Personally, I think there aren’t many more satisfying things you can do than crack open a cold beer after you’ve been hiking for a few hours, especially if it’s very hot outside.
Taking regular beer bottles or cans on a hike means the beer is warm by the time I drink it…and no one likes warm beer.
So can you put beer in your thermos flask to keep it cold? Or is there some reason you shouldn't put beer in a thermos? Will it break it?
Yes you can safely put cold beer in a stainless steel thermos flask. The beer will stay cold and carbonated all day and it won't cause any damage to stainless steel thermoses. Glass lined thermoses could potentially break from the pressure of carbonated beer – so you shouldn't put beer in a glass thermos.
Most modern thermoses are made from 18/8 stainless steel (also known as 304 stainless steel) and this is the same (or extremely similar) metal that beer kegs are made from. You don't have to worry about the beer corroding or ruining your thermos – beer and stainless steel work fine together.
The carbonation may make the lid more difficult to open, but this usually isn't an issue unless you leave the beer in there for days.
Some thermoses are still made with an interior of glass. While beer is non-reactive to glass the pressure from the carbonation in the beer could potentially be enough to crack the thin layer of glass.
The biggest issue with storing beer in your thermos is that if you don't clean your thermos out properly afterwards it can grow mold or continue to make your water taste funny.
Is It Fine to Put Beer in a Stainless Steel Thermos? Will it Break/Explode?
When I first thought about taking beer with me on the trail I did worry that maybe the carbonation in the beer would build up so much pressure that it would break my thermos.
However, this isn't the case at all.
The pressure from carbonated beer is relatively low (10-20 psi) and stainless steel thermos bottles can handle much higher pressures than this (around 200+ psi).
For reference, a plastic coke bottle can handle pressure up to around 200 psi before it breaks and stainless steel is much stronger than plastic.
The only thing that may happen is that the buildup of pressure inside your thermos may make the lid slightly harder to open than it usually would be. This is because the pressure is pushing the lid up increasing the friction on the threads.
This can be overcome by pushing down on the lid before turning or if you have a push button thermos then venting the pressure before opening it. There are also lots of other ways you can open a stuck thermos lid.
Can You Put Beer In a Glass Thermos?
Most modern thermoses are made of stainless steel but there are still some made with a glass interior (which was the original design) or you may have an old thermos that has a glass interior.
You should avoid putting beer in a glass thermos bottle. The glass is extremely thin and the small buildup in pressure from the carbonated beer could be enough to crack the glass and break your thermos.
Below you can see a snippet from someone on Quora who has broken a glass flask using carbonated soda. Soda would create a similar pressure buildup to beer.
On a few occasions ,I have put carbonated drinks ..what in the US are called Soda eg Fanta or Coke into a flask, and it would rupture the glass.Dan O Brien (Quora)
You could however store beer in a glass thermos if you left the lid slightly open so that the carbonation could vent out of the thermos and the pressure didn't build up.
While your beer might stay cold it'll become flat relatively quickly and this limits the transportation of your beer as the open thermos could easily leak.
Does Beer Stay Cold in a Thermos?
The purpose of putting beer in your thermos is to keep it cold for an extended period of time. But does it work?
Beer will stay cold in a thermos for around 3-6 hours depending on the outside temperature. To keep beer cold longer in your thermos add in some whiskey stones and the beer can stay cold for 12-24 hours.
These reusable stainless steel ice cubes chill your drink without diluting it. They are made from food grade stainless steel that is 1mm thick with an interior of 35% glycerin + water which has a freezing point of -12ºC (10.4ºF) - keeping your drinks even colder than regular ice cubes.
Exactly how long your beer will stay cold in your thermos will depend on a variety of factors such as the outside temperature, temperature the beer starts at, size of the bottle, how much beer you have in the bottle as well as whether or not you use ice.
How To Keep Beer Carbonated in a Thermos
The only thing worse than warm beer is flat beer.
When done correctly a thermos can keep your beer fizzy for days, but if you don't use it properly then your beer can go flat in your thermos.
Here's exactly how to keep your beer carbonated in your thermos.
Fill it all the way to the top
Make sure to fill your thermos all the way to the top leaving little to no air space at all.
If you leave air space the carbon dioxide dissolved in your beer will evaporate and fill the air space.
If this means using multiple beers to fill one thermos then so be it – do exactly that.
Keep The Lid Closed
After you fill up your thermos with beer close the lid and don't open the thermos again until you reach your destination and you want to drink your beer.
Opening the thermos regularly for sips will release a lot of gas and your beer will get flat fairly quickly.
Keep It Cold
The colder beer stays the longer it takes to go flat, which is why a thermos can actually be such a great way to store your beers.
Keep your thermos out of direct sunlight and away from warm items to keep your beer colder for longer and consider adding whiskey stones which act as ice cubes to keep your beer cold for longer.
What About The Taste? Will The Thermos Ruin The Taste of Beer?
It's normal to wonder whether or not the stainless steel from your thermos will alter or ruin the taste of your favorite beer (which might come out of a plastic lined can or from a glass bottle).
You've got nothing to worry about.
Beer is made in stainless steel vats, kept in stainless steel kegs and poured through stainless steel taps at the pub and it still tastes great.
Stainless steel is non-reactive with beer so your stainless steel thermos is NOT going to alter the taste of your beer.
If you feel it does then this may be caused from your lips/mouth touching the stainless steel to drink from the thermos.
To counter this you can get ceramic lined thermoses or you can pour the beer into a cup before drinking.