PET Bottle looks like a grenade

[Luxy]

Hi guys,

Bottled 2 1liters PET bottles 4 days ago, because of their squarish shape, they are beginning to look like a giant grenade to me. I read somewhere they withstand pressure better than a glass equivalent. I am beginning to worry that it might explode and shatter other glass bottle stored together with them. I tried to unscrew one of it slowly to see if I can let out some gas but I think I turn it maybe 2 turns but still no gas release and I gave up thinking it might gush out soon as any gas is release and mess up the place. Should just leave them be?

 

[VikeMan]

It's normal for plastic bottles to expand a bit when the beer (or cider or whatever) carbonates. Did you practice good sanitation and was your fermentation finished before you bottled and did you use an appropriate amount of priming sugar for the volumes of CO2 you want? If so, there should be nothing to worry about.

 

[mac_1103]

What kind of beverage came in the bottles originally? It looks like a juice bottle and I'm not sure how much pressure those are designed for. But anyway, the bottle is bulging because it has to. The total volume of liquid and gas after the priming sugar ferments is greater than the starting volume of beer and priming sugar. When I prime in PET soda bottles I squeeze the air out of the headspace and the bottles return to their normal shape when they're carbonated.

If you're really worried, put the plastic bottles in a sturdy container far away from the glass bottles.

 

[Luxy]

Yeah I clean them with bottle brush and sanitize with StarSan before racking beer into them. For 1 liter I added 12grams of normal household sugar(2 and half teaspoon as per below. The beer was in the fv for 3 weeks. Thanks for the reply

 

[Luxy]

Hi Mac,

They originally used to store tea kind of drink. Should I be worry? I stored them away from my other bottled beer already being so worried about it bursting in the middle of no where. Hey thanks for the tips. Will squeeze out any air possible the next time so they have more room for expansion during secondary. My other PET bottles were originally used for carbonated drink but i find the original drink not as fizzy as the usual cola or 7-up. Is it better to use Cola, pepsi, 7-up PET than using other non originally used for fizzy drink bottles?

 

[whoaru99]

Hi Mac,

They originally used to store tea kind of drink. Should I be worry? I stored them away from my other bottled beer already being so worried about it bursting in the middle of no where. Hey thanks for the tips. Will squeeze out any air possible the next time so they have more room for expansion during secondary. My other PET bottles were originally used for carbonated drink but i find the original drink not as fizzy as the usual cola or 7-up. Is it better to use Cola, pepsi, 7-up PET than using other non originally used for fizzy drink bottles?

Worry... well, dunno, but next time I'd use something you know has reasonable pressure capability like a highly carbonated drink bottle, sparkling water perhaps.

Far as squeezing it down, I think that wouldn't matter much, if at all, in terms of managing the pressure.

 

[DBhomebrew]

'Room for expansion' sounds like 'volume that must be accounted for in priming calculations to arrive at desired pressure'.

If a bottle's going to bulge at 2vol, it's going to bulge at 2vol whether or not it started with squeezing the air out or not.

That said, if x grams of priming sugar creates 2vol without first squeezing the air out, the same x grams will create something less than 2vol by first filling 'room for expansion' before creating pressure.

 

[bruce_the_loon]

My concern on that bottle would be that the cap does not look like a high pressure cap. It looks more like the flat, wide cap I see on fruit juice bottles and takes less than one turn to remove from the threads. Was the cap a rigid plastic or somewhat flexible?

The bottles used for Pepsi and other fizzy drinks have rigid caps that thread tightly onto the bottle with a few turns. It is that style of cap that I get if I buy PET bottles for beer from my beer supplies store.

These days 2.25l cola bottles are just as thin and flexible as the ones I get non-fizzy drinks in and they still hold up to the pressure. It is the cap that is the weak point and I'd be concerned with a flexible and wide cap that the pressure inside might distort it enough to pop it free from the threads. You won't get bottle bombs exploding into fragments, but you might get a beer shower.

