Previous Oxidation or Sulfite Research

[Owenbräu]

Use this thread to catalog old forum threads, articles, chapters, blogs, etc. where someone tried sulfites in the mash, boil or packaging. This will give us quick references for any future cations needed.

From Dr. George Fix in HBD # 1047
"Negative effects due to HSA are usually reflected in a flavor the
Germans call "Herbstoffe." Roughly translated this means "grain bitter"
or "grain astringency."
There are some theoretical considerations which suggest HSA should
be a nonissue. Ironically, the same issues arise in a project I am
currently working on which involve beers very far removed in character
from Lambics. Herbstoffe arises from the presence of what could be
called HSA aldehydes. These in turn arise from the interaction of
ethanol in beer (as well as some other things) and products which were
oxidized on the hot side of wort production. The HSA aldehydes have
been isolated, and definitely display "grain astringent" flavors.
Moreover, it has also been shown that most Saccharomyces will ignore
them. Thus, in most beers, if present, they will spill over into the
finished beer and display Herbstoffe."

[Owenbräu]

From Steve Anderson in HBD #5093:

HSA is a term that includes oxygen uptake in the mash & boil both. This
is in contract to cool-side aeration after the chill. Some studies in the
late 1968 and up to recent years attempt to trace out the fate of oxygen
in wort & beer and make decisions about there relative "badness" based on
their chemical fates. Anyway the early papers (and many since) indicate
that HSA oxygen has negative impact on flavor and flavor stability.
Chas Bamforth published a terrific paper in JIB about 5 years ago
calculating the enzymatic and catalytic pathways for various oxygen
species in the mash, then correlated his estimate with published studies
of the total O2 uptake in the mash.

Despite the fact the oxygen is not very soluble at mash temps and above -
many times the saturation level of oxygen is chemically compounded with
the mash during the mash. Nearly all of this oxygen transpires through
the air-mash boundary. Bamforth calculates that the catalytic processes
in the mash are sufficient to use up saturation levels of oxygen in a
matter of seconds !! So the mash is almost devoid of oxygen and
Henry's Law of partial pressures forces atmospheric O2 into the mash.
Bamforth doesn't directly address the issue of O2 uptake in the boil,
but if we assume the enzymatic mechanisms are lost and the metal ion
catalytic mechanisms (which are the stronger ones) are enhanced by
temperture, then the boil is probably at least as bad in terms of
oxidized products as the mash.

All this oxygen ends up compounded with wort constituents. Oxidized
oils are probably primarily produced in the mash by the action various
lipo-oxygenase enzymes. These damaged oils break down producing the
trans-2-nonenal cardboard aroma and other aldehydic aromas.
Quantitatively phenolic compounds are the greatest destination for this
oxygen in wort. Simeple phenolic compounds often have pleasant fresh
flavors - or at least innocuous ones. Oxidized phenolics are more
bitter and will polymerize and eventually produce astringency. They
also are removed to some extent in the break material and in the
"dregs" left behind in the lagering process. Fining materials like
PVPP will remove oxidized phenolics too. Many other materials in
wort are oxidized in the mash & boil too.

After the chill, a fermentation is created and the yeast during their
anaerobic ferment have a dilemma - they are required to chemically
reduce the material in their environment to achieve a redox balance.
The major destination of all this reduction is in the creation of
ethanol from acetaldehyde, but also the conversion of other aldehydes
into alcohols and some other very flavor positive effects. Yeast
also leave a little (2-15ppm) of sulfite behind in the beer and
sulfite is an antioxidant. My hunch is that lager yeasts are
the better sulfite producers, and most ale yeasts - not so much.
More recently Morton Meilgard(sp?) has noted that some of the
extreme oxygen elimination methods developed for commercial brewing
have not proven to create a measurable improvement in flavor IN
COMMERCIAL BREWING.

Note that the amount of O2 exposure is largely related to the surface
area:volume ratio of the mash tun & copper. Also the amount of
"splashing" and transfer activity must impact this significantly.
Small HB tuns will therefore have a lot more potential for HSA,
than deeper commercial tuns. Oxidation is clearly more problematic
the smaller (shallower actually) the mash.

So here are the practical points -
Preboiling your mash water will NOT have a significant advantage.
Most of the HSA oxygen is introduces through the surface (which
increases with stirrig & splashing).
I've idly suggested in the past that we could mash (&boil) under an
inert gas layer - and this really is possible. I haven't tried it.
We could introduce an oxygen impermeable barrier to reduce the surface
area of the mash & boil. Aluminum foil or a food grade plastic layer.
80% coverage would bring HB mash tuns into the same surface:vol
ratios as commerial tuns. OTOH stirring & transfer are still
problematic.

