Aeration/Oxidizing

[brmdavis]

What is the difference? When is it good and when is it bad? I started homebrewing after watching the Good Eats episode in Jan of 06 and have done est. 20 odd batches. Each time i pour the wort into the primary from the boil (i do only extract and the occasional partial mash only recently) i try to not splash at all b/c according to good ol' alton brown, this will oxidize the wort and make it nasty. I've since read dozens of posts of people not only purposly splashing their wort, but shaking it up in carboys, putting in airstones and fish pumps, and injecting pure oxygen in the wort. I've also read threads of people saying to aerate at specific temperatures, don't do it hot- wait for it to cool. When is good and when is bad?

I was also transfering a stout from a secondary to the botteling bucket using a different method, i put away my auto siphon (that works awesome by the way) and used the racking cane- carboy-nipple-blow-to create positive pressure-transfer method that i read recently just to see if it worked. It did but i also lost the suction a couple times and restarting it caused bubbles in the botteling bucket. What affect, if any, will this have on the brew?

At what points of the brewing process does aeration have a positive/negative effect?

 

[Orfy]

Aeration while the wort is cool and before the yeast finish is good.
Whilst hot and after the yeast has finished is bad.

 

[dcbrewmeister]

You've overcomplicated a simple subject. It's easy.

The only time you want to aerate/oxygenate your wort is before pitching yeast, all other times is bad.

Think of it this way, open a beer and leave it out over nite, in the morning drink it. If you aerate your beer at any other time besides aerating to pitch, that is what you will end up with. Racking is one of the times that it has a chance of happening, 'specially when your racking cane sucks air.

 

[brmdavis]

You've overcomplicated a simple subject. It's easy.

The only time you want to aerate/oxygenate your wort is before pitching yeast, all other times is bad.

Think of it this way, open a beer and leave it out over nite, in the morning drink it. If you aerate your beer at any other time besides aerating to pitch, that is what you will end up with. Racking is one of the times that it has a chance of happening, 'specially when your racking cane sucks air.

Understood but what about the temperature factor; I've read a few contradicting posts. I guess my reason for the question is i'm doing a batch tonight. When i transfer the wort from the boil it's still piping hot, then i add ice cold water to bring to 5.5gal in an effort to cool the wort.

When i transfer the wort from the boil to the primary should I:

A) Tilt both vessles and slowly let it trickle down the side disturbing the liquid as little as possible

or:

B) Climb a ladder and dump it from 10 feet up, agitating it as much as possible.

 

[the_bird]

If it's hot, DON'T aerate. The only time you want to introduce air or O2 to the brew is immediately prior to pitching, when it is cool.

 

[brmdavis]

Racking is one of the times that it has a chance of happening, 'specially when your racking cane sucks air.

Have you ever experienced this first hand? Causing an off taste that is?

 

[brmdavis]

If it's hot, DON'T aerate. The only time you want to introduce air or O2 to the brew is immediately prior to pitching, when it is cool.

Thanks bird...I'm going to test your knowledge a little more. Why is O2 addition while hot bad?

 

[Orfy]

Why not add the water gently to the boiler? Then when you transfer to primary you can dump and splash to aerate.

 

[the_bird]

Thanks bird...I'm going to test your knowledge a little more. Why is O2 addition while hot bad?

Well, it's not a topic without controvery. Do a search on "hot side aeration" and you'll quickly see what I mean. In short, it is posited that aeration of the wort while it is still hot can cause the beer to go stale prematurely. It's something that the big brewers seem to pay a lot of attention to, although the impact on the homebrew scale is debatable. Does seem to be a lot of evidence that HSA exists, but how big of a problem it really is? Hard to say.

In any case, it's one of those better-safe-than-sorry situations, IMHO. Just be smart, don't stress if you splash around a little, but there seems to be no reason to intentionally introduce air into hot wort. Cool, THEN aertate through any of the methods discussed (splashing, running through a fine mesh strainer, pouring back and forth between vessels, or an aeration/O2 system).

 

[Chairman Cheyco]

Do a search on "hot side aeration" and you'll quickly see what I mean.

Yeah, that's a tough one. Everyone is afraid of it and nobody seems to be able to give proof from experience.

 

[the_bird]

I think it was the guys from Basic Brewing Radio who did an experiment that seemed to show SOME effect, although not terribly dramatic. Again, one of those where I personally don't see the need to be overly stressed, but at the same time to not totally dismissive.

 

[Orfy]

I think it was the guys from Basic Brewing Radio who did an experiment that seemed to show SOME effect, although not terribly dramatic. Again, one of those where I personally don't see the need to be overly stressed, but at the same time to not totally dismissive.

They basically couldnt detect oxidised beer no matter how much they abused it.
Alcohol Abuse!

Beer is real tuff stuff. As long as you follow a few simple basic rules then it will be good.
DWRHAHB!!!!!

