Why do SodaStream plastic bottles 'expire' after three years?

For Sodastream (make your own carbonated water at home system), the plastic bottles have a three year life span, they say “do not use after [the date]”.

Is that because possibly the gasket on them will have worn out, so it will lose carbonation?

Or is it because the plastic they use will leach horrible chemicals into the water?

I didn’t know plastic would expire so quickly.

Unless it’s a perishable like meat or milk, usually expiration dates don’t mean that they go bad after that date. They mean that they have only been tested out to that date. Beyond that, there is no test data so, according to government rules, they can’t say things will be fine with certainty.

I went looking to see how much pressure a sodastream co2 tank provided, and found this:

You’ll notice that the bottles are shaped like pressure canisters… because they are. Polypropylene is durable but not eternal (link to vaguely-related article). The manufacturer wants to prevent any weakened bottles from being used. Or, more probably, wants to cover its rear against liability in bursting-bottle accidents.

Also, there’s money to be made selling replacement bottles.

What Heracles said. Mine are now eight years old.

I used to reuse soda bottles when I homebrewed beer. Occasionally, esp in hot weather, they would burst from the pressure. I still have the stains on the ceiling from one such explosion.

That is because the are safety factors and conservative assumptions built into that lifespan to ensure that even if you moderately abuse the bottles (e.g. washing in hot water and detergent, exposing to sunlight or high heat, et cetera) they will still have integrity. Fortunately, a polypropylene bottle containing 30-40 psi of water and dissociated CO[sub]2[/sub] is unlikely to present a substantial harm even if it does rupture and with the thickness of the SodaStream bottles, I would expect that they could probably retain >200 psi in the new condition. (A much thinner wall standard 2 litre bottle can retain about 100 psi pressure in new condition.)

The answer is that you can probably get away with using these bottles indefinitely as long as you do not abuse them or subject them to accelerated wear conditions, and if they do fail, they’re unlikely to pose the kind of hazard that high pressure (3000 psi) air or volatile gas would. SodaStream is essentially covering themselves against a frivilous damage suit in case a bottle does rupture and spook some clueless moron. But with real pressure vessels, they are periodically proof loaded and inspected to ensure integrity, and correct process is to scrap them if they show significant wear, damage, or defect.