Bag vs free.

Okay, so we all know that Alpha Acids isomerize through an acyloin-type ring contraction and turn into epimeric isomers; cis-isocohumulone, trans-isocohumulone, cis-isoadhumulone, trans-isocohumulone, etc. And the cis- derivitaves are the most stable, so that's what we typically taste for bitterness in the finished wort/beer. And top that with some kinetics data to determine that if your solution and conditions are wacky enough to promote boiling under 100c, you likely won't be getting enough hop utilization: for example, in a study at OSU regarding hop utilization at 70c and 120c, in a 90 minute boil only 10% hop utilization occurs at 70c, whereas at 120c 90% hop utilization occurs (Malowicki, and Shellhammer).

So after using a hop spider for some time and noticing no difference in my utilization, I have to wonder; why does the idea persist that bag hop utilization suffers in comparison to loose hops? When utilization of methylxanthines (caffeine, etc) is compared in tea in loose vs bag form (Hicks, Hsieh, and Bell 325-330), bag extraction was roughly twice that of loose extraction. There is a difference between alkaloid extraction and aa extraction, but the methods of extraction and rates of utilization are both quite similar.

So I ask you; is there any evidence that, when done properly, isomerization and hop utilization suffers in a bag or hop spider? I am defining properly as:
A). Hops not over-packed
B). Clean wort without excessive break matter
C). PH of wort not out of balance

If there are any reliable (id est, not colloquial, but a well performed study with reliable control) studies done in this vein I would love to read them. I am absolutely certain that there is a wealth of anecdotale information in the form of "I done brewed two and one tasted less bitter.", however I'm actually trying to put together something reliable and citeable; maybe even write an article on it.


Works Cited:
Hicks, Monique B., Peggy Y.H. Hsieh, and Leonard N. Bell. "Tea preparation and its influence on methylxanthine concentration." Canadian institute of food science and technology. 29.3-4 (1996): 325-330. Web. 26 Jan. 2013. <http://www2.hcmuaf.edu.vn/data/lhquang/file/Tea1/Tea preparation and its influence on methylxanthine.pdf>.
Malowicki, M.G., and T.H. Shellhammer. "17F-13 Isomerization kinetics of hop bitter acids during wort boiling ." Institute of Food TEchnologists. Oregon State University, 16 Jul 2004. Web. 26 Jan 2013. <http://ift.confex.com/ift/2004/techprogram/paper_25787.htm>.

I agree that with proper freedom of hop and wort, there should be little impact on hop utilization and isomerization. But there is a definite reduction in utilization when hops are either constrained in a somewhat tight hop sack or in whole hops. There are plenty of brewers that do encase their hops in a too constraining sack.

Just like the case where you HAVE to have a rolling boil to move the hop particles around the kettle to get proper hop utilization, allowing the hops to move about in a loose and permeable 'zone' is desirable too. That is the beauty of a hop spider.

When properly executed, the bag is free and billowing in the wort and the hops are just enjoying the ride, all over the zone. They aren't tied up or constrained. I believe you are correct that utilization does not suffer in that case. I think the perception that bagging your hops reduces hop utilization is from those cases of using a too tight a sack that doesn't allow the hop particles proper and complete contact with the wort during the boil.

PS: I've had extensive conversations with Mark Malowicki about this subject and his research. You use the term hop utilization above. That is not really what's being discussed in that research. He starts with alpha acid in solution and measured the degree of isomerization, not utilization. But I get what you are trying to say.

I take my hop bag out a couple of times during the session to let it drain. At the end I hang it by two corners from the top of my pot so it will drain as I transfer the wort. Seems to work well for me.

Another possibility (not tested, obviously) is that the hop spider allows the hops just enough movement to flow freely, but also holds the hops relatively still against the brownian motion of the water. When the hops are borne in the wort they are moving around, but the molecules carrying them move relatively close, potentially minimizing surface contact.

Yes, you are correct: Malowicki's research in this instance only dealt with isomerization at ideal temperatures and atmospheres, not utilization of the hops themselves.

I can see how using an overly tight sack would make utilization suffer (uh... No pun intended?). My personal and non technical opinion is; for a home brewer, a hop spider offers the best efficiency of process. When the brewing process becomes larger, the increase in hop efficiency (and reliability) makes it worth it to strain out the loose hop matter.

Mostly, though, thank you for a well thought out reply; I was hoping that I could elicit an intelligent response, and you've provided one.

Love this post. It should get more credit and see more eyes. Well done gentelmen, you guys just made my decision that I will use a hop spider instead of a hop stopper in my electric build I'm about to start. I was stuck on hop utilization potential issues with a 'bag' but now I see why that shouldn't be a problem (at least on the small scale level). And it seems to me the spider is the easier of the two hop seperation methods required for a plate chiller.

The only question remains: how tight is too tight for hop utilization to suffer?

My theory is that the resins easily flow out of the spider and the isomerzation occurs floating around the pot either way.

burntgraphite said:

Another possibility (not tested, obviously) is that the hop spider allows the hops just enough movement to flow freely, but also holds the hops relatively still against the brownian motion of the water. When the hops are borne in the wort they are moving around, but the molecules carrying them move relatively close, potentially minimizing surface contact.

Click to expand...

I'm not really sure what you're saying here, but I think under rolling boil the mixing (achieved by a combination of large scale flow and diffusion) is sufficient that a hop spider versus free hops will see little difference. The only danger I can imagine is a pocket of stagnant flow (that's an oxymoron, eh?) somewhere, like in a overpacked bag. The Brownian motion will basically be the same regardless of container geometry, size, or flow conditions because everything we're dealing with is on the millimeter or larger scale.

McCoy,
Hey, well said. After changing my brew process a bit, and experimenting with a few brews in both my Hop Spider and free-floating, I have found that a not-too-tightly packed hop spider does get apparently the same hop utilization as free floating. I brought two bottles of IIPA brewed from the same recipe, with only the one difference, to my BJCP group, and everyone had the same opinion; tastes the same. Of course, my IIPA recipe used a 5-gallon bag for the hop spider, so there were no flow issues.

Grathan,
That might be right; the isomerization doesn't happen on instant contact, so I guess that the AAs are isomerizing in the boil either way! With that in mind, as long as the hop sack isn't packed so tightly that it restricts the resins flowing out, you would likely get the same utilization either way.

Sorry to revive an old thread, but this is a good discussion. I too am curious as to whether the bagging versus free-floating effects hop utilization. There's quite a bit of anecdotal evidence floating around but I've been able to find no true research on this subject matter. If I had the wherewithal to purchase two TK2300 Test Kits, while producing the exact same recipe (with and without bagging), I'm sure that would put an end to this debate. However, my equipment doesn't lend itself to producing a precise replicate...that and spending $74 to put this to rest is a bit much =)