Inconsistent results with PET bottles?

[chrisbardell]

Just done a brew (Coopers Preacher's Hefe wheat beer). All went fine, no probs with primary (full 23L, OG 1040, stable FG 1010), batch-primed 175g raw cane sugar, bottled into new 500ml PET bottles. Just completed 2 weeks secondary + 2 weeks cool.

Have now tried 4 bottles. Two were spot-on - bottles rock-hard, good fizz on opening, nicely carbonated. Two were knackered - bottles squidgier, barely any fizz on opening, and flat as a pancake beer.

I made a point of double-checking that the screw-caps were on nice and tight at bottling time. Puzzled at the different levels of carbonation, given that I batch-primed. All bottles identically sanitised, rinsed, and drained. All bottling done in one go.

Just did a squeeze test on the remaining bottles; about a 50/50 split between rock-hard and squidgy. The bottles I used were from two different boxes - possible one box were microscopically faulty?

Any ideas on this? Grateful for any help. Meantime I've taken the 18 squidgy bottles out of the shed and brought them indoors. Not sure if a couple of weeks in the warm might re-trigger some fermentation and rescue them (?)

 

[chrisb8]

The other thing to consider is how you batch primed. Did you put the sugar in in granular form or dissolve it in boiling water first? If it wasn't fully dissolved then you may have ended up with inconsistent levels of priming throughout the batch.

I have found with the coopers pet bottles that the caps have to be on super tight otherwise they can leak pressure. So tight that they are a pain to open again. I use a couple per batch to check carbonation but otherwise I'm not a fan.

 

[Appleyard]

I had a bit of bother with PET bottles, which I have not used before.

https://www.thehomebrewforum.co.uk/threads/bottle-bother.91351/#post-982753
Thinking aboout it, I would be tempted to submerge a bottle in a bucket of water, upright, and squeeze it hard. Even a tiny leak should show up.

I'm also unsure about doing the lids up really tight. On examining the seal, it seems that the inside of the top of the bottle and the outside of a plastic ring or flange (pardon me) is what creates the seal, and overtightening it might lead to distortion of one's compomnents.

For the same reason, I am now being much more careful of the neck of the bottle (with brushes and whatnot when cleaning).

The bottles I've been using are "recycled" 2L PET cider bottles, but I'd guess most are the same sort.

Edit: Hm, this seems to be a major topic in "containers", and there's a lot to it, from the design of the cap to the closure method to the torque applied to the cap when putting it on (and taking it off). I don't think that enormous force should be or should need to be used when putting on my cider bottle caps. Details all over the place but gentle intro at:

http://allthingsmechanical.blogspot.com/2008/09/plastic-bottle-cap-design.html

 

[chrisbardell]

Thanks for the suggestions. Should have mentioned that I batch-primed with boiling water, dissolved sugar, cooled.

The PET bottles I bought weren't Coopers ones, but take your point about the caps.

I picked up a set of glass 500ml bottles 2nd hand off eBay recently, and have used them no probs for a batch of stout that I made. Basic 2-lever capper was easy to use, and every bottle so far has been properly sealed.

I think I'll take the hit and ditch all but a few PETs for monitoring carbonation, as per your method. I was about to bottle a batch of Coopers European Lager for the recommended 3 months cool conditioning, and it would break my heart if it ended up spoiled after all that time. Thinking I should get some more glass bottles and stick with them from now on.

Cheers again for your time.

 

[chrisbardell]

I had a bit of bother with PET bottles, which I have not used before.

https://www.thehomebrewforum.co.uk/threads/bottle-bother.91351/#post-982753
Thinking aboout it, I would be tempted to submerge a bottle in a bucket of water, upright, and squeeze it hard. Even a tiny leak should show up.

Thanks for that link, didn't spot it the other day. Very useful info there. I'll have another read and work out a plan.

Appreciate your time.

 

[Appleyard]

Thanks for the suggestions. Should have mentioned that I batch-primed with boiling water, dissolved sugar, cooled.

The PET bottles I bought weren't Coopers ones, but take your point about the caps.

I picked up a set of glass 500ml bottles 2nd hand off eBay recently, and have used them no probs for a batch of stout that I made. Basic 2-lever capper was easy to use, and every bottle so far has been properly sealed.

