I wasn’t planning on making any wine this year – well, certainly not with my own grapes, but a very kind viewer of my blog contacted me and offered some of their grapes. They had such a bumper crop this year in their garden that a lot of them would have ended up going to waste. So I went round last week and they helped me to harvest about 15kg of red grapes (of unknown variety). I had decided that I’d like to make 2 demijohns worth (about 10 litres) and the rule of thumb is that you get approximately 2 thirds of the weight of grapes in kg, in volume of juice in litres. So to get 10 litres of juice I would need about 15kg of grapes.
As soon as I got them home they were stripped off the stalks and then crushed. I don’t have a crusher so opted for the good old fashioned approach of treading them (having given my feet a good wash beforehand!)
The grapes tasted quite sour and I suspected they weren’t really ripe enough. I’m not sure that waiting any longer to harvest would have helped as we’re so close to the end of the season. I think the main problem is due to a combination of the British weather not being fantastic for ripening red grapes, and the fact that there were a huge number of bunches of grapes on just one vine. It is better to have more vines with fewer grapes than fewer vines with more grapes. As grapes ripen the acidity reduces and the sugar content increases, and there is an optimal point at which the two are in the right area and so the grapes are ready for harvest. I am looking for a specific gravity (SG), and hence sugar content of around 1085 and a pH of about 3.5 Testing the SG of these grapes gave a reading of only 1062, which would give a wine of 8% alcohol and a pH of 2.9, so definitely under-ripe.
Adding sugar is the easy way to get around the low SG, so I added enough to bring it up to 1082 which should produce a wine of 11% alcohol.
The high acidity is a bit more tricky to deal with and can be lowered by adding calcium carbonate, but I’ve never tried this before so have decided not to at this stage I have chosen a yeast (Gervin GV11) which supposedly has the potential of metabolising up to 30% acid, so it will be interesting to see if that helps in any way. Although the must doesn’t taste too bad now, the problem with too much acidity is that all the sugar (which is good at masking sour tastes) ends up being converted to alcohol so you end up with a very sour tasting wine.
I’ll see how it turns out and work out what to do later if it really is too acidic.
So having crushed the grapes and added 0.5g potassium metabisulphite (to kill any wild yeasts and other bacteria) I left if for a day and then added the yeast and yeast nutrient.
I then stirred the must 2 or 3 times a day to oxygenate it and stir in the skins which end up being forced up to the top due to the carbon dioxide produced during fermentation. As soon as I think enough colour has been extracted from the skins I can put it through the press. Leaving it on the skins for longer increases tannin levels, but can also introduce bitterness from the pips. As I already have a potentially acidic wine I’ll keep the skin contact fairly short, maybe a week, which means pressing tomorrow.
The following two pictures show the must fermenting away nicely before and after stirring, showing how the cap rises during fermentation.
