thecebruery
Active Member
I just brewed a relatively highly hopped (4 lbs/bbl, with 2 lbs coming as late and whirlpool additions and 1.5 lbs as dry hop additions) pale ale (1.055 OG). Mainly Galaxy (14.2% AA) all around, but rounded out with a some Cascade and Centennial (7.0% and 9.4% AA, respectively) during the boil and some Centennial in the whirlpool.
My question is about the methodology I used to calculate the IBU additions from my late and whirlpool additions and what other people do. First, a note on process: I do a ten minute pump circulation to start my whirlpool, during which time my kettle loses about ten degrees; I then let everything whirlpool and settle for an additional thirty minutes, during which time my boil kettle loses approximately 10F every ten minutes. That is, my temperature drops to approximately 200F while circulating, and down to 170F by the end of my whirlpool, at which time I begin chilling. I don't begin adding whirlpool hops until the temperature has dropped below 200F.
I've scanned old posts and read a few research articles and it seems estimates for hop utilization at these lower temperatures range from 10 - 15% between 200F and 212F, 5 - 10% between 190F and 200F, and 0 - 5% between 180F and 190F. Pretty much negligible below 180F. Obviously dependent on pH and OG.
Initially, I didn't even bother with these calculations - these utilizations seemed low, the amounts I was using didn't strike me as over the top enough to warrant the time, etc. Turns out it is worth the time - my first batch was far too bitter, and after doing the calculations (assuming I did them correctly), I see that nearly 1/3rd of my IBUs were converted post-boil - a 50% increased in expected bitterness.
To estimate them, I created a spreadsheet that kept track of each hop addition--bittering charge, late additions, whirlpool additions--and attempted to estimate their contribution over each temperature/time range. For instance, a 14.2% AA Galaxy addition at 20 minutes gave me 21.9 IBUs between flameout-minus 20 and flameout. This is all my software tells me this hop contributes. But if I take that same addition and call it a a 30 minute addition, Beersmith tells me that that same quantity of Galaxy would yield 27.8 IBUs, or an additional 5.9 IBUs. I simply took that additional IBU contribution (here, 5.9 IBUs) and multiplied it by the average utilization for that first ten minute temperature window after flameout (between 200F and 212F, an average of 12.5%, as a ratio to full utilization of 33%), and calculated that that particular Galaxy addition would give me an additional 2.2 IBUs during that ten minute period. Great. Changing that same addition to a 40 minutes in Beersmith gives me an estimated 31.8 IBUs ... but as I'm only interested in the extraction potential of the "next ten minutes," 31.8 IBUs minus the last 2.2 IBUs (extracted during minutes 0 - 10 while the kettle was dropping from 212 to 200F) minus the original 21.9 IBUs extracted during the boil, multiplied by the average utilization between 190F and 200F of 7.5% again as a ratio to full utilization of 33% gives me an additional 0.9 IBUs, and so on and so forth.
To briefly summarize the math, I calculated an additional 7.6 IBU contribution from the bittering charge + the late additions during the ten warmest degrees (212F down to 200F). An additional 7.8 IBUs came during the next ten minutes/degrees from 190F to 200F - obviously the utilization is lower and the extraction potential from the previous additions is diminished, but 200F is when I start adding my whirlpool additions, giving fresh potential back to the batch. By the time it's dropped to 190F, I calculated only an additional 3.5 IBUs during the final ten minutes of my whirlpool, between 180F and 190F.
Adding all those numbers together though gives me 18.9 IBUs that my software--which told me I would have IBUs around 34--didn't account for. Some of the numbers are definitely too big to ignore - an additional 7.6 IBUs as the wort cools to 200F (and that's before ANY whirlpool additions, which shows the importance of cooling quickly if you want to lock in your bitterness level), and an additional 7.8 IBUs during the first ten minutes of the whirlpool with a moderate whirlpool addition (1.8 IBUs of which come from the whirlpool addition, 16g of Galaxy, if you wanted to convert it to 5 gallon frame of reference, and the other 6 IBUs coming from the late hop additions added during the boil still lingering).
So, does this methodology seem sound to everyone? Am I misunderstanding the reaction kinetics of alpha acid isomerization? Does it back up experiences other people have had? Or does it sound like I'm relying too much on the math, and--if I were to back off my recipe to the tune of 19 IBUs (or shift my bittering charge and late additions forward even later to cut back on the IBUs while also increasing flavor and aroma)--I could end up with a crappy, overly sweet beer if I were to make adjustments based on this?
