer to do things by hand though honestly... unless you get heavy into all-grain, then it's nice to have some tools.

You're quick and easy answer was to add 1/5th of the hops. If you're following a recipe, not a big deal. If you still really want to understand why, here's where you can re-read in Palmer.

http://www.howtobrew.com/section1/chapter5-4.html
http://www.howtobrew.com/section1/chapter5-5.html

I arbitrarily picked .121 in my example but I would normally get this from the table in Chapter 5.5.

IBU = AAU x Utilization x 75 / batch size (in gallons).

Using the table, just match up your OG and the amount of time you plan to boil the hops to get the utilization. (i.e. 60 minutes and your beer is 1.040 OG, that would give you a u = .252). Not to confuse the subject, but you'll want to use your pre-boil OG with this table. If your recipe is 1.040 gravity and it's a 5 gallon batch, you're probably starting with 6 gallons (some of it will boil off in an hour). Well your gravity is going to be less than 1.040 when you add the hops because you have more water in your pot initially.

Keep reading the Palmer's book. It's all there, and it's where I got my start. The influences of these equations start to make more sense as you start brewing.

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I think it will make more and more sense as I get going I have only done a bit of wine so far and I am just researching beer so I have at least a rough idea of what I am doing to start with I think I am going to start with palmers India pale ale recipe as my first.

scorpien222 said:

Is there any software in particular you would recomend ?

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I think many of us would recommend BeerSmith 2. You can download a free trial online, it's ~$20 to register it. It's worth every penny, IMO.

Ok it's all starting to make sense now one more question though when working out the IBU I assume I am using the total batch size and not just the boil amount ? Is that right because when I add the rest of my water this will surely dilute the bitterness of the wort ?

scorpien222 said:

Ok it's all starting to make sense now one more question though when working out the IBU I assume I am using the total batch size and not just the boil amount ? Is that right because when I add the rest of my water this will surely dilute the bitterness of the wort ?

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Calculate everything based on your final batch volume.

By the way, there are two formula's for calculating IBU's: Rager and Tinseth. They don't provide the same answers. Furthermore IBU's aren't always an accurate measurement of how bitter the beer is or seems. These values are estimates of the isomerized alpha acids. You would need a spectraphotometer to actually measure it. Furthermore, if you have an IPA with 70 IBU's and a stout with 70 IBU's, the percieved bitterness will be remarkably different.

The takeaway from this is that the IBU's are more of a reference point for designing you beers. They should have an expected bitterness quality that seems to suit the style you are brewing. You should use the same formula for calculating your IBUs in your beers so that you are consistent, but don't let it dominate your brewing.

ludomonster said:

Calculate everything based on your final batch volume.

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Shouldn't this post-boil volume?

That's what I meant.

So at what point would you take the OG ? And how do you work out the expected OG ?

scorpien222 said:

So at what point would you take the OG ? And how do you work out the expected OG ?

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You take the OG reading post boil. Adjust for temp. And I'd highly recommend software to do the expected OG calculations for you.

NordeastBrewer77 said:

You take the OG reading post boil. Adjust for temp. And I'd highly recommend software to do the expected OG calculations for you.

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Ok thank you that's what I thought but I realised you need some idea of the gravity to work out the utilisation is there any software you would recommend ??

NordeastBrewer77 said:

You take the OG reading post boil. Adjust for temp. And I'd highly recommend software to do the expected OG calculations for you.

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And I assume you would work out the expected gravity on the quantity that you are planning in the boil for working out the utilisation I.E if you are making a batch of 5 Gallon but only boiling three with the hops and the malt the utilisation is based on the three which will have a higher gravity and lower utilisation that if the whole five gallons were in there ? Then take the OG post boil to work out alcohol content at the end.

Am I making this more complicated that it is or am I along the right lines ?

You're complicating it. It's debatable that hops utilization takes a hit in a higher SG or smaller boil. And I assume by malt utilization you mean mash efficiency, or the % or starch that gets converted to sugar during the sacchrafication (sp?) rest, that depends on a lot of factors, grain crush, water/grist ratio, temp, type of malt used, etc. and wouldn't apply to an extract batch. This is where software becomes very handy, there's equations to figure out efficiency and utilization, but it's far easier to use software.

Yes, if you are brewing an extract recipe and bringing it up to 5 gal post-boil, then the gravity of the concentrated wort will be higher than your expected OG. This will need to be considered when finding your utilization, as it drops with increasing gravity.

If you're brewing with extract only, you don't need to take an OG reading. DME gives you 44 points per pound per gallon. LME has 37 points per pound per gallon. 1 gallon of beer brewed with 1 pound of DME will have an OG of 1.044. A 5 gallon batch with 5 lbs of DME will work out like this:

5 lb DME @ 44 ppg : 5 x 44 = 220 points
in 5 gallons : 220 / 5 = 44 points
Convert to specific gravity : (44 * 10^-3 + 1) lb/gal => 1.044 lb/gal

Following on what ludomonster said, if your kit says your OG will be 1.044, you know that you have 220 gravity units (GU, same as points) for a 5 gal batch. If you are doing a partial boil of 3 gal and want the gravity of the concentrated wort, take 220/3 = 73.33 GU, or 1.073.