Aeration are we really adding oxygen?

[revjester]

On several posts I read about shaking or stirring to get oxygen into the must for either the first 3-5 days or up to the 1/3 sugar break.
But I've been thinking.
When we start, yes we put in oxygen.
After a day if fermenting with the airlock bubbling the must is putting Carbon Dioxide into the little headspace left and pushing the oxygen out. So if I pick it up and shake it where would the oxygen that I am supposedly mixing in coming from? Every day after it would be less likely to have any oxygen in the must or the headspace.
Now I am not saying don't shake or stir. Obviously it does degas the must, which is a good thing. Any yeast on the bottom get back in suspension. And for all I know, the yeast are really happy to be swirled around and it is all about keeping the yeast happy.
Some folks put in pure oxygen with a wand and aeration stone. That most likely gets oxygen in, but since most people don't, I am not sure it is necessary, but what the heck, it works for them, I won't knock it.

 

[Elfmaze]

subscribing to hear other opinions... I only introduce oxygen, if needed, at the very beginning after cooling the wort.


I would think you would not want the yeast to have oxygen available later in the fermentation because that would allow them to respirate in stead of ferment as the wort sugars get lower.

Yeasts only sometimes need oxygen and that's just in the very beginning if they do not have a good lipid supply, yeast nutrient or cold break fats. I don't know about continuously giving them oxygen?

 

[Yooper]

Really, when you are stirring the primary you aren't so much adding oxygen- it's more about the degassing. Co2 is poisonous to yeast, so stirring well to get rid of much of it improves yeast health, and the stirring probably introduces a small amount of oxygen. With mead, since it's a tough ferment as a rule (honey has very little in nutrients for the yeast), degassing and adding nutrients through the sugar breaks helps keep the yeast healthy.

 

[bernardsmith]

Don't yeast need oxygen in order to reproduce? Can't speak for those brewing beer but wine, cider and mead makers tend to ferment in buckets covered with cloth for the first few days and we stir our must to incorporate air. We add an airlock only when we rack, and we rack when the gravity has dropped close to 1.000 , when the most active fermentation is slowing down and the CO2 being produced by the yeast has dropped. What works for brewers works for brewers.

 

[Yooper]

Don't yeast need oxygen in order to reproduce? Can't speak for those brewing beer but wine, cider and mead makers tend to ferment in buckets covered with cloth for the first few days and we stir our must to incorporate air. We add an airlock only when we rack, and we rack when the gravity has dropped close to 1.000 , when the most active fermentation is slowing down and the CO2 being produced by the yeast has dropped. What works for brewers works for brewers.

Yes, they use oxygen to reproduce. But often stirring degasses (gets rid of poisonous c02) which is beneficial as well, perhaps more so.

 

[bernardsmith]

Yes, they use oxygen to reproduce. But often stirring degasses (gets rid of poisonous c02) which is beneficial as well, perhaps more so.

I imagine that "degassing" reduces the pH level a little too as presumably CO2 will form carbonic acid.

 

[revjester]

Sure in a primary bucket, people stir. But CO2 is heavier than O2 and the bucket will be full of it. Stirring may scoot some of the CO2 out and let a little O2 into the bucket but how much is really getting down into the must. Plus with all the CO2 coming out is there any room to dissolve the O2 into the must? I believe aerating is a good thing, I just don't believe it gets the oxygen into the must.

 

[Elfmaze]

ops sorry, I didn't realize I was in the Mead forum there with my response. I'm guessing mead does not have the lipids necessary for cell wall building as much as beer wort does? maby hence the extra oxygen needs?

 

[Yooper]

ops sorry, I didn't realize I was in the Mead forum there with my response. I'm guessing mead does not have the lipids necessary for cell wall building as much as beer wort does? maby hence the extra oxygen needs?

Generally, it's because mead is a very high ABV and that alone can stress yeast. That, combined with the low nutrients in the honey, mean that some pampering is done to keep the yeast happy. Co2 is poisonous to yeast, and can really stress them and the amount produced with a vigorous ferment is enough to slow fermentation so degassing is a great idea for high OG musts, especially when fermentation is active.

Once fermentation slows and the mead (or wine) is vulnerable to oxidation, often about 1.020 or less, the mead is airlocked at that time.

 

[Yooper]

I imagine that "degassing" reduces the pH level a little too as presumably CO2 will form carbonic acid.

The yeast are most responsible for the pH in the mead, but if you stir off some of the co2, it can help raise (not lower) the pH a tad.

 

[bernardsmith]

The yeast are most responsible for the pH in the mead, but if you stir off some of the co2, it can help raise (not lower) the pH a tad.

Of course. Careless of me. I meant reduce the acidity a hair (and so raise the pH)

 

[biochemedic]

Oxygen is indeed important to yeast metabolism, and having some oxygen in solution at the start of fermentation is beneficial. I am one of those who does the whole oxygen/diffusion wand thing at the start of fermentation, and I did notice improvement in my overall fermentation after starting to use it. After reading the book Yeast, I was convinced that simply agitating/swirling/sloshing or other mechanical means just didn't get the adequate amounts of oxygen needed.

 

[fatbloke]

Oxygen is indeed important to yeast metabolism, and having some oxygen in solution at the start of fermentation is beneficial. I am one of those who does the whole oxygen/diffusion wand thing at the start of fermentation, and I did notice improvement in my overall fermentation after starting to use it. After reading the book Yeast, I was convinced that simply agitating/swirling/sloshing or other mechanical means just didn't get the adequate amounts of oxygen needed.

Which is fair enough. Yet as long as any CO2 blanket has been disturbed/removed, any small quantity of O2 you might manage to get in has got.to be helpful.

Personally, if it's feasible, I use a stick blender or balloon whisk - and when there's fruit I don't want smashed to bits, I've even taken a litre or so out and blitzed it in a sanitised liquidiser and then added it back, all to no effect other than getting some O2 in.........