I think I'll take the hit and ditch all but a few PETs for monitoring carbonation, as per your method. I was about to bottle a batch of Coopers European Lager for the recommended 3 months cool conditioning, and it would break my heart if it ended up spoiled after all that time. Thinking I should get some more glass bottles and stick with them from now on.

Cheers again for your time.

I've been using glass since the year dot minus one, but I thought 2L PET bottles might be actually better, because carbonation should be easy enough to monitor, and they should seal easily, and filling up one bottle instead of four is appealing. However, I will keep using glass ones because I think they're somehow "nicer". I wouldn't be hasty and chuck out your PET ones without ivestigating. I've got a 2-lever capper (Boots?), as well as the hammer-on sort, both of which seem to work well. However, PET bottles shoud seal well.

I'm triping this as I go, and pokijng around on the 'net as I go, so forgive the delay. This: PET Bottles in Homebrewing seems to say "beer in re-used PET bottles a few months only", but I am unsure that this can be right. It also says there's something "spcial" about PET bottles sold specifically for home brewing. There's a lot of not-very-scientific guesswork and flat-out statement with little fact.

Hm. I remember buying Ruddles County and other beer, plus various different ciders in 2L PET bottles, so.... let's look at the "best before".

My re-used 'orribles (in Tesco Crofters cider bottles), purchased in the last month or two, all seem to have "BBE Aug 2021" on them. So that's 9 or 10 months. But when was it actually bottled? This year, any guesses?

Perhaps it's time to go around supermarkets, looking at what's on sale in 2L PET bottles, and what the BBE is.

I do hear that beer in PET bottles is fairly frequently sold outside the UK. Any ideas about that, anyone?

 

[Scrattajack]

As I understand it, PET is permeable and some effort goes into making sure the bottle is appropriate for the beverage in question. The bottles sold for homebrew, such as Coopers, are multi-layered (triple-walled, I think) to make them suitable for beer.

 

[Slid]

In my experience, if the Coopers bottles are squidgy after 2 weeks in the warm, the top was not put on fully. First use with the old coopers tops was complicated by the tamper proof ring at the bottom, which detatches on first unscrewing (in theory). The newer tops are easier in that respect. I would not advise on over tightening the tops as this is unnecessary. If you have half and half carbed, I suspect the batch priming has gone astray. You could re-pour your "flat" bottles into an FV, re-prime and re-bottle. Won't do any harm, but is a big faff at this stage.

 

[chrisbardell]

If you have half and half carbed, I suspect the batch priming has gone astray.

Aha, you set me thinking and I think you have nailed it. Went back to my notes for that brew - looks like I syphoned into the bottling bucket, sealed it up, and then had to go off for an hour or so to make dinner for everyone. Then went back to it afterwards and did the bottling. By the time I finished the bottling, it had probably been sat there in the BB for 1.5-2hrs total.

I wonder if a lot of the dissolved priming sugar has gradually sunk towards the bottom of the bottling bucket during that time. I'm guessing that rather than a 50/50 split of primed/underprimed, I probably have a spectrum of primed/underprimed, depending on what order I filled each bottle. Used a tapped BB with a bottling wand, so the first ones out were probably the best ones, if the sugar had sunk to the bottom.

Cursing myself a bit, but I'm still learning. Going to chill some of the underprimed ones for later on and try a vigorous pour into a jug to liven them up a bit, and see if they're drinkable. Agree that to unbottle/re-prime would be a palaver.

Thanks for your time & to the other repondents. I think it's pilot error after all.

 

[JockyBrewer]

A couple of things from previous issues I and others have had with PET bottles:

1. Tighten the cap by hand when filling. Go back at the end of filling or an hour or so later and tighten them again. The caps give a bit and lose part of their seal.
Don’t use tools to seal them - over torquing them breaks the seal again somehow.

2. Use only the real Coopers bottles and caps. Cheaper brown PET bottles are available (they have a shoulder that slopes up to the base of the lid, rather than a long neck like the coopers ones), and I’ve had a lot of badly oxidised beer from them. No idea why, I’d just avoid them.