Select tender, freshly dug parsnips, and scrub them carefully to remove every trace of soil. Top and tail them, cut into small cubes, place them in a pan together with as much of the water as you can. Bring to the boil, cover and simmer until the parsnips are quite tender but not mushy. Leave to cool.
Strain out, drain well and discard the parsnips. Stir the concentrated grape juice into the liquor together with the citric acid, tannin, nutrient and an active yeast. Pour the must into a jar leaving room for the sugar. Fit an airlock and ferment for seven days in a warm place, 24°C.
Remove half the must, stir in one third of the sugar and when it is completely dissolved, return the must to the jar, replace the airlock and continue with fermentation.
After a further seven days, repeat the process with half the remaining sugar and, seven days later still, add the remaining portion in the same way.
When fermentation is finished, move the wine to a cold place for a few days to help it to clear, than rack it into a clean jar, top up, if possible with vodka, if not with another white wine or cold boiled water.
Store this strong, sweet, dessert wine for at least one year in a warm place and preferably after bottling, keep it for a further year.