Milk it up!

November 21, 2008 7:55 AM

Is it OK to keep tea+milk in a thermos for 24 hours before drinking?

Recently my wife has been doing overnight call at her hospital (30 hours working in the hospital at a time). To make it a little easier for her, I have been filling a vacuum thermos with hot tea (with milk... English tea basically) for her to drink.

My wife usually drinks the tea a full 24 hours after I put it in the thermos and while the tea is still hot (awesome thermos), I are wondering if it is still safe to drink the milk.

Is the milk still safe after sitting in a hot thermos for 24 hours?

posted by chrisalbon to food & drink (18 answers total)

Its fine. The stuff she touches in her work environment has a higher probability of giving her problems than that will.
posted by allkindsoftime at 8:01 AM on November 21, 2008

It might not be possible but the tea will taste a lot better if you're able put the tea and milk in separate flasks.
posted by ceri richard at 8:11 AM on November 21, 2008

How about bringing some powdered milk, and letting your wife add it closer to the time that she's going to drink it?
posted by aleahey at 8:16 AM on November 21, 2008 [2 favorites]

This is what we call "boat tea"... the stuff that's been sitting in a flask since we started sailing over a day ago. It will taste terrible, but is perfectly drinkable.
posted by methylsalicylate at 8:37 AM on November 21, 2008

You used to be able to buy vacuum flasks that had a milk container screwed to the bottom of the flask.
posted by mandal at 8:57 AM on November 21, 2008

According to ServSafe (the entity that certifies people in food industries for food sanitation and safety): The Temperature Danger Zone is the temperature at which bacteria multiply rapidly. The TDZ is from 41 degrees Fahrenheit to 140 degrees Fahrenheit. Foods should not be allowed to stay in this temperature zone for more than 2 hours (1 hour on a very hot day).

Offhand, I know that campylobacter can be found in milk products and it can cause gastroenteritis. Have I ever become ill from milk? No. She'll need to weigh the risks herself, as IANAD nor am I a foodborne pathogens expert. I agree with ceri richard, though, in that the tea will likely taste a lot better if the milk and tea were stored separately and added as needed.
posted by cooker girl at 9:11 AM on November 21, 2008

See my previous AskMe here. The tea starts tasting terrible but it doesn't make you sick.
posted by proj at 9:18 AM on November 21, 2008

Milk should be fine, but it would be better for freshness and flavor if she poured the tea from the thermos into a mug and *then* added milk.
posted by grapefruitmoon at 9:25 AM on November 21, 2008

Skip it and keep it separate as others have suggested. Because it'll be fine until it's not, and if that happens, it'll be gross for all involved.

I can't be sure, but I doubt that the thermos would keep the liquid inside above 140 degrees Fahrenheit for 24 hours. Staph aureus is all over the place, for instance, and it's fairly easy to contaminate things. If she does get a bug, she'll be miserable for a couple of days and probably won't enjoy tea and milk for some time. Why take the risk, however small? Have her leave some milk in the fridge at work.

See my previous AskMe here. The tea starts tasting terrible but it doesn't make you sick.

This is wrong. It can make you sick. That doesn't mean it will, but it is possible. Using our example, here's what CFSAN says about the effect of heat on Staph: "Exposure times [of S. aureus contaminated food stuffs - batter, specifically] greater than 12 hours for temperatures between 50°F (10°C) and 70°F (21.1°C) could result in toxin formation. Exposure times greater than 3 hours for temperatures above 70°F (21.1°C) could also result in toxin formation."

Don't be a hero, Billy.
posted by averyoldworld at 9:46 AM on November 21, 2008

See my previous AskMe here. The tea starts tasting terrible but it doesn't make you sick.

Weirdly, none of the answers to that question mentioned the obvious, which is to boil up the milk along with the water, as one does for chai. This means that everything goes into the thermos at just under 212F/100C, rather than boiling water plus cold milk resulting in a nice cool thermos of bacteria. Doing this changes the taste of the tea slightly, but then so does leaving it in a thermos all day.

And this is part of the answer to this question, as well: You want to maximize the heat at the beginning of the operation, and then consider it safe to drink until the temperature drops into the "danger zone" mentioned above. For example, this Zojirushi thermos is rated at 167F at 6 hours, and at 117F at 24 hours -- meaning that somewhere in the last 14 hours it gets a bit too cold for total safety.

I've always assumed that if it is hot enough to burn my lips, it is hot enough for safety, but that is probably a lot less certain that checking the temperature with a thermometer. I'm comfortable taking that risk for myself, but don't sue me if you get sick, right?
posted by Forktine at 10:06 AM on November 21, 2008

Heh. Forktine has a point. When I worked in food safety, a CDC guy and some health inspectors told a story about going out to eat after a conference. They all had soup, and one of them found a big ol' bug at the bottom of his bowl. They showed it to the mortified owner, who turned pale and nervous when he found out what their jobs were. It became quite awkward, at which point, by way of reassurance, one of them said this: "Well . . . Don't worry too much about it. Even rat poop is fine to eat if you boil it long enough."
posted by averyoldworld at 11:03 AM on November 21, 2008

So, to be specific. I do boil the milk with the tea (as in Chai).
posted by chrisalbon at 12:53 PM on November 21, 2008

Does she like chai? Make that!
posted by flabdablet at 5:22 PM on November 21, 2008

Try freezing the milk in ice cube trays to keep it at a safe temperature for a while longer.
posted by HotPatatta at 5:36 PM on November 21, 2008

Gah, sorry but my eyes somehow skipped over the part of your question explaining how she likes it hot. Does she have access to a microwave at work? There must be a break room in the building. What about a locker or someplace to store a personal item or two? If so, you make it the night before and immediately chill it in the fridge. The amazing thermos will keep it cold and safe for the next 24 hours. She can pour some into a mug at work and microwave it when she's ready to drink it.
posted by HotPatatta at 5:58 PM on November 21, 2008

Tea also has antibacterial properties. Clearly, you need to leave some tea plus milk in a thermos for a day, and then have your wife run a culture on it.
posted by Caviar at 8:03 PM on November 21, 2008

Not to hijack your thread, but what thermos are you using? I'd like to get one for myself, and one that'll keep something hot for that long sounds wonderful.
posted by phaded at 10:54 PM on November 21, 2008

Both of the Zojirushi insulated products I've tried - a glass thermos coffeepot and a stainless airpot - have kept their contents impressively hot for long periods of time. In fact, everything I have made by Zojirushi does whatever job it's supposed to do impressively well. I unhesitatingly recommend their products. They're worth the extra cost over other brands.
posted by Caviar at 9:03 PM on November 25, 2008 [1 favorite]