The Grape Harvest

Are the grapes ripe?

Autumn is closing in and your precious crop is hanging there, do you pick or leave a little longer, what’s the weather going to do?. The first thing to do is test the sugar content of the grapes. There are two methods, either use a hydrometer which will require at least 150mls of juice or a refractometer which needs one grape!. looks like an obvious choice but refractometers are the expensive option. We use a refractometer because you are able to test several grapes around the vineyard to get a mean value. The readings are accurate and instant.

Using a Refractometer

Most wine making books will contain a table showing the specific gravity of the juice. This can be used to understand the amount of sugar you grapes contain and the potential alcohol it would produce when fermented. For an English wine I would suggest a maximum of 11% alcohol, or more preferably 10%. If you look at the refractometer reading above, you will see that the reading is 73°o. this would produce a wine with about 9.8% alcohol. So the view at the time of testing would be to leave the grapes a little longer and probably test again in two weeks time.

There are some factors to consider away from the sugar content, this is the total acid levels. Grapes developed for wine making differ from those designed for eating. Eating or dessert grapes have low levels of acid and although the sugar content is not particularly high they will taste sweet. A wine grape of a similar sugar content would taste sharp like an apple because of its higher acid levels. These acids are vital to ensure your wine has a ‘backbone’ and will have a reasonable drinkable life span. An English wine can develop for several years in the bottle, generally 2-3. Our wines are at their best after a year in a carboy, then bottled for another year, and should not decline for a further 2 years. Wines in Bulk or in bottles are best kept at 12 – 14°c.

The table below shows the optimum periods for picking in relation to sugar and acid levels. It will only be experience of the varieties you grow to know what levels of sugar are achievable and the acid levels which remain.

Acid sugar change during ripening


Preparation is the key to success before you start picking, consider the following;

  • what are you putting the grapes in  – plastic boxes are best with no holes in the bottom
  • how are you cutting the bunches off – snips or scissors are best. Don’t use secateurs fingers get in the way!
  • The weight of the crop – only pick as much as you can deal with in one go
  • how are you going to crush the grapes  – a mill is quickest.
  • how are you going to press the grapes – a picture of our press on the right (home-made)
  • what containers is the juice going into – always have spares
  • has the equipment been cleaned – rinse thoroughly
  • have you got enough yeast and pectic enzyme
  • where will the juice be when fermenting – have you got a stable temperature environment – in the right range for the yeast
  • Don’t pick wet grapes! it will dilute the juice and the sugars

OK, get the harvest in!

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