PET bottles

[Dr. Dextrin]

If I bought some fizzy water and then used the PET bottles to bottle my beer, how long would it keep before the oxygen got in and ruined it?

I'd keep it in the dark, obviously.

[wetdog]

If they're screwed on properly theres no reason why any oxygen would get in. the C02 produced by the secondary fermentation will keep the beer in good condition as well

[sparky Paul]

Generally speaking, around 3 months is the maximum recommended, due to the slight gas permeability of the PET. However, I have kept beer in PETs for well over a year without any ill effects... and the beer just gets better and better.

Clear PETs must be kept in darkness though, as you say.

[boingy]

In general, I'd be comfortable with about 6 months although it will vary with beer style and bottle brand/design.
If you manage to keep anything you have brewed longer than 6 months you are doing better than me!

[Capper20]

I did some cider many years ago and one bottle got forgotten about for about 18 months, it tasted fine. I've just bottled a couple of 1L PET bottles up as a backup due to not having enough glass bottles spare. We'll see.

[Dr. Dextrin]

Thanks everyone. I've been reading Graham Wheeler's BYOBRA and he seems not to like PET bottles at all - claiming they can lose 15% carbonation in 4 weeks. By that reckoning a fizzy drink would be pretty flat in a year, even before you consider the oxidation.

However, I have to say, that's not my experience with fizzy drinks at all (and the "best before" dates seem reasonably optimistic too). So I thought it was worth asking what others have found. There's a lot of myth in home brewing and it's always helpful to have some facts.

From the replies, it looks like I might get 6 months at least, assuming I can get some decent quality bottles. I'll give it a try.

[boingy]

There is no arguing with the fact that PET bottles are slightly gas permeable and that over time small amounts of air will get into the bottle.
The big question is, how much air and does it have a significant effect?

Most people agree that PET is not suitable for long term storage but the exact time limit is very uncertain.

GW's opinions seem a bit unhelpful in this case, imho.
(I don't agree with his opinion of Videne either...)

Edit: - Coke do some great 1.25 litre bottles. Big enough to reduce the amount of bottles you need to clean, small enough to be drunk in one sitting and robust enough to pour without floppiness.

[vacant]

There is no arguing with the fact that PET bottles are slightly gas permeable and that over time small amounts of air will get into the bottle.

Given the pressure, I can understand how carbon dioxide from the priming sugar and air present when capped could gradually escape over time (and the bottle would feel more squashy). I don't understand how air would get in against such a pressure gradient?

[sparky Paul]

Given the pressure, I can understand how carbon dioxide from the priming sugar and air present when capped could gradually escape over time (and the bottle would feel more squashy). I don't understand how air would get in against such a pressure gradient?

It does sounds a bit odd, but it is correct.

Air is not entering the bottle, think of the the PET as a membrane which small amounts of gases can pass. The different gases in air, or inside the bottle, do no interact with each other, and the pressure of carbon dioxide inside the bottle will not prevent the passage of oxygen in the opposite direction, until equilibrium is reached - i.e. same amount of oxygen inside and outside. Carbon dioxide is lost to the outside.

Sounds fishy, but it's something to do with Dalton's Law IIRC...

[boingy]

And that's before you consider the fact that the bottle contains active yeast....

[shandypants5]

Given the pressure, I can understand how carbon dioxide from the priming sugar and air present when capped could gradually escape over time (and the bottle would feel more squashy). I don't understand how air would get in against such a pressure gradient?

It does sounds a bit odd, but it is correct.

Air is not entering the bottle, think of the the PET as a membrane which small amounts of gases can pass. The different gases in air, or inside the bottle, do no interact with each other, and the pressure of carbon dioxide inside the bottle will not prevent the passage of oxygen in the opposite direction, until equilibrium is reached - i.e. same amount of oxygen inside and outside. Carbon dioxide is lost to the outside.

Sounds fishy, but it's something to do with Dalton's Law IIRC...

You right Paul.

I always thought pressure would only ever flow from higher to lower, but apparently in some dissimilar gas cases it goes the wrong way.


There was a similar effect shown on this weeks "Coast" program.

Some boffin in Norway is using osmosis to make hydro electric power.

Basically it involved two chambers seperated by a membrane,
salt water in one (from the sea)
Fresh water in the other (from the river)

The fresh water keeps passing thru the membrane to try and balance the freshness/saltiness of the water on both sides, resulting in a huge pressure rise on the salt water side.

The idea is to use this pressure to drive a turbine.