Water vs olive oil when sautéing

In terms of sautéing, the simple answer is that using oil is going to let you develop fond, i.e. the tasty brown stuff, on your veggies whereas cooking only with water will essentially boil/steam your vegetables — and perhaps give them a little char, as well.

In cooking, both oil and water are basically just things you use to transfer heat to food. They are both useful in their own way, depending on what you're cooking.

In practical terms, oils/fats can serve a couple other purposes, too, like:

• Help extract fat-soluble flavor compounds from ingredients, like herbs and aromatics.
• Keep things from sticking and burning in your pan.
• Add flavor.

In a hot pan with only water, your friend was probably boiling/steaming their vegetables — not truly sautéing, in which you really try to avoid steaming. If the water runs low, you risk burning your veggies when they come in direct contact with the hot metal of the pan.

This isn't necessarily a bad thing; it depends on what the food is and how you're trying to prepare it. There are better ways to steam veggies, but hey, whatever floats your boat.

Cooking for Engineers has an illuminating article on the science behind heat transfer. Learning about the Maillard reaction is also a good read. And others more experienced than myself can tell you a lot more, I'm sure. Hopefully this is a sufficient "short" answer.

As I believe has been mentioned in other posts, you really can't saute in water. Saute literally mean to fry in fat. Some vegetables which have a high fat content may saute a little in their own oils if very little water is in the pan, but it is more of a steaming process. The big difference is the amount of heat being used to cook the veg. Olive oils, at least unrefined EVOO start to smoke and burn at faily low temps 200-250 F. Refined olive oils can take more heat, but many cooks like to use high smoke point oils too fry or even saute.

Anyway, using water in the pan keeps the pan temperature fairly low, generally around the boiling point of the water (212 F). You can get it hotter using little water but the water will evaporate quickly and burning may occur. If you add more water, you continually cool the pan inhibiting the mailliard effect. This is the brownig effect that occurs on food when exposed to high heat. This creates a great flavor on most foods.

While there's nothing wrong with cooking in water, the results are quite different from cooking in oil.