The Gastronomer

Spuds, an Open and Shut Case

By Andreas Viestad
Special to The Washington Post
Wednesday, July 9, 2008; Page F01

Food science has made many advances in the past few decades, but the progress has been uneven.

We know how to make stable foams, for instance, and why a mayonnaise behaves as it does. I once met a scientist who took MRI scans of foods, from celery to meatballs to porridge, to find out how they look from within. I met another who had won the humorously prestigious Ig Nobel Prize for his research on dipping biscuits in tea and dunking doughnuts. A good friend of mine is the first man to have measured the pressure inside a souffle.

They are performing tasks both large and small that, as all good research should, raise the level in our common pool of knowledge.

But some of the simplest mysteries of cooking remain unsolved. Like putting together a simple potato salad. We may know how to make a fairly good one from new potatoes, flavored with the inspiration we get from a warm summer breeze. But we still didn't know what really happens when potatoes meet dressing or why most recipes ask us to toss the potatoes with the dressing while they are still hot. What does that contribute, apart from increasing the risk that we'll burn our fingers?

Until recently, no one had bothered to investigate this fairly basic issue. It is not the question on which the future of the world hinges, but on lazy summer days, potato salad does feel like an important part of our well-being.

Luckily, some investigators will leave no potato unturned in their search for deeper understanding. Biochemist Rachel Edwards-Stuart is a researcher for the Fat Duck, the avant-garde restaurant outside London, where she is working on developing a dish inspired by the multi-course chewing gum that Willy Wonka served in "Charlie and the Chocolate Factory." Edwards-Stuart is also the world's foremost potato salad researcher; she is finishing a European Union-sponsored project on the subject. The results are clear and the scientific paper is forthcoming, but this is the first time they have been publicized.

"To begin with, my task was simple enough: a project that would take weeks, or a couple of months at the most," Edwards-Stuart says. "I was to test the validity of the claim that one should toss the potatoes with the dressing while the potatoes were still hot. Does it make any difference? We had assumed that it wouldn't matter much. A potato is about 80 percent water, whether hot or cold, and water and oil are not great friends."

But the task ended up being anything but simple. The project would keep her in the lab at the French National Institute for Agricultural Research in Paris for 10 months, tossing hot and cold pieces of potato with oil, analyzing and quantifying the oil intake. And, yes, it turned out that generations of cooks have been right: Hot potatoes do absorb a much greater amount of oil. But the whys and hows were more difficult. And to complicate things, there were significant variations between different samples from the same potatoes. One piece of a potato would absorb a large amount of oil, another much less.

"You wouldn't believe how many different models and explanations we tried out," Edwards-Stuart said. "In the end we landed on this: The cooling of the potatoes happens unevenly. First the outer layer cools and shrinks, while the interior remains hot. Because of this, cracks are formed in the outer layers, and this is where the oil enters. When the potatoes have cooled down, the interior shrinks as well, and the cracks will close."

A few additional findings may also be useful. Even though no single explanation can account for the variation in the results, the structure of the potatoes is important. If you cut through a potato and study it closely (you don't need a microscope, just good eyesight or a magnifying glass), you will notice the central vein system of the potato. Cells in these parts have a different water composition from those in the outer parts, and the researchers think that explains the difference in oil intake among different samples from the same potato.

Another minor finding that didn't come as a surprise: When the oil is heated, it runs thinner, allowing it to penetrate more easily.

Where does all that leave us, as home cooks? How can we use the knowledge from the potato salad research to make our own potato salads better?

"That is really not a question I can answer," Edwards-Stuart says. "I did not study the taste aspect in my research. Unfortunately, we didn't have the sensory facilities to measure the flavor of the potato salad."

That means we have to return to our own labs, the ones we use every day in our lifelong study of what scientists call "the taste aspect": our kitchens. Armed with potatoes, oil, herbs, garlic, lemon, my newfound knowledge and my pre-installed, much-used sensory facilities, I set out to improve on my favorite herb-scented potato salad. I now know that absorption of oil depends on tiny cracks and the capillary system inside the potato. So how about creating more cracks and openings? I decide to prick the potatoes with a needle or a fork before tossing with the oil-based dressing, which seems to increase the absorption even further.

I have always considered my dressing, with its taste of far-too-expensive Ligurian extra virgin olive oil and a generous amount of herbs, to be the strong point of my potato salad. When the potato salad has cooled for a while, all the flavors have blended so that it is hard to tell where the taste of the grassy olive oil ends and the equally fresh and grassy flavor of parsley begins. But the dressing can be improved. By crushing the herbs and garlic so the flavors are released and blended before the dressing is absorbed, I ensure that the flavor that goes inside the potatoes has reached its full potential.

And just to show off the process a little bit, I developed another recipe that involves dipping warm, pricked potatoes in the liquid from pickled beets; when those capillaries absorb the liquid, the potatoes take on a vibrant pink halo.

A small step for mankind, perhaps, but a giant leap for my summer dinners.

Andreas Viestad, author of "Where Flavor Was Born" and co-host of the upcoming public television series "Perfect Day," can be reached at or His Gastronomer column appears monthly.

© 2008 The Washington Post Company