I'm starting to run low on mineral concentrates, so I decided to film myself preparing my next batch of Rao/Perger brew water concentrate. For a very detailed explanation of what all of this is, please read my blog post on water for coffee before you watch this video. There is also a ton of comments with questions and answers that you may find interesting below that blog post; the amount of questions I received is what motivated me to make this video.
I started using the Oxo seasoning squirt bottle because it is incredibly practical for preparing brew water from a concentrate, and it is made of only plastic, which doesn't corrode. Even if the brew water is not corrosive in the end, the concentrate itself is very corrosive before dilution, so I recommend avoiding contact with metal as much as possible; both glass and plastic are fine. I also like the fact that you can pour a bit more precisely with the squirt bottle and it's not perfectly airtight, so your bottle won't explode if your concentrate is still degassing. For more information on preparing the brew water from your concentrate, see this other video I made about that.
The squirt bottle has a capacity of a bit over 350 mL, so I decided to prepare a concentrate of 350 mL with the same concentration as usual, such that you require 4 grams of concentrate per liter of distilled water to prepare your brew water. This requires the following ingredients:
Epsom salt (MgSO4): 8.75 grams
Magnesium chloride hexaxydrate (MgCl2 x 6H2O) : 3.5 grams
Calcium chloride anhydrous (CaCl2): 2.64 grams
Sodium bicarbonate (NaHCO3): 2.98 grams
Potassium bicarbonate (KHCO3): 3.5 grams
Please make sure that all your ingredients are food grade, not lab grade and not pharmaceutical grade. Food grade minerals may be less pure than these other options, but the impurities won't be dangerous for your health. If you use different hydrate forms, please refer to my Google Sheet with all the brew water recipes and select the appropriate weight for your particular hydrate form.
As you can see in the video, I used a milligram precision scale, and I made sure to be within ~0.003 grams of my desired weight for each mineral; I don't believe variations smaller than this will matter in the end because I my manipulations in transferring minerals to the glass container and the squirt bottle are not precise to one milligram.
I used a pyrex measuring cup which I put on my brew scale and tared, then I transferred each dry mineral in the measuring cup. I used a measuring cup because it doesn't corrode and has a pouring beak.
As you can see, I put the buffers last (sodium bicarbonate and potassium bicarbonate) because they tend to be more messy; I should actually have put the sodium bicarbonate last, because it's the worst by far. I had to clean up my equipment before I weighed the potassium bicarbonate because of this, and I made sure to dry it very thoroughly. For sodium bicarbonate, I put a bit more than the required weight (about 2.99 grams but I don't remember how much exactly), but I should have put even more to about 3.0 grams, because there's a good 0.03 grams that sticks to the plastic cup and I needed to get it out into the pyrex measuring cup with my fingers. Notice that I weighed the cup again a few times to see how much was sticking to it, and deduced whether I had put enough in the pyrex measuring cup with a simple subtraction.
Once I had all the minerals in, I poured boiling distilled water in the pyrex cup until I had 350 grams total. I tared the pyrex before starting to put dry minerals in, so that 350 grams counted both the minerals and the distilled water. Using boiling water really accelerates the degassing phase, most of which is gonna happen within the hour rather than over more than a day. I have not seen any effect whatsoever on taste, measured hardness, total alkalinity or the look of the resulting brew water since I started using boiling water. I used a glass stick to mix it up; the one that came with the Melodrip came in handy here. As you can see, the concentrate looks white, precipitates and sediments very quickly. When you mix it back up it becomes milky white again. I wanted to make sure I wouldn't go over 350 grams, so I put the last 5 grams of distilled water with a glass pipette instead of pouring it directly with the kettle.
The drawback of using boiling water is that I need to let it cool before putting it in the squirt bottle; it might be food-grade plastic, but I don't think it's made to hold boiling water. And at that point I realized that the pyrex measuring cup was a poor choice to let the concentrate rest, because I can't put a lid on it to avoid heavy evaporation (which would then change the concentration of my solution). Therefore I decided to transfer it to a glass mason jar and put just the central part of the lid on, for a bit less than an hour. It's made of metal, but it didn't have time to corrode, an it only ever touched water evaporating from the concentrate (therefore free of minerals). This is a phase where a lot of CO2 is degassing quickly, even if you use boiling water, so it's important not to screw a lid tightly on the jar. You'll notice that, when I transferred the concentrate, some deposits remained in the measuring cup. To get it back in the mason jar, I poured back some of the upper layer (clearer) water into the measuring cup, spun it around to gather in all deposit, then poured it back again. You can do this a few times until there's no more deposit.
I let the concentrate cool in the mason jar for 40 minutes, when it felt just warm to the touch instead of hot, and then I poured it into the squirt bottle with a plastic funnel. I used the back-and-forth trick again to get all of the deposit transferred. I didn't screw the squirt bottle all the way back just to be entirely sure it doesn't explode (I'll do that tomorrow), and I placed it in the fridge.
Make sure you clean everything that touched the concentrate with a bit of vinegar, then warm water and soap (or the dishwasher). This will remove any deposit and keep everything clean.