HOMEBREW Digest #5639 Thu 31 December 2009

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  Oxidation and HSA by Bamforth on Brew Strong (Calvin Perilloux)
  Oxidation and HSA by Bamforth on Brew Strong - Part 1 (Calvin Perilloux)
  Oxidation and HSA by Bamforth on Brew Strong - Part 2 (Calvin Perilloux)
  Oxidation and HSA by Bamforth on Brew Strong - Part 3 (Calvin Perilloux)
  Oxidation and HSA by Bamforth on Brew Strong - Part 4 (Calvin Perilloux)

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---------------------------------------------------------------------- Date: Thu, 31 Dec 2009 07:28:22 -0800 (PST) From: Calvin Perilloux <calvinperilloux at yahoo.com> Subject: Oxidation and HSA by Bamforth on Brew Strong Back at the beginning of this month, AJ deLange highlighted an interesting interview about HSA (Hot Side Aeration) with Dr. Charles Bamforth on the Brew Strong broadcast: "everyone worries about it but the evidence doesn't seem to support its existence." This did pique my interest, but a podcast, ugh! Maybe it's me, but it seems so much easier to digest written material than to hear and remember all the details from a running conversation like the interview in question. I even tried listening to it on some long commutes, but after clearing hectic traffic spots I'd then realize that I'd been foolishly paying attention to the road and missing parts of the podcast! And at home, with howling kid and other distraction... well, never mind... So in the end, I wondered if other homebrewers have the same concerns that I did, and thus on one dark, snow-bound winter day, I buckled down with some fast typing and took notes on 50 minutes of Bamforth's wisdom. I will present these notes here shortly, as soon I get them checked for typos -- and as HBD accepts them, since I'm sure I can't post the whole set of notes in just one big posting. Enjoy. (Soon) Calvin Perilloux Middletown, Maryland, USA Return to table of contents
Date: Thu, 31 Dec 2009 07:56:24 -0800 (PST) From: Calvin Perilloux <calvinperilloux at yahoo.com> Subject: Oxidation and HSA by Bamforth on Brew Strong - Part 1 Oxidation, Staling, and Hot Side Aeration (HSA) An Interview with Dr. Charles Bamforth Source: Brewing Network's Brew Strong Broadcast, January 26th, 2009 http://www.thebrewingnetwork.com/shows/475 [Ed: This is a set of notes that I took while listening to podcast. I think most of the information here is accurate and mostly complete, but if you have the time, listening to the full broadcast will surely fill you in on more details and nuances that I didn't capture here. The Bamforth interview starts at about minute 16. The minute indicators shown below are approximate but should get you within 1 minute of the actual topic if you want to hear more details.] 16:00 The biggest technical challenge facing brewers today: Addressing flavor stability. 17:00 Attaining flavor stability is not like detecting and preventing haze where things are present in sizable quantities and easy to spot; with flavor instability it can be parts per billion, sometimes even parts per trillion. 18:00 Are there a few compounds that define stale beer character? Many, actually. One is nonenal, or trans-2-nonenal, or as chemists say (E)-2-nonenal, which is covered in most papers on the topic. This is "cardboard", but that's simplistic, since there can be cardboard flavors due to other things. Stale beer doesn't have to have nonenal to exhibit staleness; that's also simplistic, and there are lots of other carbonyls. Trans-2-nonenal contains a carbonyl compound, carbon linked to oxygen with a double bond. This group is present in numerous compounds in beer; there are tens or hundreds of them, some important, some less so. So it's not just nonenal we need to worry about. 20:00 Carbonyls give off numerous flavors and aromas, even including some like metallic. Other types (e.g. "aged character") are commonly found in aged beers. These can come from lots of sources. Oxidation of unsaturated fatty acids is the root; if you oxidize linoleic acid, that leads straight to (E)-2-nonenal. So lots of people say that's it, but other compounds can also break down into carbonyls, even alcohols. 21:00 Acetaldehyde is a carbonyl, and it's a precursor of alcohol in beer, but the reaction can go in the reverse as well. Hashimoto worked on oxidation of higher alcohols, and how it was sped up by melanoidins from Maillard reactions -- which conventional wisdom considers antioxidants! 22:00 Amino reactions break down in a Strecker reaction. Also one carbonyl can react with other compounds to form one with a much lower aroma/taste-threshold. Even hop alpha acid acids can break down to give carbonyls. 23:00 Does oxygen have to be part of the process? No. In terms of flavor change, it's more than just oxygen, but the oxidative state of the wort/beer that is important. It is Redox reactions, and an oxidizing system/environment can transfer that oxidative power. Oxidizing a polyphenol could conceivably pass on the oxidative power to something else later. Redox potential is what to consider, even though oxygen is the main thing we think of. Oxygen itself is not "desperately reactive" and often needs to be activated first (that is, given a mechanism) to do its damage. One is via enzymes; the other is via active forms called free radicals, which is where metal ions like iron and copper come in and promote the formation of radicals. 26:00 Superoxide, peroxide, hydroxyl (the most reactive) are the free radicals which are the real oxidative culprits. [to be continued...] Return to table of contents
