Aeration, Oxidation and HSA

[Gurgeh]

Trying to get the definitive on aeration, oxidation and HSA...

how can you tell that you have sufficiently aerated your wort?

are the effects of HSA proportionate to temperature, or are they entirely eliminated below 24C

at what stages during wort production is HSA an issue (i.e. vigorous stirring of the mash?)

if a wort is under-aerated, the wort will under-attenuate. what are the effects of over-aeration (at pitching time)

at what point during the fermentation is the introduction of oxygen going to cause maleffects?

what would be the effect of NOT aerating the wort, but having a highly aerated starter, so that the balance is equivalent to optimum aeration (i.e would it give the yeast as much oxygen as it needs without actually causing any oxidation in the wort)

Cheers!

[iowalad]

My aeration technique is the old back and forth pour.
I stop when the FV is filled with froth (well and wort underneath).
Probably not the smartest to be picking up 5 gal and pouring back and forth but it is little American gals so it isn't too bad.

As far as HSA I don't think it is much of an issue for the typical homebrewer. That being said I try to minimize splashing and such. From nonscientific tests from people on other forums (Northern Brewer for one) it appears that HSA isn't an issue for running ales as they get consumed before the ill effects are shown.
Some brewers here take no precautions against HSA and report no ill impact to their brews.

I don't think you can overaerate with air. With Oxygen I have read reports of the beer tasting thinner or smaller than it is.

I think there are brewers who only aerate their starters and leave the wort unaerated.

[Reg]

at what point during the fermentation is the introduction of oxygen going to cause maleffects?

Cheers!

Once fermentation is going, oxidation is unlikely to be a problem whilst the ferment is strong.

In my experience bottling can be an issue. I lost a couple of small batches until I isolated the fact that the rather short piece of hose I was using (I was focussing on keeping a tidy setyp at the time) was forcing me to drop rather then settle the beer into the bottle.

There are times when less is certainly not more!

[Graham]

Trying to get the definitive on aeration, oxidation and HSA...

how can you tell that you have sufficiently aerated your wort?

are the effects of HSA proportionate to temperature, or are they entirely eliminated below 24C

at what stages during wort production is HSA an issue (i.e. vigorous stirring of the mash?)

if a wort is under-aerated, the wort will under-attenuate. what are the effects of over-aeration (at pitching time)

at what point during the fermentation is the introduction of oxygen going to cause maleffects?

what would be the effect of NOT aerating the wort, but having a highly aerated starter, so that the balance is equivalent to optimum aeration (i.e would it give the yeast as much oxygen as it needs without actually causing any oxidation in the wort)

HSA is not an issue in my view. To me it is a myth that seems to have been originated by the late George Fix and propagated, argued about, and generally discussed ever since. For years it was the most highly argued subject - real hot arguments - on the American HBD, and it still crops up regularly many years later. It is a great shame that George Fix and some of the fiercest supporters of HSA (usually Americans), had not seen the working practices of a typical, traditional, British steam brewery. If they had, they would at least have had to have a re-think and modify their ideas if not abandon them altogether.

If HSA does exist, and I don't believe it does, it is a POSITIVE benefit, not a negative. I say this, not based on any scientific knowledge of the subject, but just the way the smaller (and many of the bigger) highly respected British breweries worked.

Okay, the traditional type of British brewery is fast disappearing these days, but there were, and still are, people that know absolutely nothing about brewing, or what the inside of a brewery looks like, and yet very highly value the beers from traditional old-fashioned breweries, based simply on taste. Such breweries as: Gales, Harveys, Hook Norton, Jennings, Adnams, Wadsworth, Morells, Morlands, Burton-Wood, Arkels, Brakspears, Wethereds - the list goes on.

These breweries took no precautions whatsoever to eliminate air from hot wort, - indeed, looking at the way they splashed hot wort about you would think they were positively trying to encourage oxidation.

From the mash tun, the sweet wort was splashed from the taps into the underback, which is nothing other than an open vessel, then often run in open troughs to the spendsafe or directly into the copper; splashed into the copper from way above the surface while filling. Even the act of boiling the wort is spectacular. All traditional coppers are fitted with an internal calandria; a device that behaves like a coffee percolator. The end result of this is that a fierce fountain of wort shoots, at surprising velocity, up a vertical tube in the middle of the copper, hits a mushroom-shaped spreader and then sprays down onto the surface of the wort. It looks for all the world like a pumped fountain, but it actually works by convection currents. The reason for this device is for better agitation to improve break and hop utilisation for a lower level of energy, but boiling wort coming into contact with air is inevitable. However, air can not go into solution at these temperatures, but that doesn't mean that oxidation couldn't occur if it really was an issue.

From the boiler the wort is splashed into the hop back, from there pumped to the top of the brewery into holding tanks, often the old "coolships" which are huge but shallow (4 - 6 inches deep) cooling trays in the brewery attic, exposing maximum surface area to the atmosphere. From there, the wort flows to the coolers, which these days are counterflow plate chillers, even in the most old-fashioned brewery, but I can still remember seeing the old-style "refrigerators" in use, which were external coolers whereby the hot wort trickled like a waterfall over a series of pipes through which cold water was pumped.

