Definition: Wood moisture content in cooperage

In cooperage, the amount of water contained in wood, expressed as a percentage of its dry mass. Example: H 18%.

For wood, we generally refer to the moisture content as H %, known as dry moisture (relative to anhydrous wood). It is calculated as follows: H % = ((Wet mass minus Anhydrous mass) divided by Anhydrous mass) x 100. In other words: H % = (Mass of pure water/Dry matter) x 100. The moisture content varies from 50 to 120% (or more) for saturated wood (green wood), from 10 to 20% for air-dried wood (drying takes approx. 1 year/cm of board thickness), and 10% and less for artificially dried wood (mainly using hot air conditioning, heat pumps or vacuum drying - drying time between 1 and 3 weeks). There are three types of water in wood:

-Free water is the water present in green wood. Figuratively speaking, it is the water that comes out of a sponge when you squeeze it. When this water is removed, the wood does not shrink.

-Bound water is the water that is part of the fibre composition. In the case of our sponge, this is the water contained between the fibres of the material but which we cannot squeeze out. This is the water that is removed between 30% and 0% humidity.

- Constitutional water is water that is part of the chemical composition of wood molecules. Its removal leads to the destruction of the wood (by fire, for example).

In cultivation, during intense heat, transpiration from the foliage can create a particularly humid area inside very dense canopies. Even minimal differences in humidity can play a role in the development of botrytis.