Gravity effects on hop stand utilization

[CHansen6]

I feel like this should be a relatively simple issue, but I can't seem to find a definitive answer.

I'm looking to do a hop stand on a beer I'm formulating. From what I've read I'm seeing values somewhere between 10-15% hop utilization, or being equivalent to X minute boil. All of these things will be dependent upon exposure time and temperature of course.

I'm wondering what influence gravity has on this. I would think that just like boiled hops, the utilization of the hop stand would proportionally go down.

I've also seen estimates of approximately 1/2 the boil duration utilization for a hop stand at 190F. IE, a 30 minute hopstand for 1.060 wort has about 8.1% utilization compared to 16.2% for a boil. This is what Beersmith uses at least.

I understand there are more factors at play here, but would using the 1/2 utilization compared to boil, and figuring in the appropriate utilization based on gravity be the best ball park?

 

[EternalStudent]

What is a "hop stand"?


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[EternalStudent]

I looked it up. I think you are referring to a whirlpool addition, guess I haven't heard anyone use that terminology before.

I set my whirlpool additions to 5 min additions in beer tools and that covers the utilization pretty well. Depending on the ambient temp you won't be converting too much longer after the temp drops from a boil.


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[WoodlandBrew]

I'm actually working on an article that sounds like it may help answer your question. The rate of Alpha-acid isomerization is an exponential function of temperature, and there is very little conversation south of boiling, however hops already contain some isomerized alpha-acids, so you will get some bittering there. The other flavor contributions are relatively independent of temperature. Jaskula [1] determined the rate constant over the temperature range of 80°C to 100°C (176ºF to 212°F) From this the relative rate of isomerization (to boiling) can be derived at the temperature in question.

Fahrenheit  Celsius  Kelvin  relative to boiling
212°F       100°C    373°K   100%
210°F       99°C     372°K   91%
200°F       93°C     366°K   57%
190°F       88°C     361°K   35%
180°F       82°C     355°K   21%
170°F       77°C     350°K   12%
150°F       66°C     339°K   4.2%
100°F       38°C     311°K   0.2%
75°F        24°C     297°K   0.03%
70°F        21°C     294°K   0.02%

[1] 2008, A Kinetic Study on the Isomerization of Hop alpha-acids

 

[WoodlandBrew]

I'm wondering what influence gravity has on (isomerization of alpha acids)

Whether specific gravity impacts alpha-acid isomerization depends on who you ask. Tinseth (1995. A home brewer who developed the equations that are used by most brewing software) found that gravity does have an impact on utilization. This is commonly accepted by homebrewers. However, Malowicki[1] (2005. Who has a Master of Science in Food Science and Technology) found that there is no correlation between gravity and hop utilization.
[1] 2005, Hop Bitter Acid Isomerization and Degradation Kinetics in a Model Wort-Boiling System

 

[CHansen6]

I appreciate the great information WoodlandBrew. I found Malowicki's thesis, and Jaskula's paper. I'll read through both of them, as well as some of the other references you mentioned.

I may just be thinking too much into it.

I am a chemist by trade with free reign on most analytical equipment. It wouldn't be hard to generate a little data for myself either.

 

[WoodlandBrew]

I'm glad you were able to find those papers. I'm sure you'll be able to get more out of the papers than what I have gleaned from them. If you do decide to do some of your own experiments I would love to hear about them, and I'm sure others here would as well!