Well, it’s scientifically proven that adding the milk at different points changes the flavour – whether or not that’s for the better is down to personal preference i guess.
If u pour in hot tea, then add the milk, in the first portion of milk the proteins become denatured (effectively cooked – when cooking meat, eggs, or anything, all u r doing is denaturing proteins by changing their chemical structure). O.T.O.H. if u add tea to cold milk, far less proteins are denatured as none of them are in contact with boiling water at any point. Flavour is down to preference (i.e. some people want steak rare, others well-done, it depends how many proteins u want denatured!)
Another interesting (or not…?) point is if u r in a hurry and u want it at a good drinking temp, should u add the milk before or after? This time, u add it after. so u have to have a balance, do u want a quicker cuppa by adding milk after, or one with less denatured proteins?
Read Hervé This’s ‘Molecular Gastronomy’ – all sorts of good food questions. In there he states “For 200ml of boiling tea that is cooled initially with 2.5oz of room temp. milk, a comfortable drinking temp of 55oC (131oF) is obtained after about 10 minutes, but if one waits for the coffee to reach 75oC before adding milk, one obtains the same result in only four minutes. Knowing an elementary law of physics reduces the wait by more than half.”
He also goes on to explain about blowing, stirring, leaving a spoon in, putting in sugar, and what effects these have on tea and coffee.
1. Blowing is more effective than stirring “The same coffee that loses 6oC per minute when one blows on it cools down by 3.5oC when stirred. Experiment shows that a boiling liquid…cools by 11oC per minute when one stirs and blows at the same time [because the temp of liquid is uniform throughout, the surface area greater, etc etc.]”
2. “We will see the effect of a teaspoon in virtually nil: When one takes 2 cups containing coffee at an initial temp of 100oC and puts a teaspoon in one of them, the difference in temperature after ten minutes is less than 1oC. A teaspoon is not an efficient radiator, even when made of silver”
3. The effect of sugar “as predicted by Hawking is too weak to be observed.”
And so on….