add the milk to tea now or later?

The dilemma is this: the telephone range as I was making tea. Should I add the milk now or 5 minutes later, after I took the call? One way of answering this is to make a guess and hope you’re right. Another is to deal with it scientifically and do an experiment.

What I did
I got a couple of cups, two egg-cups of milk and boiled the kettle. I got my data logger and two temperature sensors plugged in and recording.
Next I poured hot water into the cups and added milk to one of them. About five minutes later I added the milk to the second cup and took temperature readings for a few more minutes. Finally, I transferred the readings to the computer. I did not stir the cups at any point.

My results
You will find some of the following questions easier if you put these results into your data logging software. Click here to get the results to import in your data logging program.

My results
You will find some of the following questions easier if you put these results into your data logging software. Click here to get the results to import in your data logging program.

Looking at the results

Use the graph to work out the time when I added the hot water to the cups
At what time did I add the milk to the first cup?
At what time did I add the milk to the second cup?
Which graph line shows the cup where I added the milk after a call?

Look back at the problem. Would it be better to add the milk before, or after the call?
Take readings from the graph to see how much of a temperature difference this makes? What do you think? Was it worth the trouble?

Do you think I should have stirred the cups?

As a good kitchen scientist, I made sure the experiment was done very scientifically. List things that I must have done that I didn’t tell you about.

Would it be better to pour the water from the kettle before, or after taking the call?

Which cools faster in the fridge, a warm bowl of jelly or a hot bowl of jelly?