Hops Education Please

[BrewerBS]

I have been reading some posts about how your boil size can affect your IBU. I have found that utilization drops considerably when only doing a 2gal boil vs a full boil. Is this true? Is there a way to maximize utilization when only doing partial boils? Is it different if I only have a 2 gal boil but rack the entire pot, including all the hop trub from the bottom of the kettle when I put it in my primary? Does keeping those hops involved after the boil is over help to increase the utilization at all? Don't want to waste those hops if I don't have to!


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[GrumpySquirrel]

I don't have any proof outside of experience and the countless tales I've read from others (who have proof). But, yes, full boil will better utilize hops than a half boil. It just means that if you are doing an extract kit that uses 1 oz of hops, it will extract more acids in a 6 gallon boil than in a 3 gallon boil.

 

[BWE]

Look at it like this... When you brew coffee, you don't add half coffee to your cup and then half water. I don't know the scientific explanation... but that's my lamens one.

 

[Kealia]

As the gravity in your wort increases, hop utilization decreases.

What you can do to offset a partial boil is add a god majority of your extract late in the boil (the last 5-10 minutes). This keeps your gravity low, increases your hop utilization and prevents your extract from darkening or going through a bigger Maillard reaction than you intended. This prevents the extract from carmelizing too much, which can also lead to issues with under attenuating.

Most brewing software will allow you to designate a late addition of extract. Are you using any software now?

 

[IslandLizard]

The literature claims that hop utilization depends on the gravity of your boil. So a 2 gallon boil and a 6 gallon boil of the same gravity should yield the same AA conversion after an hour.

That is one of the reasons you should not boil your whole extract bill from the get go (causes high gravity, as well as darkening and potential scorching). Boil only 1/2 or 1/3 and add the remainder at flameout.

Now if you added a large load of hops I would expect to see utilization differences between smaller and larger volumes, based on hop oils density/concentration.

 

[Yooper]

IBUs don't depend on wort gravity, although it was previously thought so.

What does impact the IBUs is simple dilution and the fact that hops oils have a maximum amount of isomerization before being saturation, generally about 100 IBUs at a max (and even that is unlikely, according to studies).

So, say you have 2.5 gallons of 90 IBU wort. You need to top it up with 2.5 gallons of 0 IBU water. That means a maximum of 45 IBUs in the beer. That's fine in many beers, but not beers like IPAs and that is the limiting factor in these brews done by a partial boil.

We talked more about this the other day in this thread: https://www.homebrewtalk.com/f12/ipa-recipe-sanity-check-461744/

 

[IslandLizard]

Look at it like this... When you brew coffee, you don't add half coffee to your cup and then half water. I don't know the scientific explanation... but that's my lamens one.

Neither should you boil your coffee nor add hops.

 

[IslandLizard]

IBUs don't depend on wort gravity, although it was previously thought so.

What does impact the IBUs is simple dilution and the fact that hops oils have a maximum amount of isomerization before being saturation, generally about 100 IBUs at a max (and even that is unlikely, according to studies).

So, say you have 2.5 gallons of 90 IBU wort. You need to top it up with 2.5 gallons of 0 IBU water. That means a maximum of 45 IBUs in the beer. That's fine in many beers, but not beers like IPAs and that is the limiting factor in these brews done by a partial boil.

We talked more about this the other day in this thread: https://www.homebrewtalk.com/f12/ipa-recipe-sanity-check-461744/

Although you're correct (sort of), that thread is not an eye opener or proof that wort gravity does not influence hop utilization. The concentration of dissolved or suspended molecules in a solution or medium influences chemical reactions, exponentially more so the higher those concentrations.

 

[IslandLizard]

To answer the second part of your question, many brewers do not see any problem heaving the hops and break matter (trub) into the primary fermentor. Others want to transfer as cleanly as possible, one reason being to harvest the yeast later. The consensus is the trub does not cause off flavors later on. So do what works best for you.