Date: Thu, 31 Dec 2009 08:20:24 -0800 (PST) From: Calvin Perilloux <calvinperilloux at yahoo.com> Subject: Oxidation and HSA by Bamforth on Brew Strong - Part 2 [continued from Part 1] 27:00 To reduce oxidation and staling: Reduce air intake, cap on foam, but one area of controversy is avoiding hot wort aeration. What stages should we be aware of the potential for oxidation of amino acids and proteins that can later catalyze other reactions? Answer: "Who knows?" There is much research, controversy, and debate. There are a lot of stages in the malt to beer process, and whether HSA has a major effect on flavor stability is debatable. 30:00 Nobody argues that lower the free oxygen in the bottle, the better. But the beer still goes stale, even when oxygen is at a parts-per-billion level. So the blame gets passed by the brew upstream, back to the maltster for example, saying that malt can be predisposed to make stale beer! Barley can be bred to have some lower enzymes (lipoxygenase, aka LOX) like Clarity Malt, but there are still other reactions that cause a problem. You still have iso-alpha-acid and amino acid breakdown that you cannot avoid. 32:00 Lipoxygenase is heat-sensitive, so some people say to mash in high to prevent this enzyme from working. That is, come in at 65 C/149 F to reduce that potential. But even eliminating that enzyme, the oxygen can still react with non-saturated fatty acids, particularly if you have metal ions (think copper brewhouse). It also reacts with gel proteins to cross- link them; think of the top-dough on the mash. There are traces of hydrogen peroxide which are very active. Peroxidases will help that react with polyphenols, and those in turn stick to proteins and cause cloudy wort and increased color. So getting oxygen in the mash darkens the color. It also increases turbidity, which is actually good news later because you're precipitating these compounds out. But you also have ill-defined flavor changes taking place with oxidation at this point. 35:00 A real life example: He (Bamforth) was a quality manager at Bath [sic?] Brewery near Liverpool, brewing Carling Black Label. His brewery's Beers were the ones that they could identify every time as harsh and grainy. They cut down the amount of oxidation in the brewhouse. It didn't affect stability, but it did affect the flavor and improved it a lot; unfortunately, customers sent it back because they didn't like it any more! 37:00 They also tended to pay attention the vigor of the boil, balancing heat stress with purging of volatile components with an active boil. There are arguments that you can have oxidation in the mash, and by (yes!) promoting it then if you can get rid of the oxidized products by boiling and thus volatilizing them, so then you have a cleaner beer. The counter argument is that the more you heat, the more then risk of thermal damage. Bamforth et al tried ascorbic acid in the mash, which did totally nothing. They also tried SO2 (in metabisulfite form), which binds to carbonyl compounds and makes them non-flavorful. If the brewing industry was prepared to use that in the finished product, then it would work, but in the United States, if you have over 10 ppm then you have to label it on a commercial label. That apparently works fine for wine marketing, but beer customers won't stand for it. 41:00 By putting in SO2 upstream, though, you can reduce oxidation. But another example: One brewer did that in a commercial brewery and got "rotten egg beer". The yeast took it and made hydrogen sulfide. The initial brewery tests were in a plant with copper pipe, and copper and sulfite bind and thus egg flavor is avoided, but this fellow had nothing but stainless steel in his brewery, so the sulfite carried over to the fermentation. 42:00 Yeast is a hell of a good way to clean up stale flavors. Sluggish and poor fermentations, though, don't clean those up as well. An example of the reduction reactions is acetaldehyde reduced to alcohol by yeast. Yeast can even reduce nonenal. You can take stale beer and move it through an immobilized column of yeast, and the yeast will clean it up. So an argument can be made that oxidation in the brewhouse is irrelevant because yeast will clean it up. 44:00 An unnamed brewery [named later by someone else as maker of Budweiser] goes so far as to bubble air through hot wort in order to strip off DMS from their wort to make a more gently flavored product. That sounds completely counterintuitive to what most brewers would ever do, but that company and beer are the freshest in the world, North American Lager. Why does this work? Some carbonyls are being bubbled away; others are reduced later by vigorous, healthy yeast. [to be continued...] Return to table of contents
Date: Thu, 31 Dec 2009 08:36:01 -0800 (PST) From: Calvin Perilloux <calvinperilloux at yahoo.com> Subject: Oxidation and HSA by Bamforth on Brew Strong - Part 3 [continued from Part 2] 46:00 Would the temperature of the wort in this very-hot-wort aeration process, where the wort is near boiling, give different oxidative results than when it's 120-140 F? Lipoxygenase proponents would say that this would carry through and break down in the finished product. Bamforth is skeptical. 47:00 Other interesting arguments: These oxidative products are produced in the mash but are not reduced by the yeast because they stick on to other things. A woman in Lueven [unnamed research person] claims that these stick to proteins; others say SO2 that's already present in the mash does that. These oxidized components are then carried on through the process without yeast affecting them, and they break down very slowly later top release the staling compounds. 48:00 Bamforth's main point is that that wort is full of lots of things, lots of interactions. You can argue what you want via paper chemistry, but the acid test comes down to what is generic that you can do to slow down these reactions in the finished product. Sometimes this is just rote, basic stuff nothing fancy. 