Add sodium or potassium metabisulfite as anti-oxidants to the mash.
This method has been used in many tests and has been recommended by
some of the German brewing researchers. I add 1/2 crushed campden
tab per gallon of finished beer to the mash. I've done this with
some regularity in recent years and the resulting beer is a little
fresher, and metabisulphite has a notable impact in reducing the
color of light colored beers (another impact of oxidation).
I also think M.Meilgard has a point. Well made fresh HB seldom
has an oxidation flavor problem when young, probably due to the
terrific impact of the yeast. Bottle conditioned HB also seems to
have terrific shelf life if not mishandled. OTOH kegged or force
carbonated HB sometimes doesn't last so long. Certain beers
have notable aging problems - some of the dark malts in a munich
of n-bock seem to sometimes go south in a hurry.
Do try an HSA reduction method and evaluate it for yourself. I
think the metabisulfite addition makes a clear enough difference,
but it takes a little judgement to decide when it is called for.
-S (Steve Anderson)

[Owenbräu]

Date: Sun, 25 Mar 2012 18:29:56 -0400
From: "\\-s at roadrunner.com" <"\\-s"@roadrunner.com>
Subject: Re: Oxidation Help

James R. Gregory asks for help regarding oxidation...

> I am a relatively new all grain home brewer and am trying to get rid of a
> slight "homebrew" taste in some of my brews. I suspect it may be oxidation
> related. To date I have bottle condition all brews.
>
>
>
> I am looking for advice on preventing oxidation. I try to keep splashing,
> etc. to a minimum when transferring from carboy to bottling bucket. So I am
> looking for other tips and any comments on the following:
>
>
>
> 1. Should I flush carboys, bottling bucket and bottles with co2. I
> read the recent "flushing" discussion and am still confused. Stupid
> question, but, if this is a good idea what is best way to get co2 equipment
> and rough cost.

You don't need to flush your primary fermenter as you want the yeast to
have access to O2. If you move the beer to a secondary fermenter you
should always do so while there is active fermentation under way - and
again there is no need to flush so long as the container is reasonable
full (95% full not 50%) and don't splash. If you are bottle
conditioning then I wouldn't use O2 scavenging caps, and you can just
fill normally and leave a cap sitting on top of the bottle to rest for a
minute before sealing. The CO2 from the beer will push out most of the
O2, and the remainder can be used by the yeast.

> 2. Are the more expensive bottling caps that absorb oxygen worth the
> money.
If you are bottling w/o bottle conditioning and you intend to store the
beer for much time or at suboptimal temps - then yes.


> 3. I have heard that adding a very small amount of sodium or potassium
> bisulfite to brew prevents oxidation. Anything to this and, if so, how is
> it done.
Yes - it's very effective. I suggest you start with campden tablets
(commonly used for wine making
http://en.wikipedia.org/wiki/Campden_tablets), or alternatively you can
get potassium metabisulfite powder which may be slightly better. I'd
add a minimum of 2 campden tables (~1gm) crushed to a 5 gallon mash.
You can certainly triple that amount. With "too much" you'll eventually
get a sulfury edge to the beer - not unlike a white wine - tho it
'works' well with some lagers.

Generally this makes the beer taste much fresher and a little crisper.
The sulfite acts as an anti-oxidant and even can convert come already
oxidized flavor actors to unoxidized states. The end products are
sulfate (which you may be adding as gypsum) and a little sodium or
potassium.

> 4. Any other suggestions.

In my experience it's rare to get bottle oxidation in a bottle
conditioned beer. I've done side-by-sides and the bottle conditioned
beers really do taste better much longer (it's just such a PITA to
bottle). So IF your problem is really oxidation - it's either happening
in the mash or else your ingredients are oxidized. Metabite in the mash
will cure any mash oxidation problem and maybe even help any ingredient
issues a little. My main ingredient concern would be to use good hops.
Hops oxidation is a real potential problem.

Another possibility is that you are getting yeast autolysis in the
bottle. Some yeast disintegrate after bottle conditioning and leave a
meaty-brothy flavor and even leaves some oily rancid flavors (a hint of
dead mouse). Most of the hi-alcohol ale yeasts do very well in the
bottle. Also you should end up with a little opaque layer of yeast in
the bottom of bottle - not a quarter inch.

