Harvesting tips

Harvesting can be ‘planned’ or ‘unplanned’. This does not refer to the timing but the quantity of grapes that are removed in a session. It is possible to remove all the grapes at a single session, but this may not be a good strategy for the amateur with limited processing capacity.

The limiting factors are:

  • Destalking or crushing - you need a machine for one or other because uncrushed grapes will not press easily.
  • Press capacity
  • Storage vessel capacity.

Do not pick more fruit in a day than you can process to a point at which it can be left without harm. A useful rule of thumb is that it takes about 2.5lb (1.13kg) of grapes to produce a wine bottle of juice. So plan the amount of grapes that you pick.

If you detect the onset of botrytis, one option is to harvest early. This will generally produce a high acid juice; this can either be deacidified or used for sparkling wine, again Seyval Blanc does well as a sparkling wine.

Sugar and Acidity

Fruit acidity is initially high and falls as the fruit ripens. Sugar levels are substantially attained before the acidity falls so the sugar level is not the best guide of when to harvest although it is the easiest to measure (either with a refractometer or a hydrometer).

To measure the acid levels you need to do some basic chemistry – an acid titration. Acid kits are available from homebrew shops; the cheaper ones supply a small syringe to dispense and measure the standard test solution of sodium hydroxide. More serious testers use a burette for this purpose and if you propose to do much testing it is worth getting a burette as it is possible to use smaller samples - and so perform more tests with the small bottles of standard solution supplied - whilst retaining sufficient accuracy for wine making.

Pips

Pips are probably the amateur’s best guide. They start life green and soft and turn darker and harder - in much the same way as apples. Green pips mean under-ripe fruit. Note that the juice taste is not as good a guide as the pip’s colour and condition. A sweet juice may mask higher acidity; so although it is interesting, taste is not a very dependable guide to a novice.

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