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I intend on making caffeinated water for personal consumption, in batches large enough that it will take several months to consume them, using containers which are not hermetically sealed, and for which it is not practicable to refrigerate. What would my options be as far as preservatives?

Commercial caffeinated water products i've bought use sodium benzoate, but I can't seem to find information on how much to use. I am also interested in the possibility of using citric acid, but again i'm not sure what pH level I would be looking for. If it matters I do have a lab grade balance (Sartorius Entris 64-1S) which would be capable of measuring sub-milligram amounts and a dispenser to match.

  • Might be better asked on chemistry.se? – Erica Jun 4 at 0:04
  • Why? This sounds like a perfect setup for problems. I wouldn't drink plain water that had been sitting in an open container for months. – George M Jun 6 at 23:17
  • Did you read the question? The entire purpose of the question is how to preserve it, not just leave untreated water in a opened container for months. There are numerous commercial concentrated caffeinated water products. I just cant find any info on the concentration of sodium benzoate the one I have uses, and nothing from the FDA beyond that it shouldnt exceed 0.1% accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/… – Matt Jun 7 at 18:58
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    If the containers are transparent you might consider letting them sit in the sun. This is not perfect, but it would help with keeping it sterile. – user1721135 Jun 7 at 20:41
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    @user1721135 No, otherwise you wouldn't see algae growing in the outdoors, where there is nothing to filter it out. Many plastics are fairly good at filtering out UV anyway, though it depends entirely on the wavelength and the plastic type. – bob1 Jun 10 at 9:43
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It seems to me that the risk of adding soduim benzoate, while small, is higher than adding no preservative at all. I doubt you really need any type of preservative. If you begin with impeccably clean bottles...perhaps sanitized the way a home brewer might sanitize beer bottles (using iodine or other sanitizing product), and work cleanly, I don't see a safety risk here. Use a known clean water source. You could also decrease your worries further by using distilled water, but the taste might not be agreeable. It seems like the biggest potential problem is that you might grow some algae.

Now, I don't quite understand your comment above where you state that a 16oz container would contain a hundred or so servings. If you intend on taking a swig, and re-capping the bottle...well, every time you do that you introduce bacteria into the equation. Additional potential problems arise if you were sharing that bottle with others. This, of course, could be remedied by pouring your dose into a cup.

  • Regarding your first link, I'm aware of the risk and since this doesn't contain vitamin C, i shouldn't really need to worry about it. Regarding the second link and the rest of the paragraph, those are single use sealed containers, the exact opposite of what I intend on doing. Regarding your second paragraph, the containers would be something like amazon.com/Quik-Shot-Plastic-Built-Chamber/dp/B00RM5FI5I And I am aware of the risk of introducing bacteria/mold/viruses by opening the bottle, which is what this question is about, how to prevent this by using chemical preservatives. – Matt Jun 9 at 17:04
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    Short answer: you can't realistically maintain sterility with repeated openings. You could learn sterile technique from a microbiology course, but this won't help if you are physically touching the opening. I work in a micro-lab and we use very expensive laminar flow hoods and sterile equipment to maintain sterility of solutions, and these still don't work if you have bad sterile technique. – bob1 Jun 10 at 9:50
  • If you go to any supermarket you can find countless products which are designed to not be refrigerated, to be opened numerous times, and have a usable life measured in months after opening. They all use preservatives to do so, which is what this question is about, but specifically in the context of something which is mostly water. – Matt Jun 11 at 13:03
  • @Matt my main point is that water does not need preservatives to be shelf stable for months. You do, however, need to take care not to contaminate it, or the container it is in, as you consume it. This would be true even with beverages that necessitate preservatives for shelf stability. – moscafj Jun 11 at 13:28

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