So I've just finished sorting this out.
After sanitising the bucket, I put 1 litre of red grape juice in minus 100mls. Then I added the rest of the steamed juice that was in the earlier picture.
The 100mls of red grape had 1/4 teaspoon of the GoFerm rehydration nutrient stirred into it and it was then placed in a small bath of hot water and I put my digital thermometer in it. The normal temperature for rehydrating Lalvin yeasts is 40C, but I only let it get to about 38C before pitching the yeast and giving it a good stir.
The main part of the must in the bucket was sampled to check the starting gravity, which measured 1.120 so I should get about 14% ABV from that. At the same time, after a bit of messing about (new battery) I got a pH reading of 3.31 from the must. So it's not as acid as I thought it might be. I like to keep my musts in the region of 3.5 pH so I stirred a teaspoon of calcium carbonate into it - apparently, my friend in Oklahoma emailed me and said that it's better if I used Potassium carbonate as it's less likely to cause any "after taste", but the calcium carbonate a.k.a. precipitated chalk, is all that the home brew shop had. Also, apparently "Cream of Tartar" is also good for neutralising acids as well.
Normally when rehydrating yeasts, you're supposed to leave it for no longer than 15 minutes according to the packet, but there was a hell of a head of froth on it after 10 so it just got swirled back into suspension and pitched into the must.
As soon as I see any signs of fermentation, I'll be adding the main nutrients of the Fermaid-K and DAP. I've just got to work out how much, though I'm thinking of 1/2 teaspoon each at the moment....
Watch this space.....