49:00 At an MBAA meeting in Milwaukee, Bamforth gave a talk where they expected great things, but what he said was this: (1) Consider using SO2; 2) Keep oxygen exposure as low as reasonably possible; (3) Keep finished beer as cold as possible. He didn't say that much about upstream. People were disappointed in this basic, conventional approach. What about all the investment in minimizing O2 uptake in the brewhouse? In Bamforth's opinion, until you have the latest technology in packaging equipment to keep O2 to absolute minimum, you are wasting your money. If you have no control over shipping and storage, then irrespective of what great things you've done in the brewhouse, the damage will be done to the beer anyway. So Bamforth wouldn't invest his next year's salary in saying HSA is critical. 51:00 The biggest factors, and overwhelmingly so, are oxygen in specifically the finished product, and the temperature you keep that product. 51:00 Svante Arrhenius, a chemist and physicist, showed that every 10 C rise will increase chemical reactions 2-3 times faster, and this rate compounds. 52:00 So consider beer at 20 C that lasts three months. If you go to 30 C, it will stale in 4-6 weeks. At 40 C, it's down to 10 to 20 days. At 60 C it can be getting near one day. Laboratories use this higher temperature effect on the rate of chemical reactions to speed up staling in their quality control tests. They use either 30 C for a month or 60 C for 1 day. On the other hand, if you cool to 10 C, the beer lasts 6 to 9 months. At 0 C, you are over a year. This is so much more dramatic than just fiddling with HSA. It does cost a lot to ship and store beer cold, but the effect is an order of magnitude greater than any upstream methods. 53:00 Summary of methods to avoid staling: Pitch healthy yeast, and then a strong fermentation will take care of most of what mistakes/oxidation were made upstream. Packaging is key. Cap on foam, and exclude oxygen. [And cold storage temperature. Not sure if he mentioned it here.] 55:00 Does Bamforth completely disregard HSA then? Well, there is no harm to do the sensible things. Rather than splash hot wort, fill from bottom. Use common sense, and reasonable means. Don't invest loads of extra money in malt varieties lacking this and that enzyme. Purging the grist with inert gas and de-aerating the water are low priority. 57:00 There is a perception that this staling affects lighter beers and lagers more than darker ales. In a robust ale, we perceive better flavor stability and more Maillard reactions. However, it's actually because these styles simply have more flavor and thus hide the deterioration better. The more complex the flavor, the better you'll mask the defects. [to be continued...] Return to table of contents
Date: Thu, 31 Dec 2009 08:54:11 -0800 (PST) From: Calvin Perilloux <calvinperilloux at yahoo.com> Subject: Oxidation and HSA by Bamforth on Brew Strong - Part 4 [continued from Part 3] 58:00 Question: What's the difference between aerating the wort before pitching, and aerating upstream (aka HSA)? With wort aeration, you are putting oxygen in there specifically for the yeast because they need it. Yeast will scavenge that oxygen straightaway to make its own unsaturated fatty acids. If the oxygen is added in too soon, then it will react with gel proteins and other things. Whether that impacts flavor is debatable, but upstream oxygen is not available later in the process for the yeast, hence why we need to add it later and not earlier, when the wort is hot. 60:00 Bass experimented with oxygenating the yeast and NOT the wort. Some people are still looking at that. Some say give lipids directly to the yeast. But some oxygen is essential for the yeast to make its membranes, and you need to give it enough to get a good fermentation. Again, the early-added oxygen problem is that it is attached to other things and unavailable to yeast. 61:00 Question: Homebrewers use plain air sometimes, filtered room air, versus oxygen cylinder. Is there a difference? Is pure oxygen going in more likely to oxidize than plain air? Bamforth is not convinced that it would have a significantly different effect, though that depends on whether you have given more than the yeast needs. Some yeast don't even need air-level oxygen saturation rates; others need full, pure-O2 saturation levels; nobody knows why this is for different strains. 63:00 In order to avoid fermentation problems, smaller brewers would generally err on side of caution and add more oxygen than is needed, but if there is too much then you will get more yeast, which is fine on a small scale, but on a big brewing scale where small differences translate into big dollars, more yeast mass means less beer/alcohol! But for small scale brewing, it is not important which aeration method is used, in his opinion. 64:00 There is a chemist in Holland who disagrees with Bamforth about LOX (lipoxygenase), so there is apparently some debate still on the issue. [Ed: I note that Anna Douma and other Dutch researchers have been heavily involved in patents for lipoxygenase-deficient barley.] 65:00 As for finished beer, oxygen can creep in between neck of the cork and the bottle; cans are actually a better bet for sealing out oxygen. Sierra Nevada has switched to a new bottle cap to reduce oxygen ingress; they've gone away from twist off caps to pry-off because there is less leakage in the standard pry-off caps. 67:00 How are aluminum cans for storage? As long as the can is properly coated internally, then in terms of flavor stability, a can is actually superior to a bottle. Of course, that depends on the product, and you also should consider the customer's perceptions. [End of notes] Corrections welcome. - -- Calvin Return to table of contents
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