So, how can you tell if grapes are ready for harvest or not? Well, you can taste them, or you can measure sugar and acidity levels. The best way is probably a combination of the two. As the grapes ripen, the acidity falls and the sugar level rises, until the two are at just the right point, and the grapes are ready for harvest. I have been measuring the sugar levels over the past few weeks using a refractometer:
A few drops of juice are placed on the prism (the blue bit) and when you look through the eyepiece a shadow indicates the reading. Here is a view taken through the refractometer, showing a reading of 22.5º Brix or 1.094 SG.
This is a great piece of kit as not only does it give a quick guide to the sugar level, it does so using just a few drops of juice, and so doesn’t waste too many grapes. The recommendation is to take several grapes from different vines from different parts of the bunch to get an average, but I don’t really have enough grapes so I’ve just been picking a single grape at random.
Measuring acidity is a bit more tricky as it requires at least 5ml of juice, which isn’t a lot, but since you need about 10 grapes each time, I’ve not bothered to do this with the Phoenix or Orion to save as many grapes as possible for making wine. As I only had a few bunches of Solaris I decided not to even bother using those for wine and just make a bit of juice, testing for sugar and acidity.
It tasted delicious. Very sweet. The final measurements were 1.094 SG and 1% TA.
SG is Specific Gravity and is the measure of density of the juice (where 1.000 is the density of water), which can be translated into amount of sugar in the juice, and therefore potential alcohol level of the finished wine. 1.094 is really high and gives a potential alcohol level of about 13%.
TA is the Total Acidity measured in %, with the ideal for white wine being somewhere between 0.6 and 0.9%, so 1% is too high.
I have also read of using the Brix:TA ratio as a guide to ripeness. So in the case of the Solaris juice, the ratio is 22.5:1. The ideal range for a table wine is 30:1 – 35:1. Another sign that it is not quite perfect. But as the grapes looked like they were about to go over-ripe (see picture below) I don’t think I could have waited any longer for the acidity to fall.
You can see some of the grapes turning brown. I left one bunch on the vine and only 3 days later they looked like this:
Quite a lot of the grapes were turning brown and starting to rot. So it may just turn out that in the good old English climate the grapes will never really reach full ripness, and that it is just a case of waiting as long as possible, and picking before they go off!
I am now waiting for the Phoenix and Solaris to ripen, as they are next. The SG last measured 1.070 for the Phoenix and 1.075 for the Orion. I haven’t measured the TA as I don’t want to waste any grapes, I’m just going to hold off for as long as I dare.
Here is how the Phoenix are looking now. They have changed colour from green to a yellowy colour and taste good, so they are well on their way to being ripe:
