I know there's been a lot of discussion in the homebrew meetings about the effects of "hot-side aeration". Here's the meat of the subject: Oxygen can bond itself molecularly onto many things (of which in class we haven't discussed) in the wort AND the crushed grain. I'm assuming it bonds with amino acids, peptides and other long-chain proteins like b-glucane that are soluble but unfermentable in wort. (Help me out bio-chemists!)
There is an enzyme developed in barley, that is prevalent in well-modified malt, called LOX or lipoxygenase. Just like it sounds, it digests lipids in the presence of oxygen. Most home, craft and micro-brewers don't even bother with the level of LOX- you can't measure it, you can only prevent it. It causes beer staling(oxidation), and in some cases gushing, in a frosty brew. I don't yet understand how it works, enzymes are ALL denatured at boiling temps, but LOX obviously can ruin a finished beer.
So, you can aerate your mash and crushed your dry grains all you want as long as your product is consumed within a month of manufacture. Large breweries go to great lengths to ensure that oxygen cannot expose the mash bed or the crushed grain. Many large breweries have wet malt mills: mills that crush wet malt to ensure no exposure to oxygen.
Anybody want to weigh in on this one? I'll ask Ray Daniels tomorrow and I won't leave until I have a bio-chemical answer.
Subscribe to:
Post Comments (Atom)
Posts
5 comments:
I always refer back to this article written years ago.
http://www.brewingtechniques.com/library/backissues/issue1.4/miller.html
Wow, you're taking me back to beta oxidation. By definition reduction/oxidation is addition or subtraction of electrons, and in biology usually O2 is the major acceptor of electrons. So from what I know, most oxidative metabolism that you and I do (of lipids, etc.) occurs through oxidative phosphorylation (wikipedia if you want). In that case you transport all of your e to one place and pretty much have only one complex that sticks to O2 or actually uses elemental oxygen (O2). Now onto Kevin'c question. Lax would be analogous to globin in your blood. It uses iron in the protein to coordinate O2 so that it can do its job as an enzyme. These iron clusters are held together by chemical bonds. ... and it's these iron groups that bind O2 (or "stick' as you say). When you denature proteins you "unfold" the protein, i.e. ruin the structure of the strand of amino acids making up the protein by disruption of hundreds of internal hydrogen bonds (Hydrogen bonding is not a chemical bond - think of static cling making your clothes stick to your body). Denaturation by boiling doesn't destroy chemical bonds, so the iron containing elements will still stick to O2 even if the protein is denatured, possibly carrying the O2 into the wort. I surmise that only after the iron clusters are degraded and/or themselves reduced will they let go of the O2 letting it oxidise your beer. This may take ... oh, 1 month or so????
I just made all of that up but I believe it. Sorry for the dumbed down and/or smarted up geek talk.
Oh Boy, KC I don't have a clue what you're talking about. I really wish I did because that brain of yours in large and full of brewing knowledge. However, the link Colin gives is quite accurate.
Beer is full of anti-oxidants or "tannins" as the wine industry touts. These are long chain proteins that could accept oxygen. If they are exposed to oxygen early, like in the mash, then they don't have their great anti-oxidant quality. Also, since accepting the oxygen, they stales. Ray called this phenomena a "bugaboo" in the industry. How much it affects your beer depends on the shelf life you expect.
Nerd alert! Nerd alert! I'm glad I got into brewing because I sure as hell didn't pay attention in science class.
Yes, Colin's article explained it much better. Bottom line is that things get oxidized, and carry the O2 molecule through, even if they get denatured and then can release the O2 molecule, or themselves cause oxidation by giving up the O. I thought you were referring to Lox, specifically. However, it was fun to venture back into Biochem 507! :-)
Post a Comment