-S

[Owenbräu]

Date: Sat, 24 Mar 2012 08:40:00 -0400
From: "David Houseman" <david.houseman at verizon.net>
Subject: Re: Homebrew Taste
Mike,
I agree that oxidation, from old stale liquid malt extract and hot-side
aeration is one of the problems with some homebrew. However in my
experience this doesn't result in the "wet cardboard" form of oxidation
which is more typically from oxygen introduced post fermentation. Rather
the result I sense is a dullness with muted, caramel-like notes. Oxidation
can take a number of sensory forms, and each person may describe their
perception differently so we may agree that oxidation isn't good and we
don't like the results.
David Houseman

[Owenbräu]

From Steve Anderson in HBD #5093:
HSA is a term that includes oxygen uptake in the mash & boil both. This
is in contract to cool-side aeration after the chill. Some studies in the
late 1968 and up to recent years attempt to trace out the fate of oxygen
in wort & beer and make decisions about there relative "badness" based on
their chemical fates. Anyway the early papers (and many since) indicate
that HSA oxygen has negative impact on flavor and flavor stability.

Chas Bamforth published a terrific paper in JIB about 5 years ago
calculating the enzymatic and catalytic pathways for various oxygen
species in the mash, then correlated his estimate with published studies
of the total O2 uptake in the mash.

Despite the fact the oxygen is not very soluble at mash temps and above -
many times the saturation level of oxygen is chemically compounded with
the mash during the mash. Nearly all of this oxygen transpires through
the air-mash boundary. Bamforth calculates that the catalytic processes
in the mash are sufficient to use up saturation levels of oxygen in a
matter of seconds !! So the mash is almost devoid of oxygen and
Henry's Law of partial pressures forces atmospheric O2 into the mash.

Bamforth doesn't directly address the issue of O2 uptake in the boil,
but if we assume the enzymatic mechanisms are lost and the metal ion
catalytic mechanisms (which are the stronger ones) are enhanced by
temperture, then the boil is probably at least as bad in terms of
oxidized products as the mash.

All this oxygen ends up compounded with wort constituents. Oxidized
oils are probably primarily produced in the mash by the action various
lipo-oxygenase enzymes. These damaged oils break down producing the
trans-2-nonenal cardboard aroma and other aldehydic aromas.
Quantitatively phenolic compounds are the greatest destination for this
oxygen in wort. Simeple phenolic compounds often have pleasant fresh
flavors - or at least innocuous ones. Oxidized phenolics are more
bitter and will polymerize and eventually produce astringency. They
also are removed to some extent in the break material and in the
"dregs" left behind in the lagering process. Fining materials like
PVPP will remove oxidized phenolics too. Many other materials in
wort are oxidized in the mash & boil too.

After the chill, a fermentation is created and the yeast during their
anaerobic ferment have a dilemma - they are required to chemically
reduce the material in their environment to achieve a redox balance.
The major destination of all this reduction is in the creation of
ethanol from acetaldehyde, but also the conversion of other aldehydes
into alcohols and some other very flavor positive effects. Yeast
also leave a little (2-15ppm) of sulfite behind in the beer and
sulfite is an antioxidant. My hunch is that lager yeasts are
the better sulfite producers, and most ale yeasts - not so much.

More recently Morton Meilgard(sp?) has noted that some of the
extreme oxygen elimination methods developed for commercial brewing
have not proven to create a measurable improvement in flavor IN
COMMERCIAL BREWING.

Note that the amount of O2 exposure is largely related to the surface
area:volume ratio of the mash tun & copper. Also the amount of
"splashing" and transfer activity must impact this significantly.
Small HB tuns will therefore have a lot more potential for HSA,
than deeper commercial tuns. Oxidation is clearly more problematic
the smaller (shallower actually) the mash.

[Owenbräu]

From Dr. George Fix in HBD # 1047
"Negative effects due to HSA are usually reflected in a flavor the
Germans call "Herbstoffe." Roughly translated this means "grain bitter"
or "grain astringency."

There are some theoretical considerations which suggest HSA should
be a nonissue. Ironically, the same issues arise in a project I am
currently working on which involve beers very far removed in character
from Lambics. Herbstoffe arises from the presence of what could be
called HSA aldehydes. These in turn arise from the interaction of
ethanol in beer (as well as some other things) and products which were
oxidized on the hot side of wort production. The HSA aldehydes have
been isolated, and definitely display "grain astringent" flavors.
Moreover, it has also been shown that most Saccharomyces will ignore
them. Thus, in most beers, if present, they will spill over into the
finished beer and display Herbstoffe."

