A question for Phys...
 

[Closed] A question for Physicists and Tea Drinkers

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So, I make a cup of tea, take out the teabag, and leave it for 5 minutes. I come back, add milk and drink it.
Alternatively, I make the tea, add the milk and [i]then[/i] leave it for 5 minutes.

Which one will cool the quickest?


 
Posted : 03/05/2010 5:22 pm
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the first - rate of cooling depends on difference between tea and ambient and 1st option is hottest to begin with

IANAphysicist


 
Posted : 03/05/2010 5:24 pm
 Rio
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Assuming your milk is cold, the first one will cool most - see Newton's Law of Cooling for more details.


 
Posted : 03/05/2010 5:25 pm
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mind, you're supposed to add the tea to the milk to prevent scalded milk aren't you ?

(so my nana used to say)


 
Posted : 03/05/2010 5:28 pm
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If I were making a Pot of tea, I'd always put the milk in the cup first, however as I'm a lazy student it normally comes down to a teabag and the milk goes in after


 
Posted : 03/05/2010 5:30 pm
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You've got to consider the properties of the cup though. The first will heat the cup up to a higer temp and this will make all the difference.. I'll go for option 2.


 
Posted : 03/05/2010 5:31 pm
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Put the milk in first, even with a teabag - It creates an emulsion rather than a mixture. Mmmmmm


 
Posted : 03/05/2010 5:32 pm
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A far more important question is why on earth would you want to put milk in tea in the first place.


 
Posted : 03/05/2010 5:33 pm
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Leaving aside the "[b]It creates an emulsion rather than a mixture[/b]" nonsense, if you put the milk in first with a tea bag the mixture temp will be too low to brew properly.


 
Posted : 03/05/2010 5:38 pm
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I would say that the tea needs to come into contact with freshly boiled water to get the brewing going, so like johnners said, you cant let the tea bag touch the cold milk first


 
Posted : 03/05/2010 5:40 pm
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but how could a cuppa tea ever last longer than 5 minutes?


 
Posted : 03/05/2010 5:40 pm
 CHB
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johnners is right. With teabags you must add milk after if making in a cup. The tea will not infuse properly otherwise. JAM29er you are talking crap, milk is a water based colloidal suspension, so mixes with other water based systems just fine.


 
Posted : 03/05/2010 5:57 pm
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For 20cl of boiling coffee that is cooled initially with 7.5cl of room temperature milk, a comfortable drinking temperature of 55Celcius is obtained after about 10 minutes.
If one waits for the coffee to reach 75celcius before adding the milk, one obtains the same result after only 4 minutes.

[url= http://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law ]Due to Stefans law.
[/url]
Covered in detail in the book Molecular Gastronomy: Exploring the Science of Flavour by Herve This...


 
Posted : 03/05/2010 6:05 pm
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JAM29er you are talking crap

I meant solution, not mixture - otherwise I stand by it. You don't need boiling water for tea to brew properly unless it's fruit tea or black tea. For green or white tea (wot us plebs drink) 70 degrees centigrade is more like an ideal brewing temp. For black tea (Assam etc) this may not work


 
Posted : 03/05/2010 6:07 pm
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More to the point milk is homongenised, back in the day heat could disturb this and bring the fat out of suspension.


 
Posted : 03/05/2010 6:07 pm
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Ciarán - Member

For 20cl of boiling coffee that is cooled initially with 7.5cl of room temperature milk, a comfortable drinking temperature of 55Celcius is obtained after about 10 minutes.
If one waits for the coffee to reach 75celcius before adding the milk, one obtains the same result after only 4 minutes.

Due to Stefans law.

Covered in detail in the book Molecular Gastronomy: Exploring the Science of Flavour by Herve This...

What are you on??? No-one mentioned coffee!!!


 
Posted : 03/05/2010 6:13 pm
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We all know that tea with milk tastes different depending on whether you put the milk in first or second - personally, I think it tastes 'smoother' milk first, but prefer milk second.

