Home Carbonation for Magnesium Water

Edition: 2018-10-06
Note: although this basenote is publicly-visible, some links and responses may be IC members-only.

Elements Required

Suitable Water
You must have a source of suitable water for this gambit. Unfiltered public water in most places is unsuitable. Unfiltered well water is often unsuitable. If you are already buying drinking water (purified or spring), it will usually be suitable. Distilled water would work.

In the specific described process, the home already had a reverse osmosis system for drinking water.

Plain Milk of Magnesia
If you’ve already been making Mg-water, you have this under control. If not, obtaining a MoM that is just filtered water and magnesium hydroxide could be more trouble than you suspect. The Mg QICk Reference article would be a source of tips on this.

Home Carbonator
There are many brands and products on the market. For this article, a sodastream® FIZZI™ was used (merely because it, along with a spare CO₂ cylinder and 2 spare bottles, were stumbled upon at a decent price in a regional retail store). Selection criteria to apply are:

• Are the containers air-tight when mated to the carbonator? Having a self-sealing cap would be a plus, but is not strictly necessary. See Step 8 for more info.
   
• Does a local supply chain exist for exchanging or refilling the CO₂ cylinders? In the case of the sodastream® brand, cylinder exchanges are widely available at about US$16.00. Failing that, you’d need some way to refill them ad-hoc.
   
• Are spare containers available? Sodastream® bottles expire. For two people, having three 1 liter bottles is working well.
   
• Economics: include the up-front one-time expense, periodic bottle replacement, and the on-going CO₂ expense. Expect it to be break-even or slightly cheaper than bottled seltzer water, but much more convenient, and providing nearly complete quality control.
   
• Support Life: apart from the refill issue, brands have come and gone. If the home carbonation fad fades (again), they might all disappear. Check brand history, and user reviews.

The CO₂ cylinders are generally at least "ORM-D" for shipping purposes, if not actual hazmats. Delivery to AK, HI (and islands generally) is either going to be expensive or slow (surface vessel).

If the carbonator includes a cylinder, is it full-size, or just a (non-refillable) very low capacity "starter"?

Brand Note:
This article is not an endorsement of the specific brand and product model used. Sodastream® is a very annoying brand, generally. The various models are confusing to compare. The documentation is unsurprisingly heavy on safety warnings, heavy on strident legal claims that may be unenforceable, and very weak on key details of use, with nothing on theory of operation. Such as they are, you may not even be able to find downloadable manuals in your region.

With the sodastream® brand, some machines accept an optional glass bottle (carafe). The normal bottles appear to be heavy duty PETE /1\. Sodastream® claims BPA-free, no phthalates, no PCBs, and no polycarbonate, but says nothing on BPS.

Wider Context Note:
Carbonated beverages are in general discouraged in the Undoctored and Wheat Belly programs, due to pH. In the present reaction, pH is neutralized. But the point here is to expect to have no other use for one of these appliances.

Steps Used by Author

The problem that the machine maker wants to avoid is a vigorous reaction when the CO₂ is injected, typically resulting in a major mess when the bottle is decoupled. In more egregious cases, the bottle could actually rupture. Note from that video that the system is clearly airtight until the bottle is decoupled.

The Mg(OH)₂ + 2 CO₂ → Mg(HCO₃)₂ reaction is not energetic. Indeed, it appears to be a negative pressure reaction. In any event, we allow it time to progress prior to decouple.

Set the machine up as per manufacturer instructions. You’ll probably want to wash the bottles.

1. Fill the carbonating bottle with suitable water, about half full. (We use pre-chilled water, and so skip step 5.)
    
2. Add the recipe amount of MoM. For one liter, that would be 22.75 mL.
    
3. Shake the bottle.
    
4. Add more water to the recommended fill line. For our machine, this seems to be somewhere between the ~~~~~~ fill line printed on the bottle, and the molded ridge line just above it.
    
5. Unless pre-chilled water was used, put the bottle in the refrigerator for several hours, but do not freeze. The lower the temperature of the liquid water, the more CO₂ it accepts, and the less lost at decouple.
    
6. Shake the chilled bottle, and couple it to the carbonator.
    
7. Operate the carbonator for a standard charge or slightly higher charge. For our machine, 3 full presses is standard, and that appears to be sufficient to react all the MoM, and not result in much residual carbonation.
    
8. Leave the bottle coupled to the machine for at least 20 minutes. This allows time for the CO₂ to react. If you decouple early, you’re apt to lose a lot of CO₂.
    
9. If the reaction has gone as planned, what was white cloudy water is now clear, with no obvious precipitate at bottle bottom.
    
10. Decouple. Cap. Shake. Ideally store in fridge. If you lay the bottle on its side, you can more easily check for sediment or precipitate as you dial in the process.
     
11. Once it’s clear that all the MoM was reacted, the bottle can be left out at room temperature. If you get a pronounced hiss on first opening, that may be ambiguous — is CO₂ coming out, or, and perhaps more likely, is air going in.

Serving

When we decant the Mg-water for consumption, we take that opportunity to add some ancient subterranean mined salt (presently 3 cranks of coarse Redmond Real Salt®)

Adding salt at this point provides a generous amount of nucleation sites to release most of the remaining unreacted CO₂.

CO₂ Refills

Gaming the sodastream® refill model seems to be a popular pastime. Personally, I find the US$16 cylinder exchange price to be acceptable, and we have an outlet in a nearby town that we frequently visit. You might not have that convenience.

I have not looked into fitting specifications, nor refill pressures, but those would be essential matters if local refill is the only recourse. If there are fountain pops available in your area, there has to be a supply chain for food-grade CO₂.

The “food grade” bit is important. Industrial and recreational (paint ball) CO₂ may have insufficient purity, or even have deliberate additives (such as lubricants), so do your homework before passing gas.
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Bob Niland [⎆disclosures] [⎆topics] [⎆abbreviations]