I know it feels wasteful to dump all those hops in the compost pile, particularly the ones you added late in the boil. At those temperatures the hop oils dissolve quickly into the wort, but you'll get more bang for your hop buck to leave them in for say 20-30 minutes after you turn off the heat (hop stand, hop steep). Stirring the hopped wort (or whirlpooling) helps in that extraction process.

ADDED: Using a larger pot allows you to boil larger volumes as long as your heat source (stove?) can provide you with a rolling boil (not just a simmer). Most stoves peter out at 4-5 gallons. YMMV.

Nothing prevents you to split the boil over more than one pot. I still do that. Then combine the 2 chilled batches in your fermentor and top up with whatever water it needs to get your target volume.

Hint:
Put a volume marker on your fermentor before pouring. It is oh so hard to determine the volume once the wort is in there.

 

[Yooper]

Read some of the latest statements from John Palmer and others. Basically, John says he "got it wrong in How to Brew", and that IBUs are indeed independent of wort gravity although the IBU calculators still use the old formulas which do include the wort gravity in the calculations.

Of course, those calculators are known to be incorrect. Even Pliny the Elder, which calculates on the Rager scale at something like 250 IBUs, has been actually tested at something like 85 IBUs. Not even close- and not exactly accurate.

John told me that gravity does not affect IBUs (although perhaps break material does) in about 2008, and he presented some data at that time at the NHC, but I know he's done some talks on things like Basic Brewing Radio (that one called "What is an IBU, really?") if you want to listen to a podcast instead of reading through a bunch of somewhat obscure papers.

 

[IslandLizard]

Read some of the latest statements from John Palmer and others. Basically, John says he "got it wrong in How to Brew", and that IBUs are indeed independent of wort gravity although the IBU calculators still use the old formulas which do include the wort gravity in the calculations.

Of course, those calculators are known to be incorrect. Even Pliny the Elder, which calculates on the Rager scale at something like 250 IBUs, has been actually tested at something like 85 IBUs. Not even close- and not exactly accurate.

John told me that gravity does not affect IBUs (although perhaps break material does) in about 2008, and he presented some data at that time at the NHC, but I know he's done some talks on things like Basic Brewing Radio (that one called "What is an IBU, really?") if you want to listen to a podcast instead of reading through a bunch of somewhat obscure papers.

Thank you Yooper, I'm sure not the only one not being aware of this later research debunking existing hop utilization knowledge. Many people and programs still use these tables with great success apparently.

Maybe the models and formulas by Tinseth, Garetz and Rager hold up for lower hop oil concentrations, but divert largely in today's quest for creating the ultimate hop bomb. Who could have predicted brewers would be dumping half a pound of hops or more into a 5 gallon batch on purpose? That's just crazy! And yummy.

Let's hope something sensible can be calculated or estimated at some point. Modern day brewing is cutting edge!

 

[BrewerBS]

As the gravity in your wort increases, hop utilization decreases.



What you can do to offset a partial boil is add a god majority of your extract late in the boil (the last 5-10 minutes). This keeps your gravity low, increases your hop utilization and prevents your extract from darkening or going through a bigger Maillard reaction than you intended. This prevents the extract from carmelizing too much, which can also lead to issues with under attenuating.



Most brewing software will allow you to designate a late addition of extract. Are you using any software now?

I am not currently using any software. I only have a 4 batches under my belt and have only brewed extract kits so far. I was just reading in some of the comments about the kit that I had purchased that the IBUs drop dramatically when you only do a 2 gal boil. Just looking for a reason to get that new bigger pot!





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[BrewerBS]

IBUs don't depend on wort gravity, although it was previously thought so.



What does impact the IBUs is simple dilution and the fact that hops oils have a maximum amount of isomerization before being saturation, generally about 100 IBUs at a max (and even that is unlikely, according to studies).



So, say you have 2.5 gallons of 90 IBU wort. You need to top it up with 2.5 gallons of 0 IBU water. That means a maximum of 45 IBUs in the beer. That's fine in many beers, but not beers like IPAs and that is the limiting factor in these brews done by a partial boil.



We talked more about this the other day in this thread: https://www.homebrewtalk.com/f12/ipa-recipe-sanity-check-461744/

Thanks for the link!


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