wrote:

On Jul 14, 3:27*pm, Adam Funk
wrote:
My main reference book for winemaking is Duncan
& Acton's _Progressive Winemaking_ (1967).

It says that the initial SG of a must should
generally be below 1100, and that feeding sugar
syrup later is required for wines over 14% ABV.
It's recommendation for feeding is to add 4
ounces of sugar per gallon (dissolved to make
sugar syrup), when the SG is between 1000 and
1005, to be repeated as required when the SG is
back in that range.

But this book also says "most yeasts can
produce at least 10% alcohol", which sounds a
bit out of date.

I'm using Gervin No.3, which is supposed to be
fairly alcohol-tolerant (up to 18%, I think)
and suitable for dessert wines, to make a wine
based on Pomegreat (a pomegranate juice blend,
which contains about 100 g/l of natural sugar).

I think the feeding rate of 4 oz per gallon at
a time sounds rather conservative. *Are yeasts
generally "tougher" than they were then? What
is the contemporary rule of thumb for this?

Thanks,
Adam

--
It is probable that television drama of high
caliber and produced by first-rate artists will
materially raise the level of dramatic taste of
the nation. * * *(David Sarnoff, CEO of RCA,
1939; in Stoll 1995)


If you are using a yeast strain to achieve a
particular goal (i.e. many yeasts can have an
impact on flavour, acid levels, H2S risk, etc),
then it is more important to use the desired
yeast and make sure you don't kill it with sugar
or alcohol.

Note that it is not only the eventual alcohol
level that is the problem, but the fact that too
high a concentration of sugar in the
must can also be toxic to yeast. So, just
because a yeast can handle 16% or more alcohol
in the finished wine, doesn't mean that it can
handle the high-sugar environment of the initial
must.

Now, it tends to be the case that high alcohol
tolerance goes hand-in-
hand with sugar tolerance, but that is not
always true. In the case of Gervin No. 3, I'm
pretty sure it is rated for up to 18% alcohol
and is also recommended for dessert wines (i.e.
very high initial SG), so you're good to go.

In general, you need to check the specs on the
specific yeast you are using, and think about
what your goal is in using the yeast.

It is also a good idea to check the specs on the
optimal temperature range for the specific yeast.
I learned this the hard way.