Reverse Osmosis Systems

A friend of mine has a salt water aquarium. When he compensates for evaporation, he adds water from a small reverse osmosis filtration system that appears to be of the type that is typically mounted under a sink. He claims that he could not use that water for brewing (even though it is not attached to the aquarium, he just uses it to add water to the aquarium). This sounds fishy to me (pardon the pun). Is there really any difference???

It is the same system. That water can be used.

Thanks Martin!

I think what your friend is telling you is that the RO water could not be used for brewing without the addition of some minerals. While it is in fact true that beer can be made with distilled water (the extract level that home brewers use as the reference for 100% extraction is from a Congress mash which is a distilled water mash) in fact some mineral content is desirable. It doesn't have to be much - the best beers are made with low mineral content water, but at least some chloride is necessary to support a decent level of mouthfeel. Without this the beer can be quite drinkable and even good but it will seem 'thin'.

ajdelange said:

I think what your friend is telling you is that the RO water could not be used for brewing without the addition of some minerals. While it is in fact true that beer can be made with distilled water (the extract level that home brewers use as the reference for 100% extraction is from a Congress mash which is a distilled water mash) in fact some mineral content is desirable. It doesn't have to be much - the best beers are made with low mineral content water, but at least some chloride is necessary to support a decent level of mouthfeel. Without this the beer can be quite drinkable and even good but it will seem 'thin'.

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Ordinarily I would agree with you, but he isn't that technical with brewing and doesn't know about the usage of mineral additions. I tried explaining water adjustments to him one time and he was interested in the concept but not in the science (he's a retired police officer)... I'm guessing that his aquarium guy said something about the water one time and he just confused it.

What does DI stand for? My friend and I were talking again last night. As I suspected, his aquarium tech told him it was unsafe. The reason given was "it (the RO) strips everything from the water. I explained to him that is like distilled water. It doesn't contribute any minerals to your diet, but it doesn't hurt you. So we decided we are going to make a Maibock. We will both use the exact same recipe, but one of us will use tap water and one will use "built" water using the RO and Bru'N water calculated additions.

EDIT: And to make things as even as possible, we will likely use one combined starter and ferment them in the same ferementation chamber, as well as keg and lager them in the same chamber.

BigB said:

What does DI stand for?

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I'm not sure if that's a rhetorical question but in any case the answer is 'de ionized' i.e. it is, even more so than distilled, free of any ions other than H+ and OH- both present in very small quantities. As such it is quite agressive i.e. it will corrode metal fairly rapidly (which means months) and that is why it is plumbed with plastic pipe or tubing. But it is quite harmless as is RO water which contains orders of magnitude more ions including those of metals, chloride sulfate but still at low enough levels that we can consider it ion free in planning brewing salt additions.

ajdelange said:

I'm not sure if that's a rhetorical question but in any case the answer is 'de ionized'

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Nope, I didn't know what DI stood for. Thanks!

BigB said:

A friend of mine has a salt water aquarium. ..... He claims that he could not use that water for brewing

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I wouldn't use aquarium water for brewing, either.