At the distillery in Wales, we used deionized water to dilute or cut back the gin. Many people have asked why we use deionized water instead of reverse osmosis (RO) water for alcohol dilution. Let’s take a look at how RO water and deionized water differ.
Reverse Osmosis Water
RO water has gone through a reverse osmosis filtration system, so we need to first understand what osmosis is. Let’s say we have a glass of water that is divided by a semipermeable membrane. It’s semi-permeable meaning that some things can pass through the membrane while other things cannot. On one side we dissolve 10 tablespoons of salt, and on the other side, we dissolve 1 tablespoon of salt. Osmosis is defined as a process by which molecules of a solvent (Ex. water) tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one. In this case, water will move from the side with 1 tablespoon of salt to the side with 10 tablespoons of salt.
Reverse osmosis is the opposite of osmosis, so we change the direction of the solvent, water, through the semipermeable membrane. Instead, the water moves from the side with 10 tablespoons of salt, which has a higher concentration, to the side with 1 tablespoon of salt, which is lower in concentration. This is what is happening in the reverse osmosis filtration system. However, instead of salt being dissolved in the water it is contaminants dissolved in the water. The side with a higher concentration of contaminants is left behind on one side and can be disposed of. RO water systems are quite affordable and remove 90-99% of contaminants in water.
Deionised Water
At the distillery we used deionised water. The water was delivered to us in 1000L intermediate bulk containers (IBC) that look like this:
Deionised water is water which has had ions such as calcium, chloride and sodium ions removed through an ion exchange process. This means the water has no charge and will not react with electricity.
Deionised water can be purchased in various grades of purity. I did some research online to see how high grade deionised water is produced, and it turns out that high grade deionised water has gone through more pre-treatment processes before actually getting deionised. One of these pre-treatments is usually the RO filtration system which removes the majority of contaminants from the water. Only the smallest particles are left for the deionization filter to remove. This means that a high grade of deionised water is more pure than RO water, since it has undergone reverse osmosis filtration prior to being deionised.
So which type of water is best for alcohol dilution?
Deionised water has to be used immediately. Once deionised water is exposed to air it starts to react with the carbon dioxide in the air and degrade. This causes it to have an electrical charge again. At the distillery, we used deionised water, and it usually sat outside in an IBC for about 3 weeks. When I needed it I opened up the top, dropped in a hose, and pumped it into a different container. It is safe to say that our deionised water was regularly exposed to air which meant it was no longer deionised. Additionally, rainwater entered the IBC overtime as well.
With that in mind, RO water is better for general distillery usage since it is cheaper and removes a broad spectrum of contaminants and dissolved solids. The RO filtration removes 90-99% of the contaminants in water. If you use RO water for alcohol dilution you can be confident that the water is high in purity.
DI water has the potential to be purer than RO water, but any benefit is lost if the water is not used immediately. If you have to pick one type of water to use, choose RO water since it has 90-99 % of contaminants removed.
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