Relationship between yeast and oxygen

[Noontime]

I've seen a lot of posts lately extolling the virtues of oxygen exposure during fermentation, and although I'm not an expert I wanted to share a little bit of info from a layman's level of understanding.

Fermentation is by definition an anaerobic process, meaning the conversion of sugars to alcohol is done without any oxygen.

Yeast do need a tiny bit of oxygen to build their cell walls, but it's something like 10 parts per million. Before it really gets going and it's building up a colony, the must should be allowed to “breathe a little” until alcoholic fermentation starts. So gentle stirring and punch downs are more than enough.

Although CO2 saturation helps keep things from getting oxidized, actively trying to incorporate oxygen into the must is probably a bad idea.

I just wanted to throw that information out there. Thanks!

 

[Jswo23]

Noontime, Please see both my threads Airlock overflow and 1gallon batch in a 2 gallon fermentor, i would love your input so i dont lose either of my batches!

 

[Tnuscan]

A wise man once posted,

"I agree with just covering with a towel is a better practice, but it would have been just fine to do the whole fermentation under airlock. The yeast would have used aerobic metabolism/reproduction until they exhausted the oxygen dissolved in the must and in the headspace, and then switched to anaerobic fermentation/metabolism afterwards."
__________________
Paul - AKA- [ sour_grapes]

 

[Scooter68]

Initially I used the plastic covers and airlocks but found my fermentations cranked up a little better under the cloth. (My concern initially was about evaporation of alcohol out of the must. - to which a lot of old hands on here told me pffft - not enough will be lost due to the CO2 blanket that will form. So I changed to the cloth covers.)

BUT in reality the cloth covers are so much easier to fit on and off when I need to punch down my fruit bag, stir the must to keep it well mixed, and to do the SG checks on the must. Plus the plastic lids don't always make a complete seal so the Airlock sits there and does nothing - not a problem but.. Also if the foam forms or the bag rises it just pushes up the cloth cover and no airlock cleaning required.

 

[bkisel]

I've done "primary" both loosely covered and under airlock and it hasn't appeared to make a dimes worth of difference in how the wine turned out.

 

[Julie]

The purpose of letting the lid lay loosely and just cover with a cloth is to ensure a good fermentation. Can you ferment without letting the lid on loosely, absolutely but there is a chance you might have a stuck fermentation. For me, if there is a chance at something, I wont do it. I prefer on doing everything in my power to ensure a good wine.

 

[Johnd]

While the topic is pretty simple, to allow oxygen or not, as in most winemaking chemistry, there is usually scientific information behind the simple answer of "do it this way" or "do it that way".

If you are so inclined, I have attached a pdf which I read and printed some time back, and occasionally refer to. Once read, you'll understand that you probably have plenty O2 in your wine from your initial activities of dumping juice into a bucket, manipulating grapes, stirring, etc, to get your yeast going. Understand why completely limiting O2 exposure may cause issues, why stirring and punching down can be beneficial, and why sometimes when you splash rack to a carboy near the end of fermentation, you'll sometimes see a marked increase in activity soon afterwards. It's a good read of some of the science behind our hobby, hats off to MoreWine.

http://morewinemaking.com/public/pdf/oxyfer09.pdf

 

[Tnuscan]

I've never clamped down a lid with a airlock on my pail/bucket. I really feel it can do without all the very large amounts of CO2 that is released during the aggressive part of the ferment.

Years back I smoked cigarettes but when I sat in a room filled with smokers I liked to crack a door or window open. Too much smoke became an aggravation. It really stressed me out. lol

I'm not bragging (knock on wood) I've never stuck or lost a ferment and I have made a lot of wine. Most of the posts on here and other places that have stuck fermentation or trouble with fermentation have the beginning primary vessel under airlock.

 

[Johny99]

The purpose of letting the lid lay loosely and just cover with a cloth is to ensure a good fermentation. Can you ferment without letting the lid on loosely, absolutely but there is a chance you might have a stuck fermentation. For me, if there is a chance at something, I wont do it. I prefer on doing everything in my power to ensure a good wine.

I'm with Julie. Yes it can work anaerobic. Yes there can be problems if yeast doesn't have enough oxygen. Yes raw juice has lots of o2 in it at first. However, I prefer not to take chances. Airlock as fermentation ends, and the co2 is no longer keeping the air away. Simple practice that works for me.

That said, one fun thing about wine is it is 50% known science, 50% art, and 90 % dumb luck at my winery.

Ps don't tell my consumers

 

[Brub58]

For me, if there is a chance at something, I wont do it. I prefer on doing everything in my power to ensure a good wine.

What about the chance of oxidation, which is very real (whereas a stuck fermentation due to lack of air is very unlikely)?

The morewine manual linked to above recommends 5mg/l O2 at the start of fermentation for white wines. The natural solubility of O2 in water is 8mg/l (http://www.lenntech.com/periodic/water/oxygen/oxygen-and-water.htm) so it's unlikely you need any additional oxygen for a white ferment. Their white wine manual also states "If you have access to inert gas it is highly recommended to purge the receiving vessel before it gets filled to eliminate the oxygen and avoid any oxidation reactions" when transferring the juice - before any fermentation has started.

I'm not saying always airlock - I punch down my reds like everyone else. But I have a real problem when someone with a good fermentation is told they have to take the lid off and only cover it with a towel. It's just bad advice.