This article is from the WineMaking FAQ, by malak@CAM.ORG (Don Buchan) with numerous contributions by others.
If you wish to increase your alcohol content, such as for ports,
sherries and the like, try syrup feeding and using champagne yeast.
Prepare your must like a regular wine (but keep your initial sg below
1.095) and ferment using a high alcohol tolerant yeast. Rack to
secondary as usual at 1.010. When the sg is at 1.000, bring it up to
1.010 with a 2 to 1 sugar to water syrup. This can be done several
times, but production will usually stop at roughly 18%. Don't worry
about excess sweetness if you're careful as higher alcohol levels tend
to mask sweetness and sweetness tends to smooth out the rough taste
from higher alcohol levels; as well, in order to get the same apparent
sweetness as a wine with a given lower alcohol level, you need more
residual sugar. If you put in too much sugar, A) learn to live with a
slightly sweet wine and B) experiment to see what works best for you in
Most port is made by stopping the fermentation by adding of high alcohol
brandy. Start your wine in typical fashion (add yeast or spontaneous),
watch your residual sugar closely and add brandy when RS is at desired
level (usually 8 to 10 brix). Add brandy to 19%. Pure brandy is
difficult to obtain for the home winemaker, and some fine ports made
with grain alcohol, while some would disagree.
If brandy is added while skin fermenting, add brandy to 17% (enough to
kill the yeast), press your must, then correct to 19%.
According to "The Lore of Still Building" by Kathleen Howard and Norman
Gibat, you can concentrate the alcohol (and everything in the wine as
well) by putting the wine in a freezer until it turns mushy. It can
then be poured or ladled into a large strainer cloth and squeezed dry.
The liquid squeezed out will be higher in alcololic content than the
residue in the strainer cloth. This method should yield a fortified
wine (20% to 30% alcohol) from ordinary wines. Unfortunately, the book
does not give a good indication of freezer temperature or how long the
wine should be frozen.
Please note that this is effectively the same as distillation and can
be quite dangerous with regards to methanol concentration.
The Pearson Square
Spirit is expensive so you will need to calculate the correct amount to
achieve the desired result.
The Pearson Square is useful if you are using your own wine, plus some
Polish Spirit and some of the excellent flavorings now available on the
market to make liqueurs.
THE PEARSON SQUARE
A B C D E
(A x B) + (C x D) ----------------- A + C
(2 x 15) + (3 x 10) 60 ------------------- = -- = 12 2 + 3 5