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Subject: Re: Tea and milk
My memory (CERTAINLY suspect) of such things is that it's about heat exchange.
Like with acid and water: You always put acid into water because of the heat generated. Acid drizzling into water raises the temperature slowly (as a little acid reacts with lots of water), letting everybody get cozy with each other so the heat of the mixture rises on-catastrophically. If you drizzle water into acid, you get a lot of acid molecules wanting to dance with a few water molecules, causing a bar fight. The heat spikes, the mixture boils and leaps out of the test tube and starts to boogie down with your lab partner.
Like eggs in custard: When you add eggs to a hot liquid you add a bit of the hot stuff (near-boiling cream and tasty bits) to the cool (eggs) first, to get the eggs used to the idea. Otherwise, you tend to get scrambled eggs. It's called 'tempering'.
So: Putting the cool to cold milk into the cup and then adding the hot ouch hot hot hot tea, you raise the temperature of the milk gradually (on a teacup scale, both spatially and chronologically), letting it... uhhh... warm up to the idea of changing temperature.
(Again, this is a distant memory of my Aunt Sadie, who finally gave up on trying to teach Mamma to make a decent pot of tea and concentrated on me, coupled with Papa who knew more things about more things than anybody I've ever known...)
You see, the process of homogenization takes the cute, pudgy, lumpy bits of butterfat in the milk and reduces their size and distributes it pretty evenly through the liquid component of the milk, forming a colloid.
This colloid can be ganked by 1) freezing, and (more important to our discussion) 2) over heating. That's why it's pasteurized (heated to about 145 degrees F for 30 minutes or so to kill the nasty, dreadful beasties in the milk) first, then homogenized (vague memory of a cub scout milk plant tour).
Adding the milk to the hot ouch hot hot hot tea can shock it out of its colloid state (well - SOME anyhow) causing a number of results, many of which are neither aesthetic, tasty nor desirable. Ever see a cup of tea with what looks like an oil spill on the top?
It's got the damaged colloid blues.
Last Edited: 08/27/2010