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	FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
		Digest Janitor: pbabcock at hbd.org


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Contents:
  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



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