Normally, I’d be happy with a water TDS reading like this. I’m not right now. Why? Because it’s the water at home, and one week ago, it was 40ppm TDS, which is 100ppm less exactly one week ago.
About 140 ppm (parts per million) TDS is, according to all the relevant literature, about ideal for brewing coffee. With our the ~40ppm water (we live 30 minutes south of San Francisco), I’ve dialed in my coffee brewing to fantastic flavor. Juicy acidity, sweet, balanced, fantastic. 40ppm is supposed to be a bit low, but it’s been great.
I made coffee on the morning of January 1st. It was (again) juicy, bright, and sweet. I made coffee that same evening for a couple friends. The coffee tasted embarassingly flat, and while it had most of the sweetness, it was missing the juicy-acidity, like as if the tweeters on my audio speakers suddenly cut out. (Perhaps) needless to say, my technique is very dialed-in with my home-lab setup.
My mind raced through all of the variables. I’d been brewing with lower water temperatures lately… maybe I needed to pump things up to higher temps? Tried that… no dice. The grinder is fine. It was the SAME coffee… could it change SO much in 8 hours? No way. So what could change all-of-a-sudden like that?
I had lent my Myron-L water conductivity meter (pictured) to a friend, but I got it back from her yesterday because I had to assume something had changed with the water coming out of our taps. Sure enough, it was 100 ppm higher than my last measurement.
Still… if 140 ppm is ideal, why can’t I get (any of) these coffees as delicious as I know they can be? Perhaps the nature of the 100 ppm could reveal some clues? I mean, if that +100 ppm (or mg/L if you wanna get more nerdy) of impurities are made up of more neutralizing or buffering compounds, it would make some sense. I’ll be doing some more testing. Stay tuned!