Plastic bottle–in–titanium bowl double-boiler. Safe?

[Jeremy Greene]

Assuming the bowl is never allowed to boil dry, is the pictured assembly safe? What plastics are and are not safe for this assembly? (Discussion of *evil* plastics being unsafe at *all* temperatures is off-topic.)

[Rick Dreher]

Hi Jeremy,

With water in the pot and water, or dinner, in the bottle there may well be enough heat transfer to keep the plastic from melting to the pot base. That said, if you raise the bottle in some fashion even a small amount from the pot base, you'll be guaranteed water will circulate and keep it safely cool. Even a few pebbles would do the trick. Variables include the stove's flame pattern, the pot's metal and the type of plastic. For example, with a straight upward flame type stove and a titanium pot, I'd want a layer of water between the bottle and the pot.

(As to the off-topic topic, I'd at a minimum mind the type of plastic bottle used and choose one intended to hold hot liquids.)

Cheers,

Rick

[Roger Caffin]

You definitely need to raise the bottle off the pot! As Rick said, otherwise the plastic will stick to the pot.

But there is another problem: when the water boils under the bottle it will form a bubble of steam, and things can get very 'interesting' then. The bottle may start lurching all over the place as the steam builds up and escapes, and the pot could get a bit hotter than you expected.

So keep a gap between bottle and pot.

Cheers

[. .]

Hi Jeremy,

That bottle looks to be one of the older Nalgene Polycarbonate (Lexan) bottles that were discontinued by many retailers (MEC, REI, etc.) over concerns of BPA. Whatever harmful chemicals may be found in plastics, increased risk certainly arises when heat is applied.

Have you thought about using a ti mug or stainless water bottle? What specific application are you trying to use this for? Fondue? It has never occurred to me to use a double boiler on the trail, but if it did, I would probably use nesting Ti pots, such as BPL Firelite 550 + Evernew 450 mug. The mugs folding handles should greatly aid in stabilizing and the combined pots weigh less than just the Nalgene bottle.

[Jeremy Greene]

Thank you all for the prompt and well-thought safety guidelines. I play a bit in the kitchen. I wanted to see if I could find another application for the revered Nalgene bottle.

Method: The length of 2 wooden popsicle sticks was reduced to equal the diameter of the bottom of the titanium bowl. They were notched and assembled into a cross to stand on edge. The crossed sticks, with water up to the 1 cup line were placed in the bowl. A 1/2-full Nalgene bottle set on the sticks displaced the water level to the 2 cup line. Shortly after water in bowl began to boil, it got "interesting," even before the water level was reduced. A flame level could not be found between high enough to heat the bottle water and low enough to keep the bowl water from foaming onto the flame. The bottle water was not successfully brought to a boil.

Conclusion: I didn't find another application for the Nalgene, but the notched and crossed popsicle sticks (1 gram each, before cutting) may be an elegant solution for steam baking. The joinery can be loosely made with a pocketknife, because wood swells in water.

[Rick Dreher]

Thanks for reporting your results, Jeremy. The popsicle stick idea is darn clever! Salted away for future use.

I'll guess too little of the bottle was immersed to heat up.

Cheers,

Rick

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