Today, we learn why you don't have to put mayonnaise in the refrigerator. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Years ago, in the army, I'd argue with friends in the mess hall. We wanted our coffee to be as warm as possible when we got around to drinking it. Should we put the cream in right away or should we wait. The question was loaded with possibilities.

After all, the cream warms while the coffee cools. Coffee loses heat fastest when it's hottest, before we put cream in. Convection's less effective in creamy liquid -- and so on and on.

To this day I don't know the answer. But, when I left the army I went off to do a Ph.D. in thermal science. Questions -- even seemingly silly questions -- do open doors.

Now I turn pages in a neat little book on rainbows, curve balls and other wonders of the natural world by Ira Flatow. And those long formative conversations come back to me.

Flatow gazes at the colorful multidimensional world around us. He asks us to join in asking how it works. He doesn't organize his questions by scientific field. Instead, he takes us where you and I might really go -- to the beach, the kitchen, the concert hall, the ball park, the bathroom.

That makes his questions plausible. They're questions you might ask -- not ones a scientist would want you to ask.

We walk through the kitchen. We ask about air bubbles lining a water glass that's been left standing. We ask about boiling water -- about the sounds it makes -- about why watched pots don't boil. That's my field, and he's got it right. Maybe he read the book I wrote long after I left that army mess hall.

You see, the processes on your kitchen stove are like the ones in a modern power plant. The mind that questions things around it is the same mind that reshapes things around it. Lessons lurk in questions about microwave ovens, breaking eggs, and cooking meat.

At the beach we ask why waves break and the sky is blue, why rainbows are arcs of a circle. At the ballpark we ask if pitchers really can throw curve balls and why bats have a sweet spot.

I recognize so many of Flatow's questions. They're the same questions that shaped me -- that made me an engineer. They're the questions that'll make your sons and daughters into engineers and chemists -- into artists and mechanics.

Oh yes: Why don't you have to put mayonnaise in the refrigerator? It's because it has vinegar in it. The high acidity kills germs. But, if you make mayonnaise into a salad dressing, you dilute it. Then it's vulnerable to contamination.

So don't leave that salad dressing out.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Flatow, I., RAINBOWS, CURVE BALLS, and Other Wonders of the Natural World Explained. New York: William Morrow and Company, Inc., 1988.

Be careful with your mayonnaise, by the way. It may not grow bacteria outside the refrigerator, but it can go bad without becoming toxic in not too many days. I keep mine in the refrigerator.