So, at every stage of the traditional brewing process, opportunities for oxidation occur, but that does not seem to have damaged the reputation of dozens of British breweries; on the contrary, the beers from these breweries were more highly respected than their modern brewery counterparts.

Looking at the Interweb, even those "experts" that go along with the idea of HSA differ widely on their interpretation of it, and how to avoid it. However, they generally seem to be coming round to the idea that it doesn't happen during the boil. This is a departure from the situation a few years ago, and I think, rather than any scientific thinking, it has more to do with the fact that some of them have now seen the inside of a commercial brewing copper. Almost all commercial brewing coppers have a "fountain" and "spreader", even modern ones, small ones and big ones, and even American ones, because the increase in efficiency makes such an arrangement advantageous. If HSA occurred at this point, then damn near every commercial beer in the world would be oxidised.

Some proponents say that HSA can occur during the mash, or that the mash is the most dangerous time in this respect, so if you are at all worried about it, overenthusiastic stirring of the mash should be avoided as you suggest. I still don't believe it though.

As for the other questions, I agree with all the other posts here.

You can't over-aerate with air. Indeed some yeasts require re-aeration during fermentation to maintain vigour.

An over-aerated starter won't be good enough. Indeed you won't be able to over-aerate anything. The amount of air that you can get into a wort has scientific limits that are fairly low. Indeed, as above, sometimes a saturated wort - even a full sized batch - isn't enough to maintain vigour and will require re-aeration during fermentation.

Aeration during fermentation will not be a problem because the yeast will scavenge it almost immediately.

Aeration or oxidation becomes a problem after fermentation is complete, or particularly after the beer has cleared and yeast counts are low. This is most important during bottling because it is usual, in my case at least, to clear the beer in cask first before bottling, giving very low yeast counts. A long rigid tube reaching to the bottom of the bottle is what is required, as someone else suggested.

It is probably a good idea to observe the same precautions when cask filling, although the high yeast counts present during typical cask filling are probably enough to scavenge, although it would be unwise to rely on it, particularly in view of some of the (perfectly valid) brewing methods and practices advocated on this site.

Oh dear, Rambling Syd Rumpo rambles on yet again.

[Gurgeh]

I'd call that pretty definitive - thanks

[Scooby]

And long may he ramble. That was a fascinating reply the best and most interesting on any subject that I have read

[Dan]

nice post graham

I read somewhere that the dense steam comming off the boiling wort could be enough to displace and drive away the air, thus protecting the wort against aeration.

If HSA occored anywhere in a homebrew set up i would point a finger at recirculation of the mash. a poorly sealed pump could potentialy foam up wort at 65C and could do so for a full 90 mins

[steve_flack]

My brewery has more opportunities for HSA than most - I recirculate my mash with a pump. I haven't noticed any HSA effects. If it were a problem you could add metabisulfite to the mash to reduce it (I don't).

If it does exist, I think HSA is more of a problem for very pale, lightly flavoured lagers that will sit around in bottles for a while - like Bud. For beers with flavour that get drunk in a matter of weeks it's a non-issue IMO.

[Aleman]

If it does exist, I think HSA is more of a problem for very pale, lightly flavoured lagers that will sit around in bottles for a while - like Bud.

And I think the funniest thing to know is that Bud use a protein stripper during production. Essentially two tall towers into which air is pumped a high volume from the bottom, HOT WORT from the boiler is introduced from the top, any protein matter gets trapped by the bubbles and carried to the top of the tower where it goes to waste. (A huge version of a Protein skimmer used in Marine Reef Aquaria).

Like Steve I use a RIMS during mashing and have yet to experience any examples of HSA, Looking into this a few months ago I came across a paper that measured the precursors of T2N in malts and US 6 Row malt was found to have very high levels, much higher than European 2 row malts. SO again this could be a factor. And as an old Bass brewer was heard to lament "Our Trade is Rapidly becoming a running one", In other words the beers do not hang around long enough for HSA to become an issue (If it is going to be). The real enemy of beer post production is Cold side aeration and many breweries go to extreme lengths to eliminate any possibility of 'bottled' beer coming into contact with oxygen.

I once had an accident with a plastic boiler. The boil had almost finished, I was attaching the CFC tube to the tap, when in my typical Cack handed fashion I pulled the tap out (Why is our first reaction to block the hole ? ), after a couple of attempts to re insert the tap (Bear in mind that the boiler contained 30+ litres of boiling wort) I grabbed the FV and let it all pour into the FV (a jet of wort shot out 3-4 feet long), hops break and all. After a quick trip upstairs into the cold shower for 20 minutes, I then repaired the boiler poured the wort back in and continued making the beer. (Strong Mild Based on Sarah Hughes ~ 1.070) After 11 months in a KING KEG the beer was still sound.

I've never boiled in plastic since