Why does mineralization matter for an RO water system for coffee?

[theoldcoffeebrewer]

I have been making my morning pour-over cup of coffee using water purified from a RO system for years now.. Although I see the value in the purification done by an RO system, I am not too certain as to why many are concerned about the lack of "mineralization" aspect (i.e. RO removes all minerals)? Would minerals added back to this pure water positively affect the coffee consistency or taste?

I assume some of you use the RO water as the input water to your coffee machines, hence remineralization is obsolete due to evaporation concerns.

[Nate42]

Adding bicarbonate (sodium or potassium) provides some buffering of the acid in coffee. Some formulations such as rpavlis water stop there. Others add hardness minerals like calcium or magnesium to purportedly improve flavor and extraction. Finally, you want to hit a sweet spot that won't scale but also isn't so pure it's corrosive to a boiler. This last concern doesn't matter for pourover of course.

I'd say if you like your results then it's not broke and you don't need to fix it.

[Dartiguan]

I too have an RO system I have used for years, it is a 5 stage system. The main purpose is to remove chlorine, dissolved solids and fluoride. I am sure it has helped in reducing calcification of the boiler as well, as I have not had any problems in close to 10 years. I have a service due on the system tomorrow and one option I have been offered in the past is to remineralise the water but I am uncertain about the impact of this on my setup. The total dissolved solids in the coffee bean would surely go some way to doing this but I am unsure of the impact as I say. Are there any Home Baristas that can point to articles that might illuminate an answer to this?

[luvmy40]

Another reason for remineralization is that pure water is not conductive and most electronic water level sensors cannot detect it. This, obviously has no bearing on pour over or most emersion brew methods. It can be a huge issue for boiler machines.

[Nate42]

RO water isn't totally pure, what you get depends on the water coming in and the age/quality of the filter. RO water isn't normally so pure that conductivity based level sensors have a problem with it. The potential for a problem there is something to be aware of if your boiler fill sensor seems to be behaving strangely of course. But if everything seems to be working I wouldn't sweat it.

Further on the subject of RO water not being totally pure: this can be a good thing in that hopefully you've got enough buffering capacity that the pH will stay safely 7 or above. If you are going to be filling your boiler with your RO water, you need to verify that the pH isn't acidic to avoid potential for corrosion. Also, you need to purge your boiler periodically to avoid the concentration of residual minerals building up over time.

There's lots of detailed info on water available in the faq section of this site if you want to go into the rabbit hole.

[theoldcoffeebrewer (original poster)]

Interesting points! Is this what most artisan coffee shops do to their water?

[theoldcoffeebrewer (original poster)]

I see - that's why it is suggested to add sodium/potassium for buffering while also adding calcium or magnesium to extract flavors and improve taste, while maintaining the pH above 7 for not scaling boiler.

I'll take a look at the water FAQ

[Dartiguan]

Just had a look at my RO system again after revisiting this thread. I have a TDS meter (Total Dissolved Solids) not too expensive on you know where. My filtered water at the RO tap measures 12ppm, it is the same for the cold filtered water at the fridge line, my cold town water tap measures 100, My hot water from the kitchen tap measures 137 and the hot water from the HX unit in my espresso machine measures the same at 137 after 5 minutes although initially it measured 144ppm when I first put the TDS meter in. Scale in a second hand large SS boiler I guess settling. The point is there is a significant difference in water from a RO system and I also have a remineraliser as a final stage in my system. Hope this might help someone if they are looking for comparisons.