Thanks Bird for the proof reading.

 

[the_bird]

As I recall that episode, they slightly detected some oxidation, but I can't recall how long they let the beers age. My impression has been that the issue with HSA is long-term storage, not necessarily that it'll taste like crap right away.

 

[Chairman Cheyco]

What a lovely thread this is...

 

[user 4295]

I know that I've been doing this a lot lately, but here is what John Palmer has to say on the subject. I'm glad that some of the questions around here lately have driven me back to John's book "How To Brew". I keep forgetting how much info is there.

Aeration is Good, Oxidation is Bad

The yeast is the most significant factor in determining the quality of a fermentation. Oxygen can be the most significant factor in determining the quality of the yeast. Oxygen is both your friend and your enemy. It is important to understand when which is which.

You should not aerate when the wort is hot, or even warm. Aeration of hot wort will cause the oxygen to chemically bind to various wort compounds. Over time, these compounds will break down, freeing atomic oxygen back into the beer where it can oxidize the alcohols and hop compounds producing off-flavors and aromas like wet cardboard or sherry-like flavors. The generally accepted temperature cutoff for preventing hot wort oxidation is 80°F.

Oxidation of your wort can happen in several ways. The first is by splashing or aerating the wort while it is hot. Other beginning-brewing books advocate pouring the hot wort after the boil into cold water in the fermenter to cool it and add oxygen for the yeast. Unfortunately the wort may still be hot enough to oxidize when it picks up oxygen from the splashing. Pouring it down the side of the bucket to minimize splashing doesn't really help either since this increases the surface area of the wort exposed to the air. Thus it is important to cool the wort rapidly to below 80°F to prevent oxidation, and then aerate it to provide the dissolved oxygen that the yeast need. Cooling rapidly between 90 and 140°F is important because this temperature region is ideal for bacterial growth to establish itself in the wort.

In addition, if oxygen is introduced after primary fermentation has started, it may cause the yeast to produce more of the early fermentation byproducts, like diacetyl. However, some strains of yeast respond very well to "open" fermentations (where the fermenter is open to the air) without producing off-flavors. But even for those yeast strains, aeration or even exposure to oxygen after fermentation is complete can lead to staling of the beer. During racking to a secondary fermenter or to the bottling bucket, it is very important to prevent gurgling or splashing. Keep the siphon flowing smoothly by placing the outlet of the siphon hose below the surface of the rising beer. Decrease the difference in height between the two containers when you begin. This will slow the siphon rate at first and prevent turbulence and aeration until the outlet is beneath the surface.

To summarize, you want to pitch a sufficient amount of healthy yeast, preferably grown in a starter that matches your intended fermentation conditions. You want to cool the wort to fermentation temperature and then aerate the wort to provide the oxygen that the yeast need to grow and reproduce. Then you want to protect the beer from oxygen once the fermentation is complete to prevent oxidation and staling.

John

 

[the_bird]

Nobody seems to be pissed off, so maybe this thread can be a candidate for the new, improved FAQ.

 

[Brew chick]

from everything that i,ve ever read the reason we airate wort when cool is becouse oxygen dissolves better into solution than when the wort is hot.

 

[Orfy]

again.

Hi Brew Chick. I was by Barnsey (Oxspring) on Sunday for the Sheep Dog trials.
And, I have a pint of Old Speckled Hen in my hand now.

 

[Brew chick]

nice one ORFY,enjoy!

 

[Biermann]

I think what it boils down to is the simple difference between oxidation and oxygenation.

Oxidation is a process that is catalyzed by heat to form a covalent bond between oxygen and organic compounds present in the beer. These compounds, although not initially detectable in the beer, may be degraded by yeast and age to form various esters and aldehydes that cause off flavor in beer. Hence, splashing hot liquid will further oxidation as it is a heat-catalyzed process. Covalent bonding may be considered permanent when talking about beer.

Oxygenation is the process of dissolving O2 molecules in water through ionic bonding. Since yeast initially undergo an aerobic form of metabolism to replicate and increase their numbers and metabolism, O2 dissolved in solution is vital to early yeast activity--Its the yeast's capability to undergo anaerobic metabolism (once the O2 has been eaten up, and the replication phase has ended) that causes them to produce EtOH (ethanol) and Carbon Dioxide. Initially, yeast produce mostly water and CO2 aerobically--once the oxygen is gone, they undergo anaerobic metabolism, and breakdown lactate/pyruvate to Ethanol and carbon dioxide.

Once the yeast have no more usable/fermentable sugars (at the end of fermentation), oxygenation may slowly cause oxidation--If you heat finished beer and splash it around, you'd get oxidation much faster.

So: don't splash or aerate hot--

and don't splash or aerate once the beer is finished.

Aerating cool wort to provide essential nutrients for yeast, however, is essential--it will allow appropriate numbers of yeast to produce a vigorous, highly attenuative fermentation.

Cheers!