keeping water hot

[Sydney]

Last night I put my new Stanley vacuum bottle ("thermos") to the test.

The official claim on the box is that it will keep hot beverages hot for 12 hours if you preheat with boiling water for 5 minutes prior to pouring in your hot beverage, and that it will keep cold beverages cold for 24 hours (pre-chilled, presumably).

So last night I boiled enough water to mostly fill the bottle and preheated for 5 minutes. Then I filled it with boiling water and closed it tightly.

Then I left it sitting on the counter in an air-conditioned (about 72° F) kitchen for 12 hours.

Based on previous experience, I know I can't get water hotter than 205° F under normal conditions here, and the temp drops immediately once it's taken off heat.

After 12 hours, I poured 8 oz of water from the bottle into my thermometer-equipped measuring cup and registered exactly 153°.

The next experiment will likely be how hot the water will be after 12 hours when left outside on the porch, away from the air conditioning, although I have a few other ideas for follow-ups.

153° is less than my preferred temp for making green tea, but is just right for yerba mate, for which I'll go as low as 140° with very satisfying results.

I also figure I can heat water from 153° to an ideal green tea temp on a pocket rocket stove in well under a minute (another of the follow-up experiments planned).

Some of you who know me a bit are aware of how I reeeeeally want my tea after a hurricane or other disaster rolls through, so this sort of information is the sort of thing that I really do like to know before my neighborhood becomes a third world country like it did after Katrina and other occasional bits of trouble.

[taitea]

Interesting tests. I'd be curious to know how long it takes the water to drop, say, 5 degrees once you have put it in the thermos. Of course this might be a bit tricky to do without tampering with the experiment.

[Sydney]

Some of my other ideas:

How much temp drop after 4 hours, 8 hours, etc.?

*Exactly* how hot is the water I'm putting in before closing the bottle? (potentially challenging to be precise on that)

How does the temp hold up after I pour some out for tea, leaving more air in the bottle? (assumption being that this would result in heat loss)

Does re-boiled water make a difference? (because on Food Detectives, they said that reboiling water removes oxygen from the water)

[omegapd]

How does the temp hold up after I pour some out for tea, leaving more air in the bottle? (assumption being that this would result in heat loss)

I have the same thermos. I can tell you without a doubt, that if you pour some out, you will have lukewarm water in 2 hours.

EW

[betta]

The cooling rate depends on many parameters, mainly the insulation technology, material, surface and also the environment temperature.
The main technology for this, mainly vacuum silver coated glass or vacuum stainless glass. The former one is better than the latter, however it's not 'implosion hazard-free'.
Good insulation jar should have cooling rate about 3-5°C/h more than that, is either bad insulation jar or there's a defect in the manufacturing process.
I think thermos is one of the leader in the thermal insulation technology, so it shouldn't perform so poor. If the jar isn't vacuum anymore, fast cooling rate will happen. Please keep in mind to flush the cold jar first with hot water before pouring the actual hot water to get the best result.
Mine is made by local company and after 8-10 hours I still get 70-80°C water.
The re-boiled hot water stored in insulated jar doesn't taste very good.

[taitea]

The re-boiled hot water stored in insulated jar doesn't taste very good.

What do you mean by this? If you boil water and then stick it in the thermos for a couple of minutes, will the water taste bad? Will it have dropped significantly in temperature?

[betta]

The re-boiled hot water stored in insulated jar doesn't taste very good.

What do you mean by this? If you boil water and then stick it in the thermos for a couple of minutes, will the water taste bad? Will it have dropped significantly in temperature?

If you boil again the water which was previously already boiled and stored in the insulated jar, the taste will change.
Dependent on the insulated jar material, it might also change. Coated glass is neutral but stainless steel material will also affect the taste.

If the insulated jar is good, the temperature drop shouldn't exceed 5°C/h, then the temperature of boiled water which is just poured into the jar shouldn't drop so horribly.

[soapy]

we have one of these and don't use it very often... when we do we drink it up very quickly.....

[taitea]

I was wondering if a thermos could be a possible solution to having consistently hot water for gong fu brewing, but it sounds like a less than perfect solution.

[Sydney]

Yeah, I don't think of this as a tremendous aid to daily fu. It's just hurricane season down here, and we're bracing for the next set of problems.

Fortunately, hurricanes give you some warning so you can do things like prep water. Tornadoes and such are less civilized.

[betta]

I was wondering if a thermos could be a possible solution to having consistently hot water for gong fu brewing, but it sounds like a less than perfect solution.

I'm using it since the very beginning to provide continuous hot water to brew my tea according to gongfu brewing method.
First, I don't spend more than 2 hours for enjoying the tea, so the water temperature won't fall below the desired temp.
Second, I use glass coated insulated jar, so taste of water isn't influenced by the material of the insulated jar
Third, I use normally below 200 mL water so 5 steep at that volume should be enough for me.
I found the idea cute and it's perfectly fine for me.

PS: the screw type lid of insulated jar keeps the temperature much better than any other type of lid.

[Chip]

Some things that could help.

After dumping the first boiled water from the thermos, pour another round of boiled water in, and then the final batch.

Also, wrapping the thermos in towels or newspapers or other insulating material should reduce heat loss? And if you are crazy enough, final wrapping with a vapor barrier to eliminate air exchange around the valuable package.

Desperate times call for desperate measures, this could make a difference of 5-10 degrees? I would be curious, but not curious enough to try.

[Sydney]

Is Chip challenging the TeaScientist????

[Chip]

Planting seeds... If you won't try it, nobody will.

Watch out for Gustav, and may the only hot water you are in, be the water in your thermos.

[betta]

Some things that could help.

After dumping the first boiled water from the thermos, pour another round of boiled water in, and then the final batch.

Agree and I've been doing it all the time

Also, wrapping the thermos in towels or newspapers or other insulating material should reduce heat loss? And if you are crazy enough, final wrapping with a vapor barrier to eliminate air exchange around the valuable package.

Too extreme, but plz let me know if anyone here tried it before