oxidation- a myth

[guy poppe]

I'm a relative novice at beer making but religiously read this forum and others to get information.

One of the subjects that perplexes me is oxidation.

So far, I gathered the following principles:

1. No need to worry about oxygen when the wort is still hot.

2. Get the wort cool quickly to avoid exposure to oxygen

3. aerate the wort before pitching

4. do not expose ferment to air

5. reduce exposure when transferring and bottling

6. some brews (Belgian) are fermented in open air

7. One writer expermimented with air vs. no air prior to fermentation and saw no difference in fermentation activity

8. yeast needs air to propogate

9. cardboard taste is a result of oxidation

I can appreciate that exposure invites infection, an thus the above principles. However, is it truly necessary to aerate before pitching? I have never done it and my fermentation is always immediate.

o.k. you experts, explain this to me

Best Regards

Guy L. poppe

[munkey]

firstly your post is unclear, are you suggesting that oxidation is a myth, or that aireation of the wirt is uncalled for?

i will comment on both thease in any case, firstly i dont think oxidation is a myth, why on earth would it be, scientificly and in chemical terms there are chemicals in beer that will combine with oxygen and create other compounds, weather or not theas will make the tastes noted in the effects of oxidation or not is something i have no exsperiance of, but none the less your beer will change chemicaly if exsposed to oxygen.

secondly areation of the wirt is something that is mainly need for full mashers , as the full mash process (espechaly boiling the wirt for a hour) removes oxygen from the mixture, it dosent take much for water to re-absorb o2 so sometimes just agitation (eg. splashing the cold wirt into the fermentor) will do.

hope this helps.

[Rubber.Piggy]

Hi Guy, I can answer a couple of your points for you

6. some brews (Belgian) are fermented in open air

Carbon dioxide is heavier than air (oxygen and nitrogen) so you will find that even in an open fermentation a cloud of co2 sits over the brew (assuming your not disturbing it) and protects it from other gases.

8. yeast needs air to propogate

This is true, hence why the propogation phase is called the aerobic phase. During this phase the yeast consumes all the oxygen and multiplies. Once it runs out of oxygen it stop multiplying but continues to ferment (the anerobic phase), I think both pahses produce carbon dioxide and alcohol. This would suggest that the more oxygen in the wort at the start, the more yeast cells you end up with...

As munkey said for extract brewers splashing the wort into the fermenter (what I do) should give enough oxygen for a good brew.

9. cardboard taste is a result of oxidation

As I understand, the time to avoid oxygen is during bottling, i've never experienced the infamous cardboard taste so I guess my quiet bottling is working

I can appreciate that exposure invites infection, an thus the above principles.

Exposure to oxygen?? Exposure to oxygen it self will not increase your chance of infection. Increased infection risk comes from exposeure to unsanitised surfaces and ingredients. I would venture that if your air is dirty enough to increase your infection risk, you yourself would know because you would be sick.

However, is it truly necessary to aerate before pitching? I have never done it and my fermentation is always immediate.

I would suggest that if you have not been specifically aerating your wort and you have been getting good results, then your wort has enough o2 in it already simply from your method and ingredients. If your method produces results that you are happy with there is no need to change it.

EDIT: words missing :p

[chris.]

1. No need to worry about oxygen when the wort is still hot.

This is debatable. If your refering to oxygenation - Yes I believe it to still be an issue when the wort is still hot. I personally try to keep oxyen out of the wort until it's cool (try a search on hot side aeration).
If your refering to contamination by airbourne bacteria etc. then I believe it's still an issue while the wort is cooling. I keep the lid on the pot at all time's when cooling.

2. Get the wort cool quickly to avoid exposure to oxygen.

Getting the wort as cool as possible as quick as possible will help to limit bacterial infection & lower DMS levels.

3. aerate the wort before pitching.

Yeast need Oxygen to reproduce. Aerate the wort once its cooled prior to pitching.

4. do not expose ferment to air.

I good idea in my opinion. It helps to limit infections.

5. reduce exposure when transferring and bottling

This helps to prevent infection also.
Try to avoid splashing & introducing Oxygen into the wort. This will cause oxdisation if you plan on storing the beer for extended periods.

6. some brews (Belgian) are fermented in open air

Lambic beers (among others) are open fermented. There are also plenty of other types of beers fermented open. Some believe that closed fermentations produce too much pressure in the fermentation vessel & that this stresses the yeast.

