Leaf Hop Absorption Measured

**ChemE** · 04-22-2011, 11:27 PM

I have searched this topic several times over the last three years and I've always been shocked and disappointed with the lack of careful measurement regarding this topic. I'm brewing a barleywine tomorrow with an OG of 1.120 and five ounces of whole leaf hops (it's just a 3 gallon batch) so I'm very interested in how much of my precious barleywine those pesky hops are going to drink up.

I decided to conduct a simple stove-top experiment to get a number. 0.39 ounces of 2008 cascade hops sacrificed themselves for our collective knowledge. Below is the simple setup consisting of a hop bag, the cascade hops, a small pot of water, and of course a gram scale.

Experimental Setup

I wanted to make the amount of water that the hop bag absorbed a non-issue, so I soaked it in the boiling water for a minute and then hung it by its drawstring for two minutes to allow it to drain. This is how I drain my hops over the boil kettle while I chill. The damp/wet hop bag had a mass of 28 grams.

Wet/Damp Hop Bag Being Weighed

Next step was to add the hops (but not the oxygen absorber!) and boil for 20 minutes. I assume this is long enough for them to absorb what they can but this is an assumption. After their boil, I hung the bag from the drawstring again for two minutes to simulate draining over the boil kettle. I did not squeeze the bag since it is claimed that this extracts tannins (another theory which wants to be tested).

Hops Being Drained for Two Minutes via Gravity

Wet/Damp Hops Being Weighed

So, the final mass is 93 grams less the 28 grams for the wet hop bag and less 11.1 grams for the dry hops yields a mass increase due to water absorption of 54 grams. Scaling this up from 0.39 ounces of hops to a full ounce takes us to 138.3 grams of water gain or 138.3 mL of water absorbed. The converts to 0.146 quarts of water per ounce of whole leaf hops. My data appears below.

Data and Calculations

Some assumptions and sources of error:
1) I assume that 20 minutes is sufficient to completely hydrate the hops
2) I assume that tap water goes into the hops just as readily as sweet wort
3) I assume that the specific gravity of the water that went into the hops is 1.00
4) All weights taken on a gram scale so precision could be higher

I think these assumptions are safe and the source of error minimal. Overall I trust this number but certainly welcome feedback or suggestions. I hope the community finds this useful.

shauntraxler · 04-23-2011, 07:29 AM

Seems solid to me. Nice write-up.

Dogphish · 04-23-2011, 12:16 PM

i don't think that squeezing the hops will extract tannins. i believe that only the grains have tannins that you should worry about. i asked that exact question on this forum before, and that was the general consensus.

cjb · 04-23-2011, 09:48 PM

Quote:

Originally Posted by Dogphish

i don't think that squeezing the hops will extract tannins. i believe that only the grains have tannins that you should worry about. i asked that exact question on this forum before, and that was the general consensus.

Yeah, I had the same misconception, based on warnings against squeezing the grain bag. Asked on another forum, and was told it's not an issue for hops.

timbudtwo · 04-23-2011, 10:03 PM

Quote:

Originally Posted by Dogphish

i don't think that squeezing the hops will extract tannins. i believe that only the grains have tannins that you should worry about. i asked that exact question on this forum before, and that was the general consensus.

You can squeeze grains too. It doesn't release tannins, high temperatures do. That was an old brewers-wife tale.

http://www.homebrewtalk.com/f36/do-you-squeeze-bag-biab-177051/

**ChemE** · 04-23-2011, 10:55 PM

Hmm, now I wish I had gone a step further and wrung the heck out of the hop bag after I let it gravity drain. I'll perform that measurement next week when I get back in town (business travel).