Improving precision in IBU calculations

[Lyrebird_Cycles]

I've become super lax about my additions of late - just going off guestimates and using my palate as a yardstick

Nothing wrong with that - it's how I worked out that the Tinseth calculator wasn't working for my conditions.

This is the old Excel spreadsheet I put together (about 10 years ago) it shows the interplay of the Alpha > Iso Alpha > Degradation.
Its basically equation 12 (with the sign reversed), it illustrates the conditions of the experiment, without any of the additions/modifications/improvements you have made.
Interesting work to date much appreciated.
Mark

IBU's.xls

I actually don't think the sign in Eq 12 is wrong, if it were Cdeg would move in the wrong direction over time.

As it stands the RHS of Eq 12 reads Calpha,initial + Calpha,initial / (rate terms) where any mathematician would have expressed that as
Calpha,initial ( 1 + 1 / (rate terms)).
Also at t = 0 the rate term exponentials are both = 1 so their difference = 0 and the rate terms disappear so as it stands or with your modification we would be left with C deg = C alpha, initial which makes no sense.

I believe the first Calpha,initial. term should be Cdeg,initial instead.

 

[Lionman]

I've become super lax about my additions of late - just going off guestimates and using my palate as a yardstick but understanding the mechanisms at work at this level of detail is fascinating.
Cheers for your work so far.

As a home brewer there is no real need to measure or calculate anything. You can do it all off guestimates and still get beer at the end of the process.

If you want to be able to consistently reproduce results, know an accurate ABV or reproduce a commercial beer as accurately as possible or improve efficiencies etc then it definitely helps to do it 'properly'.

There's nothing wrong with using experience as your guide though, as long as you like the beer at the end of it. Lots of people just brew to get beer and don't delve too deep into the technicalities.

 

[manticle]

My lax attitude is the result of many measurements, tweaks and getting to know ingredients, palate and how my system and process relates to that. Measuring has been important, understanding what those measurements really mean moreso.

 

[johnmeyers]

Hey there,
Just wanted to say thanks for all the effort you put into analyzing these papers and creating a user friendly IBU calculator that might be more accurate than anything else out there. Though the math is significantly above my head, I learned a lot in the process of going through your explanation!

I'm in SLC Utah, USA and bought a Picobrew Zymatic. I like the repeatability of the Zymatic, and focusing on the recipes/design instead of cleaning all day--I know it's a controversial device. Anyways, I stumbled upon this thread due to concerns about low hop utilization. I'm at about 1310 meters, but due to technical issues with the Zymatic, I can only "boil" at ~92.6c. For this reason I've set my "Altitude" in your spreadsheet to 2133--about where the boiling temperature would be 92.6. The Zymatic is a semi closed system so I've somewhat arbitrarily assigned it a low 3% boil-off rate (will have to measure this sometime when I can weigh pre/post boil) and 0% vigour, since it never technically boils (extra DMS is what I get for being lazy). Hopefully that all sounds reasonable.

The question I have for you is: the "boil" in the zymatic essentially dribbles wort over the hops--the whole volume of fluid is continually being washed over the hops in a given hop "cage". How do you think this would affect utilization? Technically, all of the wort is never in contact with the hops at any one point in time. But it is always flowing over it.

Lastly, when I cool my wort, it is completely removed from the hops--does the cooling calculation assume that the entirety of the hops are still in the wort when being cooled? Or is there continued hop utilization increase even if separate? Most of my hops will stay in the cage during cooling, separate from the wort, the mesh is quite fine.

As an aside: sweet wooden bikes. Based on how in-depth you get with beer, I'm strongly inclined to buy one from you--I bet they're fantastic. Can I presume you're the builder for those as well?

 

[Lyrebird_Cycles]

The question I have for you is: the "boil" in the zymatic essentially dribbles wort over the hops--the whole volume of fluid is continually being washed over the hops in a given hop "cage". How do you think this would affect utilization? Technically, all of the wort is never in contact with the hops at any one point in time. But it is always flowing over it.

I can't see any reason for that to have a significant effect on utilisation, if it did you could compensate by setting the "initial utilisation" number to something that gives you reasonable results; the 75% figure seems to work for many setups but it isn't set in stone.

Lastly, when I cool my wort, it is completely removed from the hops--does the cooling calculation assume that the entirety of the hops are still in the wort when being cooled? Or is there continued hop utilization increase even if separate? Most of my hops will stay in the cage during cooling, separate from the wort, the mesh is quite fine.

That's a really interesting one. The utulisation model on which the calculator is based assumes that the alpha acids are already present in the wort and tracks their conversion to isoalpha acids, so in theory removing the spent hops should have little effect. I am not certain that this assumption correlates 100% with the real world as it implies that all of the extraction happens as soon as the hops are added, which seems unlikely.

I think the closest approach would be to leave the cooling times in the calculation if the hops have been present thoughout the boil. For late throw hops you might need to shorten the cooling times.

As an aside: sweet wooden bikes. Based on how in-depth you get with beer, I'm strongly inclined to buy one from you--I bet they're fantastic. Can I presume you're the builder for those as well?

Thank you. Just to be clear, they are not entirely wood: I refer to the construction method as "Tonewood Composite" as the fibre composites are a significant contributor. And yes all the building is done by hand by me, including laying up the tubes.

You don't happen to be very tall do you? I'm looking for a tester who is 2 metres (6'7") or greater.

 

[johnmeyers]

Fair enough. A lot of variables in this equation! Thanks for taking the time to answer!

And I must say, you definitely make me wish I was a another 2 inches taller! I'm 195cm. I raced bikes for about 9 years, was a Category 1 (don't know the Aussie equivalent), and have ridden a lot of different bikes. I remember racing against Cameron Meyer/Clarke brothers/Jonathan Cantwell/Richard England/Bernie Sulzberger, and a bunch of other Aussie mates who'd come over to the states for Superweek back in the day. I think some were on team AIS Australia or Southaustralia.com? Good memories. Holler if you need someone 195cm or taller--I'm your man!

 

[idzy]

Thanks for the write up and links. Lots to read. Appreciate you taking the time.

 

[Lyrebird_Cycles]

OK, this took longer than expected; I had to add lots of logical decision trees so that hops added after flameout calculated correctly.

I think I've found all the glitches,if you find one I missed please post it.

View attachment Bitterness Calculator_V4.xlsx