Whys is oxygen important in brewing?

[TLServices]

Why is oxygen important?

Oxygen has both positives and negatives when it comes to brewing and beer…

Positives – it’s needed for yeast growth during fermentation. The right amount will help strong, healthy yeast cells to form and that means good fermentation and consistent beer with no ‘off’ tastes.

If you’re wanting to bottle-condition your finished beer or do likewise in any other sort of container, then a small amount of oxygen will help the secondary fermentation in pretty much the same way.

Negatives – At any time after fermentation, high levels of oxygen are likely to cause problems. Generally that can be for taste or appearance. Oxidised beer if often described as tasting ‘cardboardy’ and oxygen can increase the likelihood of haze formation when the beer’s being stored.

What sorts of levels are good?

Typically around 10-12mg/l (ppm – parts per million) is ideal for fermentation. Many big UK brewers tend to over oxygenate, up to 20mg/l to speed up yeast growth and make the fermentation stage that bit faster, but this isn’t really necessary.

These days major brewers and packaging companies are looking to keep oxygen levels down below 10-20ug/l (ppb – parts per billion). The ‘delicate’ taste of many keg/can lagers means the slightest oxidation will show as a taste defect.

Higher levels can be tolerated by more ‘robust’ beers, but it’s always good to try and keep things as low as possible!

Where is important and why?

As we’ve said, the first important place to know how much oxygen you have is when you’re adding yeast to wort. Yeast needs oxygen to grow and multiply, just as it needs the sugars from your malt. Too little oxygen and yeast growth will be poor, meaning slow fermentation; too much and the opposite can happen, your fermentation goes too fast. Both situations end with beer that doesn’t taste like you wanted.

If your brewing equipment allows, you can control the amount of oxygen you have in your fermenter by aerating the wort. This needs sterile air, a pressure regulator, some pressure tubing and a fine jet or sinter to make tiny bubbles (these dissolve better).

On a smaller scale, stirring or shaking will work almost as well.

After fermentation is complete, all the oxygen should have been used, so making sure it stays low will help keep that beer in good shape!

- If you transfer from fermenter to maturation, you want to be sure any pipes, pumps or other equipment aren’t allowing oxygen in;
- If you filter into bright tank, again keeping dissolved oxygen levels as low as possible helps your beer to maintain condition and taste;
- In package – cask, keg, bottle or can – careful handling ensures your beer reaches the consumer bright, clear and tasting fresh.

At any of these post-fermentation stages, high oxygen levels cause two major problems – taste defects and haze:

- Typical taste problems caused by high dissolved oxygen levels are stale, ‘paper/cardboard’ flavours on finished beer.
- Age-related haze and chill-haze are both adversely affected by oxygen, which increases the formation of visible haze compounds.

Cheers! :

 

[ano]

The ‘delicate’ taste of many keg/can lagers

:rofl:

Good post.

In my experience I've noted my beers as they get older produce something which tastes a bit like, for want of a better word, sherry. Could this be oxygen related? Or am I on the wrong track?

 

[jamesb]

In my experience I've noted my beers as they get older produce something which tastes a bit like, for want of a better word, sherry. Could this be oxygen related? Or am I on the wrong track?

Isn't sherry just a strong oxidised wine?

So that would make sense.

I've never tasted it myself though, my beers don't last that long.

 

[Aleman]

Ano, Sherry (or Acetaldehyde) is the classic sign of post fermentation oxidation . . . The stale cardboard aroma/taste is a lot less frequent and is generally only found in 'delicate' lagers that have been stored for a long period of time (like 6 months plus) . . . and even them may not manifest itself depending on the malt used and the maltsters skill.

Generally I would say that you have a couple of things to do that would help sort your problem out.

1) Drink your beer faster :lol:

2) Pay closer attention to the amount of splashing that occurs when transferring fermented beer. Syphon tube to the bottom of casks, flush receiving casks with CO2. . . . Transfer some yeast (Live Yeast is a great antioxidant )

 

[TLServices]

My associate 'taste trainer' - veteran of many a brewery session! - tells me acetaldehyde is 'green apples' rather than sherry...but yes, that sherry taint is often a result of poor post-fermentation management and high oxygen levels.

Acetaldehyde formation happens during/after fermentation where the yeast is skimmed too early as the yeast will convert it to ethanol if left. Also, conversely, it can re-form in secondary fermentation, especially where the beer is infected.

 

[ano]

Well it was in a

In my experience I've noted my beers as they get older produce something which tastes a bit like, for want of a better word, sherry. Could this be oxygen related? Or am I on the wrong track?

Isn't sherry just a strong oxidised wine?

