Washing grapes reduces copper but does not affect aromas in the wine

or the 2022 and 2023 vintages in the Rhone Valley, engineers from the French Vine & Wine Institute (IFV) immersed 20-kg cases of Rolle, Sauvignon and Colombard grapes for five minutes in a bin containing 90 litres of water stirred with gas using two sintered stainless steel injectors. For each grape variety they repeated the process until they produced two 100kg batches of washed grapes (Lessrescu project*).

For the Colombard, the washing lowered the copper content by 42% after pressing, and by an extra 45% after settling compared with two unwashed control batches.

After fermentation and bottling, the engineers measured on average twice as many free thiols in the wines made from washed grapes than in the unwashed batches. “This was observed for the free 3SH, which is responsible for grapefruit odours above a perception threshold of 60 ng/litre, and with free 3SHA, responsible for tropical fruit notes above 4 ng/litre”, explains IFV. They did not, however, notice any effects of washing when measuring total thiols. The same was true for analysis of the “fruit menu”, including esters, terpenols, C13 and pyrazine.

In triangular tests conducted in black glasses by 18 panellists, the two wines made from washed grapes were rated as slightly more intense for yellow fruits but only one judged them more intense for citrus fruits and tropical fruits. Overall, the differences in copper concentrations were not perceived in the tasting. This was also true for the Rolle and Sauvignon blanc varieties.

* A project coordinated by IFV in conjunction with Inter-Rhône, VetAgroSup and Dubernet laboratories with financial support from the South Regional Council and Europe between 2022 and 2024.