[Owenbräu]

Below is from an article in BYO entitled Fermentation & Flavor Compounds: Homebrew Science December 2002.

The flavor that I am trying to understand in a German Lager is not rotten egg (H2S) or struck match flavor (SO2). It is also not “cooked corn to cooked vegetables, cabbage, onion, even garlic”. As I posted previously I used the words “buttery sweetness” but I am uncomfortable with that description; I am very sensitive to diacetyl (which is typically described as buttery or butterscotch). The flavor that I am perceiving in some German Lagers is not diacetyl (I think).

I am not very good at putting flavors into words so I am really hoping to not have to express them. I would prefer that somebody would just say to me something like: DMS in Pilsners at non-excessive levels provides an xyz flavor which encourages a roundness and fullness to the beer (or something like that).

“Sulfur compounds:

Sulfur compounds are responsible for some of the most dramatic beer flavors. Some of the most aromatic aroma compounds have minute flavor thresholds and so, even though they are present in small quantities, can dramatically affect a beer’s flavor.

Sulfur compounds have their origins in the ingredients we use. Sulfate, sulfite and sulfide ions in the water, and sulfur compounds present in malt and hops, can all lead to sulfur flavors in the beer. Some, such as the frequently encountered DMS, have their origins in the malthouse or the brewery. Others, such as the skunky 3-methyl-2-butene-thiol, are formed from the reaction between light and hop compounds in the package.

Of the compounds actually formed during fermentation there are two main compounds of interest. Hydrogen sulfide (H2S) is the aroma of rotten eggs. Its flavor threshold is only around 4–10 parts per billion but it may be found in beer at levels of 200 parts per billion. At low concentrations, it rounds out the flavor of pale lager beers but at higher concentrations is definitely an off flavor. Some yeast strains are prone to producing more H2S than others, and lager brewers in Europe may base their choice of yeast strain on the amount of sulfur it produces. Growing yeast cells require sulfur for amino acid production, protein structure, and CoEnzymeA formation. Sulfate ions in wort are actively taken up by yeast and biochemically reduced to hydrogen sulfide. Once the need for those certain sulfur containing amino acids is met, the excess H2S is excreted from the cell. If the wort is lacking any nutrient, that may affect yeast growth then sulfur may be produced in excess.

Luckily, H2S is very volatile and is removed with evolving carbon dioxide during fermentation. Capping a fermentation vessel too early can trap H2S in beer, and higher fermentation temperatures can increase the levels. Some commercial brewers experience problems when they increase batch size as they expand production. Taller tanks can cause a pressure differential at the tank base and increase sulfur production. Wort spoiling micro-organisms can also produce copious amounts of H2S.

Sulfur dioxide (SO2) is the drying, struck match flavor and aroma sometimes found in beer. It is rare that it should be detectable in American beers although it is more common in English beers. In the UK, commercial brewers add it to beers as a preservative. It is able to mop up excess oxygen in solution and that is the primary mechanism, but it can also react with, and bind to, compounds that may eventually create stale flavors.

Sulfur dioxide can combine with aldehydes in wort to form compounds that survive processing. This prevents the aldehyde oxidizing further to stale flavors. However, if this comes into contact with air during storage it can oxidize back to sulfate and the aldehyde, which in turn reacts with a higher alcohol to produce trans-2-nonenal, the compound responsible for the cardboard taste in stale beer.

Sulfur dioxide can also be liberated from yeast cells when the growth cycle goes awry. It can be added to beer inadvertently along with isinglass finings when these finings are used as a preservative.

Dimethyl sulfide (DMS) is a troublesome flavor in beer. It can vary in intensity from cooked corn to cooked vegetables, cabbage, onion, even garlic. In Pilsner lagers, it adds a fullness and roundness to the flavor, and some pale American pilsners benefit from a fresh corn-like aroma. It has its origins in malt and is removed from beer by aggressive and volatile wort boiling.”

Cheers!.

[Bryan R]

Preventing in the home brew environment:

Mashing
The grain in the mash should be underlet or infused with hot water from the bottom up. By infusing in this manner, stirring of the grains to insure uniform mixing of the grain and hot water is not necessary. By not stirring the water into the mash, hot oxygen reactions can be reduced. (Millspaw, 1992)

BYO recommends the following technique. Add 3L of water to the mash tun, then carefully add 1kg of malt and gently mix malt into water. Continue this process until all of the malt and water has been added. This process will take longer so be sure to adjust for temperature losses

Palmer (2006) recommends adding water a gallon at a time (to all of the malt) and gently mixing the water in without aerating. He states that HSA is promoted by lipoxygenase at this stage, although as Fix sates the levels required by this reaction are very low.

