Thermal Flask for Coffee

Not sure about the flask as we take bottled water to drink. OK mostly but recently I picked up a bottle of sparkling (by mistake of course) and opened it at about FL90 with disasterous (and hilarious for the family with me) results but as it was only water it soon dried. I now check VERY carefully.

The thing which makes coffee exciting is not simply the pressure delta, but that water boils at a lower temperature at altitude. So when you open the flask, the pressure inside suddenly drops. What was initially a happy, sub-boiling-point, pressurised liquid immediately becomes superheated at ambient pressure and starts boiling furiously.

Fortunately I discovered this from someone else’s empirical experiment rather than my own.

I think it will be ok if the flask is upright and you open the top slowly, to release the pressure.

Regarding the liquid suddenly boiling again, you would need to be pretty high for that. See here

Even at 30000ft the boiling point is +70C and if the coffee was that hot you would be suing Macdonalds

It may be different with other liquids. I once opened a hot (due to sunlight) Coke can in a car and most of it emptied itself all over the car. At sea level…

I was once a passenger and I opened a bottle of coke for the pilot. We were much lower down….maybe 4K-5K feet. It was ok, but I had to slowly release a bit of the pressure and then close, and repeat a few time. But it was ok. After doing that, I took the second bottle for myself, and without thinking opened it quickly, and sprayed plenty on myself!

So hence I was faced with the option of spending the next 2 hours in a sticky wet top, or trying some acrobatics in a PA28 to get a chance of clothes out of the over packed luggage back, and change my top! I choose the second, and about 20 minutes later, I’d learnt a lesson about opening stuff slowly at altitude!

Many flasks have a “Pour” opening which allows you to partly open the top, without actually removing it, so that you can pour some out. If attempting to open it, I suggest you don’t go any further than that Pour part, until the pressure equalises. That way you can quickly close it again if necessary.

No experience with Coffee in a thermal flask, but..: I had a roller pen in my kneeboard which exploded at 16000ft :-(

Thank you :) Luck of the Irish eh?

@dublinpilot: Is it really tomorrow? Hinda sends her best!

Nope…today

Thanks :)