Scaling American IPA to Double IPA regarding Bitterness: Focus on Absolute IBUs vs BU:GU ratio?

[Noob_Brewer]

Context: I brewed an american IPA which had an OG of 1.064 and calculated IBUs of 77.9 (including whirlpool additions). The beer turned out great and did very well in comps. Now Im wanting to scale this up to a double IPA with an OG of 1.075, and Im seeing some things that Im getting confused about. Ideally, I want the same percieved bitterness as my American IPA was. I use Beersmith. What beersmith is showing me is if I simply up the OG from 1.064 to 1.075 and don't keep the IBU level (ie the absolute volume of hop additions remains the same ) the BU:GU ratio obviously drops from 1.210 to 0.958 BUT the calulcated IBUs also drops to 71.8. So as OG increases and hop additions are unchanged, the calculated IBUs also goes down. was always under the impression that if you put a 60minute addition of a hop in for 20IBUs, this should still be 20IBUs regardless of gravity but the BU:GU ratio will obviously go down with increasing gravity. So beersmith seemingly adjusts the absolute IBU level when gravity changes but hop additions stay the same. If I target the same BU:GU ratio of 1.210 from my american IPA (OG 1.064) and adjust my double IPA (OG 1.075) to achieve the same ratio, my IBUs for the double IPA will be 91.3.

Concern/Question: I'm not sure if I should focus on upping the absolute IBUs vs the BU:GU ratio to accomplish this. These two variables seem to not be linear with each other. Will targetting the same BU:GU ratio really leave the perceived bitterness when drinking the beer the same? This is my goal: up the OG and keep the same perceived bitterness. Seems there are multiple moving parts here and me not knowing WHY Beersmith (or likely other calculators) lowers the absolute IBU level when gravity increases is a bit of a mystery to me. So BOTH the BU and GU change at the same time and not one staying the same while the other changes.

Now I will shamelessly tag others who have given me great advice on HBT but others are also and always welcome to chime in... @Dgallo @wepeeler @secretlevel @ihavenonickname

 

[Dgallo]

Context: I brewed an american IPA which had an OG of 1.064 and calculated IBUs of 77.9 (including whirlpool additions). The beer turned out great and did very well in comps. Now Im wanting to scale this up to a double IPA with an OG of 1.075, and Im seeing some things that Im getting confused about. Ideally, I want the same percieved bitterness as my American IPA was. I use Beersmith. What beersmith is showing me is if I simply up the OG from 1.064 to 1.075 and don't keep the IBU level (ie the absolute volume of hop additions remains the same ) the BU:GU ratio obviously drops from 1.210 to 0.958 BUT the calulcated IBUs also drops to 71.8. So as OG increases and hop additions are unchanged, the calculated IBUs also goes down. was always under the impression that if you put a 60minute addition of a hop in for 20IBUs, this should still be 20IBUs regardless of gravity but the BU:GU ratio will obviously go down with increasing gravity. So beersmith seemingly adjusts the absolute IBU level when gravity changes but hop additions stay the same. If I target the same BU:GU ratio of 1.210 from my american IPA (OG 1.064) and adjust my double IPA (OG 1.075) to achieve the same ratio, my IBUs for the double IPA will be 91.3.

Concern/Question: I'm not sure if I should focus on upping the absolute IBUs vs the BU:GU ratio to accomplish this. These two variables seem to not be linear with each other. Will targetting the same BU:GU ratio really leave the perceived bitterness when drinking the beer the same? This is my goal: up the OG and keep the same perceived bitterness. Seems there are multiple moving parts here and me not knowing WHY Beersmith (or likely other calculators) lowers the absolute IBU level when gravity increases is a bit of a mystery to me.

Now I will shamelessly tag others who have given me great advice on HBT but others are also and always welcome to chime in... @Dgallo @wepeeler @secretlevel @ihavenonickname

I do not know the exact math but it’s a ratio of wort composition and alpha acids.

As the og goes up with the same amount of hops, the ibus get lower because the ratio widens and vice versa.

If you want to dive into it, here’s an article. The Oxford Companion to Beer Definition of International Bitterness Units (IBUs).

 

[Noob_Brewer]

I do not know the exact math but it’s a ratio of wort composition and alpha acids.

As the og goes up with the same amount of hops, the ibus get lower because the ratio widens and vice versa.

If you want to dive into it, here’s an article. The Oxford Companion to Beer Definition of International Bitterness Units (IBUs).

Thanks man, I'll dive into this. Because the absolute IBUs goes down with increasing OG (despite hop additions remaining unchanged), its a conundrum on how to adjust this to get the same "perceived" bitterness of the lower gravity beer becuase both variables in the BU:GU ratio change. With that same logic, if you keep the same BU:GU ratio as you increase the OG, this might increase the "perceived" bitterness unnecessarily. Of course "calculated" vs "perceived" bitterness likely aren't the same. So Im trying to use metrics to keep the same bitterness perception. Thanks again, I'll definitely look at this article.

 

[dmtaylor]

Specific gravity is one of the variables in many IBU calcuations such as Tinseth. Solubility of isomerized alpha acid decreases with increasing gravity. That's why you're seeing this effect.

Another VERY important tidbit: There is a maximum amount of isomerized alpha acid that can dissolve in the beer, and thus a maximum amount of IBUs you can have in a beer. By most measurements, the maximum is approximately 90 IBUs. So if your adjusted recipe is calculating 91 IBUs, you are right on the nose using the right amount, and if you used any more, you wouldn't gain any more IBUs from it anyway, point of diminishing returns. You could use 5 times as much hops and still end up with 90 IBUs. So, do as you have planned and you'll be in great shape.

