Reverse Osmosis

Osmosis is the spontaneous flow of water through a semipermeable membrane, when the solutions on both sides of the membrane have different concentrations. The water flows from the less concentrated side to the solution with the higher concentration. Thereby, a pressure difference is caused, which is called the osmotic pressure.

Can it be made so that the water also flows in the other direction?

The process described above can be reversed when an external pressure is applied to the more concentrated solution. This pressure has to be higher than the osmotic pressure of the solution. Now the water flows from the side with the high pressure to the side of the low pressure. The substances dissolved in the water are not able to pass through the semipermeable membrane, though, and therefore remain on the left side. On the left side, the dissolved substances are enriched, and on the right side, pure water is obtained.

This process is called reverse osmosis.

Where Is Reverse Osmosis Applied?

A very important field is the purification of water. By means of reverse osmosis, dissolved substances (salts, contaminants like heavy metals or pesticides, bacteria, viruses..) can be removed from the water as in an extremely fine filtration. This relatively new technology is very economic and environmentally friendly in comparison to other methods like distillation, for example.

Reverse osmosis is used for the desalination of seawater, for the technical production of very pure water and in plants for water treatment in households.

And what has wine to do with reverse osmosis?

Not only the purifying effect, but also the enrichment on the other side of the membrane is utilised:

Instead of the conventional sugaring during the production of red wine, the must can also be concentrated with reverse osmosis to increase the sugar content and intensify the colour. In the beverage industry, reverse osmosis is used in the same way to concentrate fruit and vegetable juices.