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Reverse Osmosis

James_Hoffmann_21713

In my job I end up using reverse osmosis units quite a lot to treat water, to reduce both its hardness and its total mineral content.

I keep reading about other applications for reverse osmosis, and wonder whether there is an opportunity to get some interesting cooking results from abusing a small domestic unit.

I had read about various industries using them as a way to standardise concentrations - for example, pushing water out of milk until the protein level (as a percentage) is what it needs to be.

I know rotovaps are a potential way of concentrating liquids, without damaging them excessively through heat. They're also ludicrously expensive.

A domestic RO unit can be picked up from under $200. I have no idea what would happen if you pumped a well strained soup through one, but I suspect you'd be able to massively concentrate and intensify it. Alternatively any kind of maceration or infusion (thinking about cocktails here) could be reduced without the use of heat. Cleaning the membrane afterwards might be a complete nightmare, and keeping it sanitary may also be an issue (there are RO cleaning kits out there....)

Just an idea that popped into my head - wondered if anyone else here had thought about this stuff, or even played with it a little?

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Comments

Chris_Young_80640

So, in general you wan't something like a cellulose filter. Broadly speaking, there are two kinds of filters. Membrane-style and depth-style. Membrane-style are like sieves, a flat surface with holes or pores of a very specific size. Depth-style filters are somewhat thick and tend to hold back particles above a specific size because the path length through the filter is too tortuous for them to make it through, although the actual pore sizes might actually be larger than the particles.

Depth-style filters are far more resistant to fouling than membrane filters. Basically, as soon as the surface of a membrane filter is coated with a plaque, it's done. Depth filters can cake up quite a bit before there is no longer a path through the filter.

A good, inexpensive filter to put upstream of an RO filter would be a hobby-style wine filter. Or, you can centrifuge the liquid first to remove the large solids.

James_Hoffmann_21713

I guess it would probably be worth running everything through a pretty fine sieve - something like 50 microns maybe? Or smaller?

Chris_Young_80640

I think the biggest challenge will be prefiltering to avoid fouling the RO filter. I've done micro filtration in the past and it was critical to use a series of filters to avoid clogging the whole thing up. I'm traveling right now, but I have a book on RO concentration for the food industry at home. Will post some details next week.

Tim_Sutherland_52834

With the home units is it possible to stop the process once it starts. As I see the home units are designed to produce clear drinking water from a storage tank. The storage tank is fed water from the RO filtration unit. If I have 1 litre of liquid I want to concentrate do I just have the unit on for a few seconds, taste the liquid and continue until I get the taste I am after?

James_Hoffmann_21713

I think it would make a poor filter, as the only thing passion through the filtration membrane is water (not technically true but close enough to make the point). I can only see concentration applications working.

Additionally I forgot to mention that membranes have a bell curve of efficiency and pressure, o you'd need a pump to get the incoming liquid up to 5-6 bars (72-87 psi)

Tim_Sutherland_52834

It sounds like a good idea, and at $200 it one of the cheaper kitchen toys out there. I haven't heard of anyone trying it at the "home" level.

I could see it being used two ways, one concentrating heat sensitive liquids and two filtering liquids.

I would see issues with trying to RO anything that had large partials in it. You would have to start with a consomme. Find the "right" size filter may also be an issue. If the filter can remove chlorine, I assume it is also removing the "taste" from the liquid.