More properly it's fortified wine, so it's a white wine with brandy added, then stuck in a barrel to age. But yes it may well have oxidised so being the flavour i'm thinking of.

My "oxygen management" isn't atrocious post fermentation. I rack to a bottling bucket using a syphon to the bottom. Then a bottling stick to the bottom of the bottles which produces very little visible "froth", and I always have plenty of yeast transferred judging by the resulting sediment :lol: But there's no doubt room for improvement.

I only noticed it in bottles of around 9 months old (which I found in the bottom of a cupboard I'd forgotten about). They'd also been stored a touch on the warm side which may not have helped.

edit: given that oxygen is used in yeast reproduction it may be that the sediment is actually evidence of poor oxygen management :hmm: Food for thought at least.

 

[Aleman]

In my experience I've noted my beers as they get older produce something which tastes a bit like, for want of a better word, sherry. Could this be oxygen related? Or am I on the wrong track?

Isn't sherry just a strong oxidised wine?

More properly it's fortified wine, so it's a white wine with brandy added, then stuck in a barrel to age.

Actually its only the really nasty stuff (Amontillado and Oloroso) that is fortified and sweetened . . . .Then shipped to us Brits :sick: . . . . . . The really good stuff is fino or even manzanilla, which is a delightful crisp dry white wine. . . . . once fermentation is over then brandy is added (to about 15% in the finest young wines) and put aside to age whereit is exposed to oxygen which encourages the yeast to develop a 'flor' at the surface preventing an excess of oxygenation while it ages. . .

 

If your brewing equipment allows, you can control the amount of oxygen you have in your fermenter by aerating the wort. This needs sterile air, a pressure regulator, some pressure tubing and a fine jet or sinter to make tiny bubbles (these dissolve better).

Ignoring the "sterile" bit and assuming "particle" free air through an aquarium "air stone", how long should I aerate for at the pitching of the yeast (or before)?

 

[TLServices]

Aeration needs to be done immediately before pitching. Aerate when you have pitched and you risk localised high levels damaging the yeast.

Aim to 'stir' the air supply through the wort for about 30 seconds. Again this is dependent on brew size and, unless you have a DO2 meter - which may or may not be cost-effective depending on your brew - it's a matter of trial, but better to be on the low side to begin with.

On the subject of meters, I have been asked in the past if the small hand-held units - usually designed for testing water or aquaria - are useable for beer. The answer is that they are generally designed for much higher levels so don't give the accuracy especially for finished beers.

 

[laighleas]

Umm! I know it is an old thread but there's an inaccuracy or two.

The yeasts in a sherry flor are 95% S cerevisiae subspecies. Of that 95%, 75% is S. cerevisiae beticus followed by montuliensis (15%), cheresiensis (5%), and rouxii (1%).

http://www.mendeley.com/research/evolut ... erry-wine/

You probably won't get a flor with standard wine yeast. In fact I'm pretty sure that you won't; there's a unique genetic pattern to flor yeasts. BTW S cerevisiae beticus was originally thought to be a separate species, S beticus. It naturally occurs on grapes. Having accidentally created a flor myself, I'd say that you can also find it on raisins. The waxy cell wall should make it fairly resistant to the drying process.

Nutritional requirements:

http://www.ncbi.nlm.nih.gov/pmc/article ... 54/?page=1

It isn't just down to oxidation either - the yeast works aerobically on a finished wine to produce aldehydes, which is why there is an airspace in the barrel. However, the flor itself blocks oxygen from affecting the wine directly; aerating the wine is unlikely to produce the same effect. The yeast needs an alcohol level of 14.5%-16% ABV to survive. Below that level the waxy cell walls do not form and you don't get a cap; it may also do odd things to the wine. Above that, the yeasts die and the wine becomes an oloroso.

I'd presume, from basic chemistry, that the yeasts are converting alcohol to aldehydes, which is probably why the sherry cask is periodically topped up with the base wine. It also produces glycerol. Eventually the yeasts die due to lack of other nutrients, and autolyse, which adds even more flavour compounds to the sherry.

Kevin

 

[evanvine]

Transfer some yeast (Live Yeast is a great antioxidant )

And so too I believe is Sulphur Dioxide, Campden Tablets/ Sodium Metabisulphite.

 

[shocker]

There was a thread on this recently :

viewtopic.php?f=23&t=20622&p=198537&hilit=oxygen#p198537

from what everyone said there didnt seem a lot of point pumping air or oxy into small brewlengths , even so its simple enough to do with an IV filter and line from e bay , aquarium pump and ceramic stone . Easy enough to sterilise too . But like was said - whats the point when stirring or whisking will do the job ? Now if we wee talking 100L plus lengths , well THEN it might be a good idea....