However, after much rigorous testing and evaluation, I have concluded that if you take a cup of tea with milk added second, leave it to cool, then reheat it in the microwave, [i]it then takes on the smoother taste of tea with milk added first[/i][i]![/i]
Go on, try it yourselves, you know you want to. 🙂


 
Posted : 03/05/2010 6:19 pm
 CHB
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JAMer29 ordinary tea that comes in teabags is black tea.
Green tea is entirely different taste and should never be taken with milk.
White tea is very rare, and expensive. It is also very subtle in flavour.
Milk is not classed as a solution as most of the constituents (casein and fat) are not disolved, merely suspended.


 
Posted : 03/05/2010 6:25 pm
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I like my [regular] tea weak, with plenty of milk. A strong-brew favouring mate describes it as "Mujahi-tea-n", and is visibly alarmed by both the colour and taste.


 
Posted : 03/05/2010 6:29 pm
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CHB - ordinary tea is normally a 'blend'
- I'll drink what I like how I like, but thankyou
- I didn't say milk was a solution, but that tea with milk added second was.


 
Posted : 03/05/2010 6:41 pm
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our kids at school do this as an experiment using data loggers and temperature probes.
Apparently if you add the milk straight away it cools quicker as there's more of an initial reduction in temperature. so I'm told.....
The thing about putting in milk first then adding tea comes back to the origins of drinking Tea. It used to be very expensive and the upper classes used to use bone china cups, also expensive. Therefore if you put hot tea into the cups you risked cracking them. Put in milk first, then it cooled the hot tea as it was added and protected the bone china cups.
For us plebs who used earthenware mugs, it doesn't matter!
You have to let tea brew though, so putting milk into a cup with a tea bag then adding water doesn't brew it properly, so you don't get all the flavours.
Tea bag+ boiling water, stand for ~2mins, remove bag, add milk.....perfect!
My tuppence!
Q


 
Posted : 03/05/2010 8:28 pm
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People actually use the hotter cools faster technqiue in the real world.
Ice rinks are made with boiling water.

I put the milk in after the tea bag has been brewing for a while. The other way round is crazy, do people put milk in the tea pot? No.


 
Posted : 03/05/2010 8:36 pm
 juan
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People should not put milk in tea... Actually there is a lot that people should not do...
use a tea bag, come on do you really think there is tea inside?
boil the water, black tea is meant to be brewed at 95 C, green tea more between 50 and 80 depending on the type of tea.
wash the teapot, but then you need one teapot per type of tea
leave lime-scale in the kettle (that is just gross)
Put sugar before the tea no no no, you brew it then sweeten it


 
Posted : 03/05/2010 8:43 pm
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I used to always put the milk in first. Mainly because it annoyed my housemate at uni.

Now I add the milk last, because you don't need to stir coffee when doing this and it's carried over into my tea drinking.


 
Posted : 03/05/2010 8:47 pm
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[i]use a tea bag, come on do you really think there is tea inside?[/i]

If it's not tea, what is it?


 
Posted : 03/05/2010 8:53 pm
 Bez
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[i]Which one will cool the quickest? [/i]

During the five minutes you leave it, the one with no milk in will be cooling at a faster rate. But after the total process, ie with milk added in both cases, the one where you added the milk initially will be cooler (unless the milk inhibits evaporation through material rather than thermal means - which, frankly, I doubt and I'm going to ignore).

Reason being that the unmilked one will have a higher temperature difference between it and its surroundings for the five minutes, so loses more heat. The heat contained in the two liquids (ie the heat you add to the system) is exactly the same in both cases.

This assumes: your tea is hotter than the surroundings, your milk is colder than the surroundings, and the milk added in each cup is at the same temperature (ie you didn't leave it warming up in the one where you added it afterwards).


 
Posted : 03/05/2010 9:02 pm
 juan
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If it's not tea, what is it?

Caca... Tea are what you get at the top of the straining process at the tea plant, nice leaves. Tea bags are what you get at the end, so basically dust, made of any possible rubbish.


 
Posted : 03/05/2010 9:16 pm