Since you've isolated the bottles already, I'd leave them be until either they pop their tops or you can drink the beer. Then get some Pepsi etc bottles with the smaller, deeper caps for the future.

 

[MaxStout]

As others noted, bottles like that are not intended to hold pressure. It's likely the same kind of plastic as with pop bottles (PET), but doesn't have the indentations to withstand pressure, and it may be thinner material.

It'll probably withstand some pressure, but who knows how much. Looks like there's a sizable amount of headspace, which will compress some.

Maybe crack open the lid a little to vent off some of the CO2.

Or keep it isolated, like in a bucket, just in case it pops off.

Then get yourself some PET soda bottles for next time.

 

[VikeMan]

For 1 liter I added 12grams of normal household sugar(2 and half teaspoon as per below.

12 grams of table sugar in a liter of beer? If so, you're looking at about 3.9 volumes of CO2. That's very high. I'd be very careful with any of your bottles, plastic or glass.

ETA: teaspoons isn't a good way to measure priming sugar, but if you did measure that way, maybe you'll get lucky.

 

[fluketamer]

only use pet bottles with the crimped bottoms. if you notice in the picture you posted for reccomended sugar amounts, , the bottom of the bottles are all crimped. you dont have to squeeze out the air but can if you want to . i have had the caps bulge and even crack when i over carb them. they can hold a lot of pressure without bulging or breaking

btw i think that bottle may blow. i would cover in thick towel and slowly open to degas.

and you cant clean PET bottles with a regular bottle brush it scratches the plastic and will harbor all sorts of bugs.

you need a soft cloth bottle brush which i cant seam to find in the US

 

[Luxy]

@bruce_the_loon the caps are rigid like the regulars found on any pepsi cola, and my bad for not taking the full picture, there are atleast another half of the cap cut off above the photo that probably leads to the suspicion of the cap not having the regular amount of threads but they do atleast 4-5 complete turns to open or close.

@MaxStout with your advice I manage to get the courage to degas them manage to release them without any gushing spillage, while degassing I also squeeze abit so they have more room for expansion should the fermentation of the balance priming sugar in the bottles continue but careful enough to let gas out and close up the cap immediately without letting the bottle sucking in any O2 before releasing the squeeze.

@VikeMan I did not use teaspoon for the priming sugar as I have bought those small sachets of 3 grams of sugar before hand only for this priming purpose and emptying them into the bottle as many as the total sugar called for. 12grams is a lot for 1 liter? Is the guide photo for the priming too much sugar?

@fluketamer I have got some of these I think they are what you have described as crimped and yeah I only manage to summon the courage to degas them after seeing MaxStout and your advice Ooook noted on the PET cleaning advice will check out more in the forum regarding reusing and cleaning procedure for them.

 

[VikeMan]

I did not use teaspoon for the priming sugar as I have bought those small sachets of 3 grams of sugar before hand only for this priming purpose and emptying them into the bottle as many as the total sugar called for. 12grams is a lot for 1 liter? Is the guide photo for the priming too much sugar?

Yes, 12 grams is too much for 1 liter, unless you are shooting for about 3.9 volumes of CO2, which is very high and potentially unsafe unless you're using very sturdy bottles (like champagne bottles or "belgian" bottles). I don't see on your photo where it calls for 12 grams. I see teaspoons, which is not a reliable way to measure sugar for priming. Also, I strongly suspect your photo is referring to corn sugar (glucose/dextrose), not table sugar (sucrose). With table sugar, you need less of it than you would need of corn sugar (which contains water) to get the same level of CO2.

 

[bobtheUKbrewer2]

the priming sugar table in post 4 looks a bit heavy to me - I use less than half those rates.

