Treating RO water for sparging

[Woolsocks]

We're installing an RO system to demineralize all our brewing water. We'll be adding salts to the mash to get appropriate pH and ion content, but I'm not sure how to treat sparge water, if at all.

Option A is to sparge with pure RO water, which may be slightly acidic due to carbonic acid.

Option B is to inject a small amount of phosphoric or lactic acid inline to ensure the pH is something like 5.5-5.7.

In either case, lautering will stop if the pH of the runnings rises above 5.8 or the gravity of the runnings drops below 2°P.

Those who use RO water - what do you do?

[Woolsocks]

Yes, I suspected the low alkalinity would mean the buffering capacity of the mash would hold the pH in place during sparging. I guess I'll have to try it out to be sure.

Mineralizing sparge water would be a logistical challenge, so I wasn't going to do it for that reason. I wasn't aware of the osmotic pressure issue though - is there some further reading I could do about that?

I can see some reasons for adding minerals to the kettle, including Ca retention, pH adjustment, and adding ions purely for their flavor impact without changing mash/sparge chemistry. For example, I sometimes add NaCl to the whirlpool just to give a little boost to the sodium content of the wort. Yes, I could do it in the mash, but by waiting until the whirlpool I can get the dose exactly right and not worry about losing ions in the mash.

And I agree that 3°P is a safer place to stop than 2° - 2 would be the absolute lowest I'd go - 3 would make me sleep better.

[TL Services]

Would the answer not be to mineralise/Burtonise the RO product water? Then all your brewing water would be to the same specification.

[Woolsocks]

Yes, except that all my beers call for different mineral profiles!

[dick murton]

Many, if not most of the big breweries using RO, add mineral salts to the mash only, and sparge with pure RO water. It is much the simplest way when brewing a range of different beers. It simply means you have to add slightly more salts at mashing in to get the final mineral composition flavour etc.

Sorry, but I really have no idea what sort of percentage increase is required compared to treating both the mash and sparge water, but I suspect you do not add as much in total. And because I haven't used the freely available water composition calculators to any extent, I can't say how accurate those will be at predicting the final outcome.

[jwalts]

I add sparge water calcium salts to the kettle instead of the sparge water directly for one simple reason: changes in HLT volume - which often happen in the middle of a sparge - make direct water dosing extremely impractical. Luckily, the alkalinity of my water source is low and my late runnings pHs are fine. If that wasn't the case, I'd sell my soul for a cold liquor tank (check out Ale Asylum's setup when you have some free time in Madison).

Joe