Trans-2-nonenal

[Geoff Logan]

How much of a role does hot side aeration play in the formation of trans-2-nonenal or it's precursor's? I've heard conflicting arguments and would love a little sound advice. I'm working with a Peter Austin system and producing only ales right now. So regarding splashing, floating mashes, etc; what is the impact on shelf life? Thanks.

Geoff Logan
Head Brewer
AleWerks
Williamsburg, VA

[Roger Greene]

Wort Oxidation

T2N is formed from the enzymatic (LOX) and non-enzymatic (supperoxides) oxidation of UFAs to form hydroperoxides that can be degraded further into carbonyls. Temperature plays a huge role in these reactions by accelerating the rate at which they occur. Normal oxygen (in it's triplet state) is not very reactive, but with the addition of heat or transitional metal ions such as Cu or Fe, superoxides are formed. When it comes to ensuring a good shelf-life, hot side aeration should be minimized. A gentle handling of the mash and wort is the best way to achieve this. Also, it is believed that the presence of Maillard reaction products found in darker malts (cara, black, etc.) can show some inhibitory effects on the LOX enzymes. So, what does this all mean? Basically, there is very little that can be done without investing in new equipment. Just make sure to avoid any foaming of the mash, and if possible, transfer the wort into the kettle via the bottom. Luckily, with heavier flavored ales, the effects of wort oxidation are a lot harder to notice in the final product. Hope this helps some, and if you have any other questions just ask!

[Moonlight]

Perhaps a nitrogen purge of the mill would keep the floating/aerated mash from being a concern?

[Geoff Logan]

...Basically, there is very little that can be done without investing in new equipment.

That's kind of what I was afraid of. I am interested in the Nitro purge of the Mill. My setup is pretty basic: An Apollo mill through a flex auger at roughly 33 #/min. I've seen better augers/mills with purge systems and wet milling, but has anyone ever purged a simple flex auger? Is it possible, or even worth considering? I can't mash under nitro because my MT isn't sealed completely. Anyway, the tips are greatly appreciated.

Geoff

[paul farnsworth]

HSA phobia

Geoff
Congratulations. Hot-side aeration( HSA) is a topic that always produces ‘robust’ discussion amongst academic brewers! Here is my take on this, just to stir it up a little!
There are a variety of compounds that give beer a stale character.
One is trans-2-nonenal, but it's not just this you need to worry about. An entire family of compounds called Carbonyls are commonly found in stale beers (and cucumbers and human sweat!). These can come from the oxidation of fatty acids during hot wort aeration, but also from the thermal breakdown of malt and hop proteins.
The presence of oxygen during mashing may encourage carbonyl formation, but much of this is driven-off during the boil.
There are some who argue that you should actually promote mash oxidation so you can get rid of the oxidized products by boiling, so then you then have a cleaner beer, though this may be going a little to far.
An argument can also be made that oxidation in the brewhouse is irrelevant because yeast will clean up the staling compounds during fermentation. Budweiser bubble air through hot wort in order to strip out DMS and their beers rarely show oxidative staling!
Overwhelmingly the biggest factors in beer stability are minimizing oxygen levels in the finished product and the temperature at which you keep that product. Until you have the packaging equipment to keep O2 to an absolute minimum in the package, and complete control over your distribution-chain conditions, Hot Side Aeration is not critical.
Historically the origin of the ‘HSA-is-bad’ story probably lies in the packaging department having been given grief by QC because of poor product shelf life. Packaging knows that there are only parts per billion of oxygen in the bottle, so they blame the brewhouse. The brewers know they are not splashing hot wort and are even using de-aerated water and nitrogen blankets on the mash tun so they blame the maltster. The maltster breeds a new ‘low-oxygenase’ malt variety and the blame-cycle starts again! The brewing-chemists battle continues!
Bottom line.
If you are a brewpub don’t worry about HSA. If your beer is starting to stale, call it ‘aged’ and brew smaller batches. With higher gravity, well hopped beers, slight oxidation will be masked or may even be a good thing, especially if your sales are up and your beer does not have sufficient time to ‘mature’.
If you are a packaging brewery don’t worry about HSA, worry about ‘cold side aeration’. Minimize oxygen exposure during beer transfers and filtration. Keep package oxygen below 150 ppb. Keep beer cold during its entire time in the marketplace and sell only enough that it is on the shelf for less than 2 months.
If your brewery cost over $10’s of millions to build and you have state of the art packaging technology and you are shipping beer abroad, then maybe you should worry about HSA!


Dr Paul Farnsworth University of new Mexico

[Roger Greene]

If your brewery cost over $10’s of millions to build and you have state of the art packaging technology and you are shipping beer abroad, then maybe you should worry about HSA!

Exactly. Dr. Farnsworth is right on this. As a small brewer, wort oxidation would probably be the last thing to cause an issue, unless you are looking to make a light lager.

[Moonlight]

just to stir it up a little!

Well explained-thank you! And Special thanks for the desire to stir things up!

[HinduKush]

Well said Dr. Do you still sell reconditioned scopes and lab supplies?

[Geoff Logan]

Excellent. One less thing to keep me up at night...for now at least. Thanks all.

Geoff

[john wonder]

Why Nitro?

Pure Nitrogen is lighter than air so it will blow off. At my last solo brewing job I would take a hose off of a mildly fermenting batch and sparge my MT and kettle just for kicks and actually leave it in during boil. CO2 sits like a rock on the bottom. Not as well as argon but it's free. Does anyone see a potential problem with CO2 blanketing on the hot side?

I am wondering about this because we need to upgrade on size and there is an affordable 50Bbl with an internal calandria but the boss (not a brewer) doesn't like hot side aeration.

Thanks,
John