Question:
Just wondering if anyone uses reverse osmosis water for espresso. I ampulling shots using a Rocky, PID Silvia with commercial PF and 'LM'double/triple baskets. I've was consistently getting very good results withdistilled water but installed a reverse osmosis (RO) system last year andswitched over to RO water. Since then I was never able to get a good shot.Extraction time, texture, color and crema were all bang on but no matter howI tweaked the PID, changed my grind/tamp and tried various beans (many ofwhich I earlier considered to be 'tried and true') I always got sour shots.Really sour in that it was never drinkable straight up and at best wasmildly noticeable in a latte. I was very reluctant to think it was the waterbecause it tasted great from the tap and I tested it to have negligibly lowmineral content. I thoroughly cleaned and backflushed the machine but thesourness persisted. Hot water run through the portafilter with no coffeetasted fine, with no odour or sourness... it just makes sour coffee!

Does anyone have similar experiences or have an explanation for this? Irecall reading somewhere that reverse osmosis water is not totallypH-neutral - could that be affecting the taste of the coffee? Right now I amback to distilled water and everything was as it used to be. The sournesstotally went away the moment I put in distilled water, and I am now backwhere I started - great coffee, but breaking my back hauling around those18L water bottles.

Answer: RO water by itself isn't very good for coffee; neither, by the way, isdistilled. The easiest solution for an RO system is to put an inlinecalcite filter after it to add back a couple of grains of hardness. Ithink Chris Coffee sells one that goes into a housing, and OmnipureK5648 is a fairly widely available 10" inline one.

There's a lot of interesting chemistry going on in a cup whileit's brewing. Minerals don't just add flavor by themselves. They bondwith important flavor elements in the coffee grounds. Assuming you'restarting with good beans, without minerals, you are leaving lots ofgood flavor behind. A blind comparison of coffees brewed with water atdifferent mineral levels is pretty persuasive for most people. Reamshave been on the subject.