I'm still hesitating over making wine from the grapes in my garden, having made kit wine in the past that was disgusting (it tasted of bananas). So I am on the lookout for tips and encouragement.
I made a drinkable white wine from my garden grapes - so a few pointers:
1. You'll need about 20lbs of grapes to make one demijohn of wine. If you have less, you could use it to blend into an apple wine.
2. The grapes must be pressed - if you blend them the seeds and skins will impart unpleasant flavours and excess tannin.
3. You could tread the grapes to press them, but I got by with pressing them by hand through muslin-lined colander, with the aid of a potato masher. It does take a while, and don't forget to boil the muslin as it's a bacteria trap.
4. The must will almost certainly need to be chaptalized (have sugar added) as outdoor grown grapes in this country don't develop enough of their own. You're looking for a gravity of 1080-1095. Mine was about 1060 so I added heavy sugar syrup to bring it up. There are online calculators so you can work out how much to add. So a hydrometer and trial jar is essential.
5. Leave the must and sugar, a crushed campden tablet and some yeast nutrient to stand for 24 hours in a covered sanitised bucket, then aerate well with a sanitised whisk, and pitch the wine yeast. After a few days you can rack it into a demijohn and leave to ferment out. Try to keep fermentation at a steady temperature of around 20 degrees. The banana flavour you mentioned can occur if you've fermented at too high a temperature.
6. Once all fermentation has ceased rack it again to get the wine off the dead yeast. You can measure the gravity at this point to calculate the alcohol content. I then left it in a demijohn for a few months before bottling.If you have an air gap due to the racking, top up with some white wine (preferably) or boiled cooled water
7. The wine I made was minging at first, but became quite pleasant after six months, and better still after a year.
8. A general tip: beer and wine making is mostly about cleaning and sanitising.