"flowerpot" > wrote in message
ups.com...
> 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

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