 

[InspectorJon]

Yeah I clean them with bottle brush and sanitize with StarSan before racking beer into them. For 1 liter I added 12grams of normal household sugar(2 and half teaspoon as per below. The beer was in the fv for 3 weeks. Thanks for the reply


View attachment 845346

I would not trust this priming table (post #4 above). The sugar does not increase proportionally with the volume and it does not say what kind of sugar.

 

[mac_1103]

Yes, 12 grams is too much for 1 liter, unless you are shooting for about 3.9 volumes of CO2, which is very high and potentially unsafe unless you're using very sturdy bottles (like champagne bottles or "belgian" bottles).

Actually, PET soda bottles are rated for higher pressures than any widely available glass bottle that I know of. At least according to this. Still not sure about these tea bottles though.

Bottle type​	Max. CO2 Volumes​
12oz​	3​
33cl Belgian​	3.5​
500ml European​	3.5​
Swing top​	4​
Champagne​	7​
PET​	10​

 

[fluketamer]

I would not trust this priming table (post #4 above). The sugar does not increase proportionally with the volume and it does not say what kind of sugar.

i have carbed in PET soda bottles at those rates and even higher. it makes very fizzy beer. the bottles wont burst as long as they are soda bottle.


the reason its not proportional in that picture is cause mr. beer ( the maker of that pic) doesnt expect people to have the ability to measure out 1/4 of a teaspoon . so some of those amounts are rounded off.

Actually, PET soda bottles are rated for higher pressures than any widely available glass bottle that I know of. At least according to this. Still not sure about these tea bottles though.

Bottle type​	Max. CO2 Volumes​
12oz​	3​
33cl Belgian​	3.5​
500ml European​	3.5​
Swing top​	4​
Champagne​	7​
PET​	10​

yes they take MUCH higher pressures than glass

some swingtops wont take pressure very well and will blast the swingtop off when opening which can be dangerous.

 

[VikeMan]

the reason its not proportional in that picture is cause mr. beer ( the maker of that pic) doesnt expect people to have the ability to measure out 1/4 of a teaspoon . so some of those amounts are rounded off.

If true, this completely shatters my illusions of Mr. Beer as a leader in applied brewing science.

 

[Luxy]

@VikeMan ah I used the lay man method and google for 1 teaspoon sugar in grams which comes to about 4grams per teaspoon but I still end up having more than necessary. Looks like I gonna be careful opening those swing caps or PET for those I primed with Mr.Beer's guide.

I have then researched and found for priming with sucrose(table sugar) here https://www.brewersfriend.com/beer-priming-calculator/
Then googled the avg volume of CO2 for beer found to be around 2.2~2.6 is this accurate? Stout has lower CO2 to be around 1.X

 

[VikeMan]

@VikeMan ah I used the lay man method and google for 1 teaspoon sugar in grams which comes to about 4grams per teaspoon but I still end up having more than necessary.

The problem is that these rules of thumb vary. And they vary for a good reason, i.e. that measuring sugar by volume is not an accurate way to get a desired mass. That aside, your math is a bit off... your chart said 2.5 tsp, which you presumably multiplied by your 4 grams per tsp rule of thumb. The result there would be 10 grams, not 12. And I'll just mention again that the author of that chart (Mr. Beer, apparently) almost certainly meant corn sugar, not table sugar, which means that even if the chart was perfect, table sugar would overshoot the mark. That's because of both the water content of corn sugar and the fact that table sugar is denser.

TLDR: Use a scale and use computations appropriate for the sugar type.

@VikeManI have then researched and found for priming with sucrose(table sugar) here https://www.brewersfriend.com/beer-priming-calculator/
Then googled the avg volume of CO2 for beer found to be around 2.2~2.6 is this accurate? Stout has lower CO2 to be around 1.X

The best CO2 level for any beer depends on both style and personal preference. Personally, I wouldn't normally carbonate a stout to "1.X " (i.e. less than 2) volumes.

If in doubt for a given style, 2.5 volumes is IMO a reasonable default, and is, I think, pretty close to the average, at least in the USA.