system
Given the following post, respond as if you're commenting on Reddit:
human
Why does tea taste different when adding the milk before brewing compared to after brewing?

I make my tea by adding freshly boiled hot water to a Twinings (other brands are available) Earl Grey tea bag. I usually leave this for about three minutes before taking the tea bag out, adding a small amount of milk, and stirring. Recently I tried adding the milk to the mug first, then the teabag and, lastly, the water. I found the resulting flavour to be distinctively different (a sharper, more fruity flavour, which I prefer but this is completely subjective. All I am worried about is the objective difference in flavour).

Since then I have tried brewing several mugs of tea using both "milking" methods and leaving them to brew for exactly three minutes (timed). I have even tried two blind experiments with my partner to confirm that the difference was not a placebo effect.

I can't think of any reason why the two methods of making tea result in significantly different flavours.
gpt
Milk is an emulsion of proteins and fats (depending on what grade of milk you use), and like any emulsion, it requires some surfactancy to stablize it.  

This is the same way that soap dissolves oils, and it is why milk is white, the emulsion particles are large enough so that visible light is defracted.  If you let milk dry out, it dries clear, so the composition of milk is not inherently opaque. 

Anyhow, by adding the milk first you are adding a surfactant to the tea, and this can help extract favor components, which are often non-polar in nature, out of the tea leaves.  The added stability of the non-polar flavor compounds in water shifts the equilibrium position between the leaves and the water as well, leading to more flavor being extracted.  More flavor gives stronger flavor (seems obvious eh?) Also, by complexing the non-polar molecules you change the way they settle on your tongue, which affects the flavor you experience, this is similar to eating very spicy food, to "cool off" your tongue it's best to drink milk rather than water because the milk will dissolve the oils that give the hotness better than plain water.

Now, of course, this is really subtle, but we're not talking about huge flavor changes, it still generally tastes like tea with milk.  

Why doesn't this occur when you add the milk last?  Generally speaking, the milk is added after you have removed the tea bag, so there is no interaction between the tea leaves and the milk proteins, and therefore no change to the extraction quality, you only get the flavor chemicals that naturally equilibriate into hot water. 

TLDR; Milk has natural soap in it which dissolves the flavors out better.