I had a several email exchange with Jack some time ago on this topick when I
had a couple of batchs stick. He suggested at the time that when you are
making a low solids wine from pure filtered juice such as Welch's grape
concentrate, most of the yeast will settle to the bottome toward the end of
primary fermentation. If you carefully rack off the leas and leave all of
them behind you may end up with too few yeast to carry on an active ferment
and the yeast, which is not reproducing at this stage, may die off before
finishing ending in a stuck ferment. He never seemed to suggest this when
you are fermenting on pulp from fruit which yield gross leas.

I do not mean to put words in Jacks mouth but that is basically what I took
from his suggestions.

Ray