Millspaw (1992) recommends adding specialty malts only in the mash out. The melanoidins formed at 77°C/170°F are more stable than those formed at the lower temperatures of conventional mashing. By adding these specialty malts only in the mash out, the brewer can make his mash more efficient by optimizing saccarification, maximizing the formation of melanoidins. This will lead to smoother and rounder flavours from the specialty grains, as well as more stable and clearer beers (Millspaw, 1992).

Mash recycling tends to remove a lot of large particulate matter that would otherwise be present in the boil. Millspaw (1992) feels that these techniques are a source of HSA and that the particulates (husks and grits mostly) provide a place for proteins to clump onto during the boil and then settle out more effectively in cooling.

However, Fix emphasises that one of the most important points it achieving reasonable wort clarity in lautering (Fix, 1999).
Transferring to the boiler

In practice if the power is switched on immediately the heating element is covered any uptake of oxygen is immediately driven off by the action of the boil (Alexander, 2009). Personally, I now collect using a tube into a 5 gallon bucket and then siphon from my collection vessel into the boiler.

Post Boil
Older books used to advocate pouring the boiling hot wort from one bucket to another to add oxygen and cool it. Unfortunately, the wort is still hot enough to oxidise and not aerate. Pouring down the side of the bucket to minimise splashing doesn’t help either since this increases the surface area of the wort exposed to the air (Palmer, 2006). Ensure the wort is below 27C before aerating air (Palmer, 2006)

Storage
In fresh beers both T-2-N and its precursors are bound up with natural sulphur compounds from yeast metabolism. However, after a lag, which is reduced if thermal or mechanical abuse occurs, the effects of T-2-N become discernible. Millspaw (1992) and Bamforth (2009) also emphasise the importance of storage temperatures. The Arrhenius equation shows that for every 10C rise in temperature a chemical reaction will perform 2-3x faster. For example if you store a beer at 20C a beer may stale in three months. A stored beer at 30C will stale in one month.

Additives
Additives could be one solution, however, the effective additives tend to have unacceptable side effects and the neutral ones rarely seem to work (Fix, 1999). The most likely additive to be of any use in the home brew environment is Potassium Metabisulphate (Campden Tablets) added to the mash (Fix, 1999, Spencer, 2006) which binds to carbonyl compounds. These haven’t gained favour in the commercial world because above certain 10ppm levels they must be stated on packaging and we “can let the wine have that dirty labelling” (Bamforth, 2009). It may therefore be an option to us, the bisulphates will bind to the staling aldeydes and masks their presence. However, these bonds are rather short lived in beer, and when they are broken, the staling aldehydes fully reveal their presence (Fix, 1999)

Summary
The effects of oxygen pick-up after fermentation are more apparent and severe than the effects of hot-side aeration. If you are thinking about changing your brewing procedure to avoid oxidation, you should begin addressing oxygen pick-up from the end of the process and work your way forward toward mashing (BYO). It is a complex interplay of reactions, including unsaturated fatty acids, melanoidins and iso-alpha-acids. It is therefore too simplistic to focus on just T-2-N as the sole cause of staling in beer (Bamforth, 1999).


References
Alexander, J (2002). Hot Side Aeration (HSA). Brewers Contact. 9, 2-5. Also published at http://www.craftbrewing.org.uk/bc/backissues.html
BYO. http://www.byo.com/stories/techniques/a ... -mr-wizard
Bamforth, C. (2009). Hot Side Aeration. The Brewing Network http://www.thebrewingnetwork.com/shows/475. Start at 13 minutes
Fix, G. (1999). Principles of Brewing Science, Second Edition. Brewers Publication (sorry not on the internet)
Garrod, P. (2008). Hot Side Aeration. Brewers Contact. 8, 4-5 Also published at http://www.craftbrewing.org.uk/bc/backissues.html
Spencer, J. (2006) Hot Side Aeration Exeriment 02/11/06. Basic Brewing radio. http://www.basicbrewing.com/index.php?page=60
Millspaw (1992). Hot Side Aeration and Beer Stability. Zymurgy. 15. Also published at http://oz.craftbrewer.org/Library/Metho ... mash.shtml

[Owenbräu]

https://www.homebrewersassociation.org/ ... ic=11392.0

[Owenbräu]

Jeff, Martin and Denny. Also, sulfites do not boil off.

https://www.homebrewersassociation.org/ ... ic=11392.0