"Dave Allison" wrote in message
.. .
I've done it, and not done it. Doesn't seem to affect (effect?) the
results. Kits are special things. smile. Follow instructions and they
work - they want them to work so you will buy more. I've done over 18 now.
DAve

wrote:
On Mar 26, 3:18 pm, Wayne Harris wrote:
Kit wines from Concentrate.

While there is no "cap" to punch down during primary fermentation,
does it make any sense to stir in the foamy top occaisionally?

It never hurts to aerate the fermenting must in the first few days.
Yeast thrives on 02 in the initial stages.

My understanding is that the only thing yeast really "does" in life with the
energy it extracts from sugars is multiply. In the process, it converts the
sugars to waste products (from the yeast's point of view). Those waste
products differ when the yeast has O2 versus when it does not.

If yeast is working aerobically (in the presence of O2), it can extract
roughly 18x as much energy from a sugar molecule as it can when working
anaerobically (no O2). Thus it should be able to multiply a lot faster when
O2 is present, because the metabolic pathway it can use then is so much more
efficient. However, the cost of this is that the sugar it consumes
aerobically is converted to CO2 and water, rather than CO2 and alcohol. So
basically by aerating you will be accelerating the initial multiplication of
the yeast at the cost of slightly more water and less alcohol in the final
product.

There is also the issue of what oxidization does to the flavor of the wine.
Oxygen is an extremely corrosive element that reacts with just about
anything, including many of the flavonoids, etc., in the must. To much O2
exposure will lead to a substantial difference in the flavor of the wine.
Whether you think it makes it better or worse is a matter of your own
personal preference. (The experts will say it makes it worse, but do you
drink wine based on what other people tell you they like, or what you like?
:-)

Kevin