Stovetop Pasteurising... how safe are "ordinary" bottles

[Chalkyt]

Sorry this is a bit long winded.

It is getting close to cider making time for us in the bottom half of the world. I want to try stovetop pasteurising some cider this year in order to make a "sweet" cider. I don't want to use Xylitol or any of its mates but I did get a good taste from using about 20% pears (I guess this provided some natural sorbitol).

The plan is something like bottle at SG 1.007 then pasteurise at 1.005. My concern is what pressure builds up in the bottle when it is heated to say, 150 degrees. Also what happens in terms of pressure if the pasteurising doesn't work to kill the yeast and it goes down to 1.000 where I end up with something like 5 atmospheres (75psi) of carbonation, (apart from having a very fizzy drink).

From what I can glean from Dr Google, normal beer bottles will happily accommodate 3 atm (45psi) and might typically fail at something like 150psi, which only gives me a safety factor of 2X if the above goes pear shaped and I end up with 75psi in the bottle, without considering any short term pressure from heating the contents.

I don't know if I am getting a bit flakey about a problem that doesn't exist, or is this all sailing a bit close to the wind and getting into bottle bomb territory if it goes wrong.

Anyone successfully gone down this path? Also any mechanical engineers out there who would like to comment.

 

[Hoppy2bmerry]

This sticky goes through the process. It may not match up with all the info on google, but people haven’t had issues following the recommendations.
https://www.homebrewtalk.com/forum/threads/easy-stove-top-pasteurizing-with-pics.193295/

 

[Maylar]

Sorry this is a bit long winded.

The plan is something like bottle at SG 1.007 then pasteurise at 1.005. My concern is what pressure builds up in the bottle when it is heated to say, 150 degrees. Also what happens in terms of pressure if the pasteurising doesn't work to kill the yeast and it goes down to 1.000 where I end up with something like 5 atmospheres (75psi) of carbonation, (apart from having a very fizzy drink).

Pressure and temperature are directly related. Knowing the SG is a good idea, but monitoring pressure is better. See below.

From what I can glean from Dr Google, normal beer bottles will happily accommodate 3 atm (45psi) and might typically fail at something like 150psi, which only gives me a safety factor of 2X if the above goes pear shaped and I end up with 75psi in the bottle, without considering any short term pressure from heating the contents.

All bottles aren't created equal. Considerable debate exists on that on the web. I've read that commercial breweries test their bottles at 100 psi, but I know some of the cheap bottles I've bought off Amazon are noticeably thinner than my recycled beer bottles.

I don't know if I am getting a bit flakey about a problem that doesn't exist, or is this all sailing a bit close to the wind and getting into bottle bomb territory if it goes wrong.

Anyone successfully gone down this path? Also any mechanical engineers out there who would like to comment.

Electrical Engineer by education (geek) but I dabble in the technical realm. Here's a thread I did a while ago on bottle pasteurizing:

https://www.homebrewtalk.com/forum/threads/cider-carbonation-experiments.513435/#post-6649065

 

[Chalkyt]

Thanks for the replies. The stovetop sticky started me down this path and of course the threat of bottle bombs has made me cautious especially as a failure to stop the yeast suggests that somewhat scary pressure numbers could result.

Maylar, your 2015 thread is just what I was looking for. It seems that we both have the same background (Electrical Engineering) but I am afraid that I tended to skip over hydrodynamics and other "mechanical" stuff.

I use mostly recycled 333ml beer bottles which should happily withstand 2.5 vols of CO2 (around 45psi). I generally aim for 2.0 vols or less (@25psi = the bottom end of Petillant). According to CJ Table 15.3 around 0.002 change in SG should (and does) result in that level of carbonation.

So, it might be worth replicating your pressure gauge setup to monitor what happens to the pressure inside the bottles during pasteurisation. CJ recommends 10 minutes at 149F (65C) for pasteurisation, which is a bit less than what you were aiming for. Neverthless the pressures that you saw are a bit concerning and my geeky engineering brain is looking for the "belt, braces and safety pins" path.

Some of my bottles are twist tops (do you have them in USA?). They take crown seals which can be removed by twisting rather than finding a bottle opener. They seem to seal OK so it might be possible to fit a pressure gauge to them.

Watch this space!

 

[Blacksmith1]

You are better off replacing them as you can with pry off type bottles. As i understand it they are a little thicker, and seal better.

 

[Chalkyt]

Yes, I try to salvage the pry off types. Most of the premium local and imported such as Peroni, Corona etc are still pry off, but the local regular beers seem to be going to twist top and I have noticed that those bottles do seem a bit flimsier..

 

[Blacksmith1]

It's really hard to find bottles that are not twist off. Even some of the so called premium brands here are twists.

 

[MarkKF]

I have accidentally used twist offs. I've been told that capping can break them. Never happened to me. But I have broken them trying to get the cap off!