Someone asked about this recently, so I took another measurement... Update for pH of standard Starsan solution made with distilled water... 2-20-2010: <2.8 < many measurements omitted for brevity> 4-23-2013: <2.8, No noticeable change in clarity So now we're at more than 3 years with no change (that I can identify) to the pH and clarity of my test batch of distilled water starsan solution.
I wasn't expecting anything. But the claims of 'the pH will never change' struck me as odd, since nobody had ever tried it to my knowledge.
Acids don't break down over time, and the only way the pH would change is if the solution was reacting with the container or was left open and some sort of water evaporation occurred. If you buy a jug of white vinegar tomorrow, it'll still be white vinegar with the same pH in 30 years. Same applies to Starsan, which is essentially a combination of phosphoric acid and another type of acid/surfactant. Probably could've saved yourself a 3 year experiment by using the Google or asking one of the many chemistry-educated peeps on BA.
good to know someone's tried it. I shall get some distilled water before making another solution of spray-starsan. Usually I mix a fresh batch tho. It's cheep and does a good job.
I don't know the full ingredient list (trade secret stuff) but I know it contains dodecylbenzene sulfonic acid. It's used to make detergents and more common in its salt form, which is a surfactant. I'm assuming that's what provides some of the surfactant qualities. http://www.midwestsupplies.com/media/downloads/310/Star San MSDS Sheet.pdf Either way, it's good to note that acidic solutions in sealed containers usually don't change pH over time. For example, when I worked in the lab, we used various acids that were many years old and they still retained the same pH as when new. Nice to know your Starsan jug won't expire (unless you leave the top open!)
So how would anyone know what the unknown components, diluted in water, in a milk jug, sitting on a kitchen counter with partial sunlight, do to the pH of the solution over time, without trying it? It's potentially more complicated than the question of whether acids break down over time.
Basic chemistry. Acid/base reactions aren't slow. If there was something in the Starsan solution that could affect the pH over time, it would occur rather quickly. Especially in a solution that's 65% acid. Adding water would affect the pH initially, but that won't change over time either. Sunlight has no effect on pH. The only thing that could affect the solution over time would be the milk jug. So it's definitely good that you discovered milk jugs don't break down upon prolonged contact with Starsan.
If you mean directly, I agree. But UV can certainly participate in chemical reactions. Yeah. That was kind of the point. People had been talking about the fact that they were mixing up gallon batches of solution, re-filling their spray bottles from the gallon jug, and basically making a single batch last a very long time. But nobody could say definitively if there would be changes.
I'm a big fan of the scientific method myself. "Testing the hypothesis" is always in every version of it I have ever known.
Keep giving it funny looks and more time. It's sure to go up. Thanks for checking it again. For me, I think a three year shelf life will prove sufficient for my brewing needs.
I greatly appreciate this "experiment", maybe the chemists already knew the results, but the real world test is valuable in my opinion. It certainly makes me feel better about mixing up a batch and letting it sit in my garage for 6 months while I slowly use it up. thanks for the effort Vikeman
So I would like to ask you what happens with buffer 4 and buffer 7 I use to calibrate my Phmeter, they are in lided jars very well closed but I have used them 2 times ,they are 2 years old.I have read they should not be older than 6 months,is it true?
This is the vendor recommendation for shelf life of calibration buffers, although I don't know how fast they drift/degrade past the shelf life. In general, you don't want to mess around with instruments used for calibration - although, in a homebrew setting, you probably have a bit more leeway than, say, a pharmaceutcal company.
Buffer solutions expire over time when they are used. They either become contaminated, or trace CO2 enters the container and forms carboxylic acid in the buffer solution. An unused buffer solution in a sealed container should not expire. The expiration date exists because manufacturers do limited stability testing and likely want to sell you more product. Back when I worked in a lab, I found a buffer calibration kit for our pH meter in the back of a cabinet. It was long past expiration (3+ years) but unopened. I tested it against a brand new buffer kit and the pH values were spot-on. One thing to keep in mind is that buffer solution pH doesn't change appreciably when water is added. You can buy a brand new set of buffers and dilute them with distilled or RO water and create multiple aliquots to be used over time.
Two completely nitpicky/pedantic comments (Chemist/Biochemist)... CO2 enters the system and can produce carbonic acid (carboxylic is the generic group name for organic acids, and denotes R-COOH or R -CO2H in organic chemistry; Carbonic acid is H2CO3, bicarbonate is HCO3-, carbonate is CO3 2-). Several commonly used lab buffers do undergo appreciable pH shifts upon dilution and temperature. Tris is such a buffer where its pKa of 8.06 shifts approximately 0.03 units/degree C rise in temp, which can lead to dramatic pH shifts when solution temperature changes (e.g. pH 7.0 Tris at 4 C will go to a pH of 5.95 at 37 C). Similarly its pKa will actually shift with dilution, dropping 0.1 pH unit per tenfold diltuion. All points regarding buffers assume the solution is in the working range of the buffering capacity of the buffer in question (pKa +/- 1 pH unit).
