Primary container?

If you are talking about putting a plastic bag over the bucket for the first week or less of fermentation, during that stage you do not need to seal the bucket. It is sufficient to just cover it with cloth to keep bugs out. I just cover it with a clean towel.

Ray

It defeats the purpose if you seal the primary fermentation bucket in a plastic bag.

You need air for the primary fermentation so the yeast can multiply quickly.

: > Many thanks : > flowerpot : >

: :

But I thought contact with oxygen had to be limited and the must should be protected beneath a blanket of carbon dioxide?

flowerpot

In early stages, yeast need O2 to reproduce. When you make wine from fruit, you keep it in a vat or primary and several times a day you stir the cap (the fruit pulp that rises to the top) down. This prevents mold from growing on the pulp and it aerates the must. After about 3 to 7 days the cap will fall, which means it stops rising back to the top. After this point it becomes much more important to protect it from O2 so you put it under a airlock from that point on.

Another way to put it is that the end products of fermentation need to be protected from O2. Those are not present at the beginning of fermentation. But after a few days you must start protecting it. With fruit wines, the indicator people use to determine when you must start protecting it is the cap falling. With wines made from pure juice, it is up to you as to when you start protecting it.

Ray

Thanks for the explanation, Ray. I had assumed there would be enough dissolved oxygen already present in the liquid for the yeast.

Many thanks flowerpot

Flowerpot wrote "But I thought contact with oxygen had to be limited and the must should

You're right Flowerpot ( do you have a real name...it's hard to talk to a flowerpot ). Here's a neat trick. Start your wine in an open container covered with a sheet of plastic or towel like Ray says. This lets enough air be in contact with the wine so the yeast are happy. Hold a lit match under the cover and see if it goes out. If it does there's a lot of CO2 being produced by the yeast. Near the end of fermentation you will have to hold a lit match close to the surface of the wine before it goes out. That's the time to rack the new wine to a FULL carboy and stick an air lock on it to protect it from further contact with oxygen.

Bill Frazier Olathe, Kansas USA

You are right Flowerpot.

Most wine yeast strains need from 5 to 20 milligrams of oxygen per liter of juice to produce a large population. Grape juice becomes saturated with oxygen during normal crush operations, and saturated juice contains about 10 milligrams of oxygen per liter. If enough sulfur dioxide is added to deactivate the exzymes, the dissolved oxygen remains in the juice for some time. Consequently, little extra oxygen is required by the yeast for normal fermentations. Even so, some winemakers prefer to stir and splash juice a day or two after adding yeast to provide a bit more oxygen. They hope the additional oxygen will promote more rapid and complete fermentations. (Sometimes stuck fermentations can be restarted just by racking and splashing the juice to introduce a new supply of oxygen).

Lum Del Mar, California, USA

Are you talking about putting the bag over the bucket as a kind of loose seal? If so sure, my grandmother used to make small batches in bottles with ballons over them. Back then airlocks were made of glass and she never knew they existed...

You have already gotten a lot of good advice; I just wanted to address the initial question if I understood it correctly.

Joe

Yes I've always wondered at what stage the yeast fermentation changes from an aerobic stage ( yeast growth) to an anaerobic ( CO2 productoin) stage, and if it was possible to regulate alcohol production from a given amount of sugar by sitrring the must and promoting more of an aerobic response.

I cover with a good cloth and plunge the cap daily. This keeps the cap moist and helps prevent acetobacteria from growing. I also use this stage to extract colour and tannins.

Current information indicates that yeast do not really use respiration (aerobic) when we're talking about wines. The sugar content in the must is usually high enough that the yeast favor fermentation because of the speed at which they can obtain the energy. The only time they really respire is when there is limited sugar, but in a wine fermentation, by the time the sugar is depleted to this level, the O2 is gone and the alcohol is high, so the yeast still favor fermentation.

The old, aerobic vs anaerobic "stages" don't really happen. The introduction of O2 is really to keep the yeast healthy by giving them some raw material to help maintain the cell wall during growth. Unless you significantly underpitch or use unhealthy yeast, there should be enough disolved O2 in the must just from the crush operation.

Andy

Right? Is there really a right way and a wrong way?

I think I would be more inclinded to rack the wine off the solids first directly into the secondary, then just pour the solids into the cheesecloth to extract the remaining wine. This should reduce your exposure a bit.

Yes.

I would, but you may want to test the free SO2 first.

Andy