 

[wepeeler]

Context: I brewed an american IPA which had an OG of 1.064 and calculated IBUs of 77.9 (including whirlpool additions). The beer turned out great and did very well in comps. Now Im wanting to scale this up to a double IPA with an OG of 1.075, and Im seeing some things that Im getting confused about. Ideally, I want the same percieved bitterness as my American IPA was. I use Beersmith. What beersmith is showing me is if I simply up the OG from 1.064 to 1.075 and don't keep the IBU level (ie the absolute volume of hop additions remains the same ) the BU:GU ratio obviously drops from 1.210 to 0.958 BUT the calulcated IBUs also drops to 71.8. So as OG increases and hop additions are unchanged, the calculated IBUs also goes down. was always under the impression that if you put a 60minute addition of a hop in for 20IBUs, this should still be 20IBUs regardless of gravity but the BU:GU ratio will obviously go down with increasing gravity. So beersmith seemingly adjusts the absolute IBU level when gravity changes but hop additions stay the same. If I target the same BU:GU ratio of 1.210 from my american IPA (OG 1.064) and adjust my double IPA (OG 1.075) to achieve the same ratio, my IBUs for the double IPA will be 91.3.

Concern/Question: I'm not sure if I should focus on upping the absolute IBUs vs the BU:GU ratio to accomplish this. These two variables seem to not be linear with each other. Will targetting the same BU:GU ratio really leave the perceived bitterness when drinking the beer the same? This is my goal: up the OG and keep the same perceived bitterness. Seems there are multiple moving parts here and me not knowing WHY Beersmith (or likely other calculators) lowers the absolute IBU level when gravity increases is a bit of a mystery to me. So BOTH the BU and GU change at the same time and not one staying the same while the other changes.

Now I will shamelessly tag others who have given me great advice on HBT but others are also and always welcome to chime in... @Dgallo @wepeeler @secretlevel @ihavenonickname

The best way I can explain it, as to MY understanding of IBU, would be to say as SG/OG increases, the calculated and perceived IBU go down, if you're using the same amount of hops. You have more sugar in suspension throwing off the balance if you used the same amount of hops at 1.064 vs 1.075.

In order to keep the BU:GU ratio the same you would need to add more hops as the SG increases. I believe the ratio is linear, but I could be wrong.

 

[ihavenonickname]

Specific gravity is one of the variables in many IBU calcuations such as Tinseth. Solubility of isomerized alpha acid decreases with increasing gravity. That's why you're seeing this effect.

I agree, this is the key point. The IBU calculators use wort gravity as an input for hop utilization.
If you care for math, this breaks down the different formulas.
https://homebrewacademy.com/ibu-calculator/#:~:text=Average%20IBU's%20%3D%20(Tinseth%20%2B%20Rager,with%20some%20real%20word%20examples.

So a way of thinking about it: your hops have to work harder against a more concentrated wort to achieve the same calculated IBUs. And keep in mind, you are at the limits of how helpful these calculators can be, so I agree with your plan to increase the hops to increase the IBUs to maintain your GU:BU. but more importantly: brew, taste, and verify.

Also, GU:BU gets a lot of attention (and that’s fine) but I think a somewhat overlooked variable is FG. I might even argue FG:IBU is more relevant to perceived bitterness. A 1.008FG 60IBU beer has much more perceived bitterness than a 1.012 FG 60IBU regardless of the OG

edit@Noob_Brewer

 

[Miraculix]

I agree, this is the key point. The IBU calculators use wort gravity as an input for hop utilization.
If you care for math, this breaks down the different formulas.
https://homebrewacademy.com/ibu-calculator/#:~:text=Average%20IBU's%20%3D%20(Tinseth%20%2B%20Rager,with%20some%20real%20word%20examples.

So a way of thinking about it: your hops have to work harder against a more concentrated wort to achieve the same calculated IBUs. And keep in mind, you are at the limits of how helpful these calculators can be, so I agree with your plan to increase the hops to increase the IBUs to maintain your GU:BU. but more importantly: brew, taste, and verify.

Also, GU:BU gets a lot of attention (and that’s fine) but I think a somewhat overlooked variable is FG. I might even argue FG:IBU is more relevant to perceived bitterness. A 1.008FG 60IBU beer has much more perceived bitterness than a 1.012 FG 60IBU regardless of the OG

edit@Noob_Brewer

I agree and I would even go one step further. It is not only the fg that really determines the final sweetness, but also the amount of alcohol and the amount of glycerol. Yeasts like belle saison for example produce high levels of glycerol which compensates for almost no sugars left after belle has done it's job.

I do not like this OG/IBU thing at all, there are way too many factors that are overlooked with this simplification.

 

[Noob_Brewer]

These are all great comments everyone! Thanks for your input. This is very helpful.

 

[G_robertus]

Why not think of an entirely different product? Depending on your recipe and how you scale it, you might want to address different factors. If you just increase base malt, you could probably just scale up your 60 minute addition proportionally to match your OG/FG change (I don't believe in OG for balancing bitterness solely). If you've scaled the entire recipe and you also add caramel malts, you might want to increase it a bit more to compensate for them. But like I said, this is something entirely different so you could also look at your late and especially dry hops. Alcohol increases the solubility of many hop compounds, so you could try to work in more. Alcohol also carries a flavour that you want to balance out, either with bitterness or malt/hop flavour. There's also the IBU ceiling you could hit and that also gets more difficult to reach with increasing OG, so you might need to compensate for that with late/dry additions.