# UKC

## / boiling a kettle 2

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two cups of tea, same volume of liquids added, same shape cup etc. even the same brand of tea bag.
cup 1 = boiling water added left to brew about 3.75 minutes - i'm a wimpy southerner, milk added.
Cup 2 = boiling water and milk added at the same time or thereabouts. left for 3.75 minutes.

which one will be warmer at point of drinking? i think it will be cup 1, but that's only from a theoretical physicists thought experiment type of view.
adding the milk immediately will give a smaller surface area to volume ratio, leading to less heat loss and a warmer cuppa. however, that assumes the milk comes out of the fridge when poured.

if the milk is taken out of the fridge at the same time in both scenarios, then the problem is influenced by the milk carton too.
> two cups of tea, same volume of liquids added, same shape cup etc. even the same brand of tea bag.
> cup 1 = boiling water added left to brew about 3.75 minutes - i'm a wimpy southerner, milk added.
> Cup 2 = boiling water and milk added at the same time or thereabouts. left for 3.75 minutes.
>
> which one will be warmer at point of drinking? i think it will be cup 1, but that's only from a theoretical physicists thought experiment type of view.

Wrong. And that's from a theoretical physicist point of view.

In reply to foxjerk: OK, rule no 1 when making tea: never put milk into cup first or at same time, as the tea needs boiling water to "brew" for an amount of time. it's the same principle when grandmother using tea leaves would "warm the pot" first.

Cup 2 will be warmer at drinking. When the liquid is hotter (ie. cup 1) there is a larger temperature difference between the liquid and the ambient air temperature meaning heat will be lost faster. Reducing the temp' early on (cup 2) reduces the differential and reduces the rate heat is lost.

For example, in 20 degree C air, water in a cup will cool from 100 to 80 degrees faster than it will cool from 80 to 60.

But, tea should brew at a higher temperature or it won't taste as good, so if you're concerned about drinking temperature and taste, pre heat the cup first, brew, then add milk.
In reply to thomb: ...though adding the milk reduces the temperature at the point of addition; and the amount of reduction won't necessarily be identical.

But theoretical reasoning is, though interesting, of little value when empirical evidence can be easily obtained by those so minded.

T.
In reply to Pursued by a bear:
> But theoretical reasoning is, though interesting, of little value when empirical evidence can be easily obtained by those so minded.

Empirical evidence will confirm that the correct theoretical reason is, well, correct and that the OP is wrong.

That was my initial judgement too.
In reply to foxjerk: I was thinking cup in cup 1 would heat up more than cup in cup 2 providing some better insulation later in the brew. Obviously this would be greater heat loss initially but may pay off later on. Gonna try this tomorrow tea break!
> (In reply to foxjerk) OK, rule no 1 when making tea: never put milk into cup first or at same time, as the tea needs boiling water to "brew" for an amount of time. it's the same principle when grandmother using tea leaves would "warm the pot" first.

But milk in first (assuming a tea bag) has the following advantages:

-No risk of overspill upon adding milk after brewing.

-Bag can be left in till desired browness reached.

-No need to stir.

Indeed, with this last one, if you pour the water on the bag right, it'll stay floating and you don't even need a spoon.
Time at university well spent.
In reply to foxjerk: For all those interested in the best time to put your milk in. http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/-0c2ee7e805/

In reply to foxjerk: Tea should be make in a teapot with boiling water and proper tea (rather than teabags), then allowed to brew.

Add milk to the cup before the tea, this prevents curdling and also protects your fine china from cracking when the hot tea is added.
(or preferably drink it black!)

After pouring your tea add more hot water to the teapot and cover with a teacosy, this will continue to brew and leave you with enough for a second cup of tea without wasting energy reboiling the kettle or having to use a further teabag.

In reply to foxjerk: All is irrelevant unless said brown brew is accompanied by caramel hobnob.
In reply to TheDrunkenBakers: oh course!
In reply to Jenny C: point to note Jenny. You can always tell the class of someone by how they make tea. Those who add milk before water are used to pottery which can crack as it's not as heat resistant. Those who add milk after water are used to china which is heat resistant. A bit like upstairs downstairs. Oh by the way, the easy way to check which is more efficient for any situation with the kettle is simply to turn off every load in the house and count rotations on lecky meter. We often used a kettle to check meters at Scottish power. As it had a 3kw load. Hence the need for the old kettle rocket in kitchen pre modern rewires. If you can get an induction coil test kit to go round the kettle flex it will allow you to do the same with the lights on and maintain ambient temp. Sandy

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