7. One writer expermimented with air vs. no air prior to fermentation and saw no difference in fermentation activity

I'm not sure on this.
I've heard interviews with Chris from whitelabs & Dave from Wyeast & both recommend limiting the pressure in the fermentor by not using an airlock just aluminium foil over the top of the fermentor.
I'd be interested in reading the article you've found.

8. yeast needs air to propogate

Yeast need Oxygen (dissolved in the wort) to reproduce.

9. cardboard taste is a result of oxidation

I can appreciate that exposure invites infection, an thus the above principles. However, is it truly necessary to aerate before pitching? I have never done it and my fermentation is always immediate.

It is not necessary to aerate the wort as long as you pitch big enough amounts of yeast, or there's already a fair amount of dissolved oxygen in the wort. The main reason the yeast require oxygen is for reproduction.
If your making beer from kits & using say 20litres of tap water then you don't have to worry as much as someone who's doing a full 25litre boil (boiling releases the oxygen out of the wort) as your tap water will contain a small amount of oxygen.
However if you want to give the yeast the best start you can it's advisable to aerate the wort before pitching (and sometimes again afterwards if the OG is high).
Either way you will make "beer"

[Chris]

Guy,

the best thing to do when you get seemingly conflicting advice, is to simply try it yourself. Once you find the way you like it, you can experiment furthur, or stick with it.

Don't be afraid to just give it a go.

[chris.]

Guy,

the best thing to do when you get seemingly conflicting advice, is to simply try it yourself. Once you find the way you like it, you can experiment furthur, or stick with it.

Don't be afraid to just give it a go.

Well put Chris.

If your happy with the results of your process then stick with it.

But don't let that stop you trying for something better.
Read up, cross reference, & experiment.

[guy poppe]

Thanks for all for the information. I should have put a ? atfter "Myth" in the heading.

What intrigued me was the concept of yeast needing oxygen to redproduce, yet except when pitching, we seem to take all measures to avoid exposing the yeast. Does it not run out of oxygen? Where does it get oxygen to produce CO2?

I did some more reading and one writer said oxygen is only needed in the initial stage then the yeast turn anarobic.

If that's true, fascinating that a creature can live both with and without oxygen.

Regards

Guy Poppe

[BeerFrenzy]

If that's true, fascinating that a creature can live both with and without oxygen.

Sure is. Microbiology in general is fascinating. Here is a link to brewing and the role yeast plays in the process:

http://www.yeastgenome.org/community/ArtOfBrewing.htm

[Rubber.Piggy]

Does it not run out of oxygen? Where does it get oxygen to produce CO2?

It runs out of oxygen gas (o2) but there is oxygen, carbon and hydrogen attoms in the carbohydrates (sugars). As rule of thumb when you break big organic molecules (carbohydrate) into smaller ones you get co2 and water as by-products. In this case the yeast "digests" the part of the carbohydrate it wants and leaves the rest behind, the pieces are alcohol, co2 and propably some water too.

This is a simplified explanation, track down a first year uni microbiology book if you want to know more. High school chem and first year uni chem books will tell you more about organic chemistry.

[guy poppe]

Thanks Beer.piggy and Frenzie.

I didn't want to learn that the CO2 is actually comes from the yeasties' urine.

Gives new meaning to "getting pissed", pardon the language but couldn't resist.

Now I wonder if the yeasties also get plastered. What a life!!

Regards

Guy Poppe

[Oliver]

Some believe that closed fermentations produce too much pressure in the fermentation vessel & that this stresses the yeast ...
I'm not sure on this. I've heard interviews with Chris from whitelabs & Dave from Wyeast & both recommend limiting the pressure in the fermentor by not using an airlock just aluminium foil over the top of the fermentor.

I'm not doubting that they said this Chris., but I find the concept intriguing.

Surely the minimal increase in pressure caused by having an airlock fitted pales in comparison to the pressure that yeast would be exposed to at the bottom of the wort (caused by the sheer weight of liquid above it), even if there was no airlock fitted. In fact I'd reckon the pressure even a few centimetres down in the wort would be greater than this alleged extra pressure caused by an airlock.

There may be reasons that having an airlock fitted during fermentation cause the resulting beer to taste different, but I find it hard to believe that any increase in pressure would be the cause.

Thoughts, ladies and gentlemen?

Cheers,

Oliver