I understand that bitterness utilized at this temperature might taste different and a lot of these utilization numbers are just estimates and I need to experiment to get things right and yada yada yada. But for styles that rely less and more on hop flavor and aroma and less on bitterness like the new crop of pale ales and session IPAs that we all know and love now, being able to calculate the contribution from these late additions with some degree of precision would give us the ability to use our hops far more efficiently.
My question is about the methodology I used to calculate the IBU additions from my late and whirlpool additions and what other people do. First, a note on process: I do a ten minute pump circulation to start my whirlpool, during which time my kettle loses about ten degrees; I then let everything whirlpool and settle for an additional thirty minutes, during which time my boil kettle loses approximately 10F every ten minutes. That is, my temperature drops to approximately 200F while circulating, and down to 170F by the end of my whirlpool, at which time I begin chilling. I don't begin adding whirlpool hops until the temperature has dropped below 200F.
I've scanned old posts and read a few research articles and it seems estimates for hop utilization at these lower temperatures range from 10 - 15% between 200F and 212F, 5 - 10% between 190F and 200F, and 0 - 5% between 180F and 190F. Pretty much negligible below 180F. Obviously dependent on pH and OG.
Initially, I didn't even bother with these calculations - these utilizations seemed low, the amounts I was using didn't strike me as over the top enough to warrant the time, etc. Turns out it is worth the time - my first batch was far too bitter, and after doing the calculations (assuming I did them correctly), I see that nearly 1/3rd of my IBUs were converted post-boil - a 50% increased in expected bitterness.
To estimate them, I created a spreadsheet that kept track of each hop addition--bittering charge, late additions, whirlpool additions--and attempted to estimate their contribution over each temperature/time range. For instance, a 14.2% AA Galaxy addition at 20 minutes gave me 21.9 IBUs between flameout-minus 20 and flameout. This is all my software tells me this hop contributes. But if I take that same addition and call it a a 30 minute addition, Beersmith tells me that that same quantity of Galaxy would yield 27.8 IBUs, or an additional 5.9 IBUs. I simply took that additional IBU contribution (here, 5.9 IBUs) and multiplied it by the average utilization for that first ten minute temperature window after flameout (between 200F and 212F, an average of 12.5%, as a ratio to full utilization of 33%), and calculated that that particular Galaxy addition would give me an additional 2.2 IBUs during that ten minute period. Great. Changing that same addition to a 40 minutes in Beersmith gives me an estimated 31.8 IBUs ... but as I'm only interested in the extraction potential of the "next ten minutes," 31.8 IBUs minus the last 2.2 IBUs (extracted during minutes 0 - 10 while the kettle was dropping from 212 to 200F) minus the original 21.9 IBUs extracted during the boil, multiplied by the average utilization between 190F and 200F of 7.5% again as a ratio to full utilization of 33% gives me an additional 0.9 IBUs, and so on and so forth.
To briefly summarize the math, I calculated an additional 7.6 IBU contribution from the bittering charge + the late additions during the ten warmest degrees (212F down to 200F). An additional 7.8 IBUs came during the next ten minutes/degrees from 190F to 200F - obviously the utilization is lower and the extraction potential from the previous additions is diminished, but 200F is when I start adding my whirlpool additions, giving fresh potential back to the batch. By the time it's dropped to 190F, I calculated only an additional 3.5 IBUs during the final ten minutes of my whirlpool, between 180F and 190F.
Adding all those numbers together though gives me 18.9 IBUs that my software--which told me I would have IBUs around 34--didn't account for. Some of the numbers are definitely too big to ignore - an additional 7.6 IBUs as the wort cools to 200F (and that's before ANY whirlpool additions, which shows the importance of cooling quickly if you want to lock in your bitterness level), and an additional 7.8 IBUs during the first ten minutes of the whirlpool with a moderate whirlpool addition (1.8 IBUs of which come from the whirlpool addition, 16g of Galaxy, if you wanted to convert it to 5 gallon frame of reference, and the other 6 IBUs coming from the late hop additions added during the boil still lingering).
So, does this methodology seem sound to everyone? Am I misunderstanding the reaction kinetics of alpha acid isomerization? Does it back up experiences other people have had? Or does it sound like I'm relying too much on the math, and--if I were to back off my recipe to the tune of 19 IBUs (or shift my bittering charge and late additions forward even later to cut back on the IBUs while also increasing flavor and aroma)--I could end up with a crappy, overly sweet beer if I were to make adjustments based on this?
I understand that bitterness utilized at this temperature might taste different and a lot of these utilization numbers are just estimates and I need to experiment to get things right and yada yada yada. But for styles that rely less and more on hop flavor and aroma and less on bitterness like the new crop of pale ales and session IPAs that we all know and love now, being able to calculate the contribution from these late additions with some degree of precision would give us the ability to use our hops far more efficiently.