Hot Side Aeration

[Rosie]

Hi Guys,

I've been brewing on a new plant that has some hot side aeration (HSA)
issues in the process...specifically, splashing in the underback/grant and
the kettle.

What should I be looking for in my packaged product (keg now, bottles
shortly) as a result of this HSA? Currently the kegs are kept cold and
consumed within 3-5 weeks and I'm not picking up any flaws from it. Mash is
single infusion at 65C.

Am I right to be worrying about it? Or, is this a case of HSA really not being
a problem?

I think I'll just fix the problems and stop worrying...but any advice and experience appreciated.

Cheers,

[dick murton]

Where are you aerating ? It sounds like you are aerating in the kettle. You can only realistically aerate just prior to the wort cooler, so the oxygen does not stay in contact with the wort to appreciably oxidide the wort, but is immediately cooled so the oxygen stays in solution If you are trying to oxygenate / aerate in kettle, then virtually all will immediately flash off. You will have virtually none remaining in solution when the yeast hits the wort.

Hot side aeration with ales is not normally too much of a problem, especialy if using air rather than pure oxygen. It is the lager brewers who voice concerns over colour pickup in particular, and because so many are low flavour products - some oxidation can be picked up - but often not in final package if the beer gets oxidised due to poor O2 control or overpasteurisation

Cheers

[Rosie]

Thanks for the reply Dick!

Sorry, to be clear, we're not aerating in the kettle and the underback on purpose...it's just the design of the system. I was just wondering if it was worth worrying about or not as you often hear of people fearing hot side aeration.

We aerate again on the way to the fermenter (cold side) with regular old air, and have decent results...

Cheers,

[gitchegumee]

There are those who don't think HSA is much of a problem (outside of color increase). They argue that the wort is too hot to dissolve oxygen and that any oxygen that does dissolve will be flashed off just as quickly. Hot aqueous solutions tend not to dissolve gases as well as cool liquids, it's true. I believe that HSA is a problem based not on dissolved oxygen, but on the much quicker reaction rates at high temperatures. Any oxygen entering the wort would likely react very quickly to promote staling reactions before it flashes off. Hot aqueous solutions tend to be more reactive than cold ones. Much more so. And the reaction doesn't need oxygen to dissolve--it can still occur as a surface phenomenon. Splashing increases the surface area. These staling reactions include trans-2-nonenal, which tastes like wet paper/cardboard and often takes time to develop. I've found that they can limit shelf life substantially. That being said, if you store the beer cold, and serve it all before 5 weeks, then maybe your concern hasn't had time to manifest itself. Why bother, right? Let sleeping dogs lie. But then again, for the minimal effort it would take to decrease the HSA problems you've outlined, you could gain some minimal increase in quality. Up to you! Cheers!

[crassbrauer]

Whether or not your beer is fresh, there can be evidence of hot side aeration in the flavor, especially in lighter beers. A harshness in the aftertaste is not uncommon, instead of pleasant bitterness from the hops. Then there's the aforementioned cardboard, etc. later, as well. Even those fruitier, darker beers will benefit from lack of hot side aeration.

As Gitchegumee and many others have pointed out time and again on this forum: there is a big difference between oxidation and oxygen going into solution.

The heat during mashing, sparging, boiling and in the whirlpool provides the energy of activation for many reactions including oxidation. These are chemical reactions, which change the molecules from good to bad things for your finished beer (for the most part, although melanoidins are made, as well). When the wort is cool the energy of activation is low and therefore not as much oxidation occurs, although some still does. This is one reason that aerating is better than oxygenating.

When oxygen goes into solution in the beer, like salt does in water, it is still itself, i.e. no chemical change has taken place - this is merely a physical occurrence. The solubility of oxygen goes up as the temperature drops.

These are the two main reasons to get the wort down to a low temperature during cooling.

[dick murton]

Actually I think you'll find that you kill the yeast if you leave it hot. But seriously.... I wouldn't worry too much about hot aeration if you are brewing darker ales, and really you probably won't really notice much with lighter ales or lager styles. I would be more concerned about the ability to sterile filter the air / oxygen consistently. Hot side aeration has a distinct advantage there, and unless you spnd a fortune with Pall / DomnickHunter et al, then you are probably better off going for hot side aeration

Cheers