'If there is much less glucose, then Saccharomyces yeasts can not restart....

A note from the Cornell Enology Group with the following footnote from another email. This is where I got the 'Glucose is the same as dextrose'. Thomas Henick-Kling is no longer at Cornell, but his information is and will continue to be appreciated.

'If there is much less glucose, then Saccharomyces yeasts can not restart the fermentation. Apparently Saccharomyces need some glucose (same as dextrose) to be able to transport the fructose into the cell and ferment it.

In these cases where the glucose concentration is less than half of that of fructose, the only way to restart the fermentation is to add more glucose (same as dextrose).

None of the repair yeast (all offered so far are Saccharomyces) can restart a fermentation without an adequate glucose-fructose ratio.'

So, that given...The amateur has no means of determining a glucose fructose ratio, so we use dextrose in the starter solution.

One of the problems a winemaker may have is a stuck wine. 

After harvest and after the initial fermentation, we get several calls for 2 major problems facing the winemaker in this early stage of winemaking. One of these problems is the wine getting stuck, just quitting, sometimes prematurely. "My wine hasn't bubbled in a long time. What do I do if it is stuck?" The second problem is the rotten egg smell. Both of these issues can probably be avoided by the use of yeast nutrient added prior to fermentation.

Take a hydrometer reading and try to restart.

If a stuck wine doesn't restart by moving to a warmer room, test the SO2 level of the stuck wine with a Titret SO2 test kit. If it is above 80 ppm your efforts to restart will fail. Test the sugar level. If using a -5 to +5 hydrometer and the reading is below a -1.5 degrees or -2 degrees brix, then the wine is dry and not stuck. If the hydrometer reading is higher than a -1.5% sugar, such as a 0 reading or a plus 1 degrees, then there is residual sugar and one may attempt to restart.

It may also be lacking nutrient. Add yeast nutrient in the recommended amounts, then rack as the yeast also need oxygen in order to start, even though the whole process of fermentation itself is anaerobic. Racking will aerate.

If it does not restart on its own, make a yeast starter. We recommend using Lalvin KIV 1116 or EC-1118. These are strong yeast with good SO2 and alcohol tolerance. They produce a protein, which is capable of inhibiting or killing sensitive yeast. If the original yeast used was either Lalvin KIV 1116 or EC-1118, then use that to make your starter.

Make a quart starter using 3 parts of wine or juice and 1 part non- chlorinated drinking water, plus a pinch of yeast nutrient OR skip the nutrient at this point if using juice and one tablespoon of corn sugar (dextrose). Re-hydrate the yeast according to package directions. This is important to do as it returns the yeast cell to a healthy, more functioning condition. Rehydration in plain non-chlorinated water should not be for longer than 10 to 15 minutes. Add the rehydrated yeast to the wine/juice and water, sugar mix.  Shake to aerate. Oxygen is beneficial in getting the fermentation going.

This starter will take one to three days to become active. When active, remove one half quart of wine from the carboy, reserve. Replace this volume with half quart of the starter. Add the wine removed from the carboy back into the starter. When the starter gets going again and if the carboy is not, repeat the procedure. There will not be a violent fermentation as there is not a lot of sugar available. Keep going and good luck.