Ask Jeju: Microwaving Butter

In food on 03/20/2009 at 9:28 pm

The food doctor is in. Leave a comment if you have a question.

A friend of a friend asserts that microwaving butter is bad, but fails to mention why. We had never heard of such a thing. Even Harold McGee does not mention such a warning and he is the master of the food science universe. The resident nerd researched it and has the answers.

Q: Is melting butter in the microwave bad?

Short Answer: No.

Long Answer: Butter is made mostly of milk fats and a little water. If you melt it too fast, the milk solids (i.e. protein, whey, casein) separates from the fats, which is a characteristic taken advantage of by the good people who made ghee. In that case, the water evaporates. A microwave is supposed to cook things evenly (even though there’s ‘cold’ spots), so melting butter in there should theoretically be more efficient and accurate.

America’s Test Kitchen mentions that melted butter can make cakes taste greasy and inhibit rising, which is why most cakes and cookies call for creaming the butter with the sugar, not melting and then mixing, resulting in a poofier cake. Pound cakes, which are denser, can use melted butter if you use a food processor, and that also remedies the possibility of curdled batter.

Then there’s the fear of harmful effects of the actual melted butter process. Free radicals are molecules generated from many reactions in the body and can be created in foods from a combination of oxygen and light or heat that react with a donor molecule.  Think of it as a tiny beebee ripping holes in your skin. But that’s the same thing happens when you get a tan from the sun’s rays baking it.  The light ray actually causes the melanin in your cell to activate and darken.

The donor molecule in foods is polyunsaturated fats because they have lots of double bonds that can accept a free-range oxygen and form a radical. This just means the molecule becomes unbalanced and agitated. It wants to make friends with another atom to be happy and stable again.

Butter contain small amounts of unsaturated fats, but mostly saturated fats, a ratio of 1:2.  Margarine has a ratio of 3:1, giving it a higher likelihood for dangerous effects. For this reason, free radicals in butter can be formed when it’s zapped in the microwave.  And when you open that microwave door, zoom, zap, pow, they smash into your face and rip it into microscopic shreds.

But check this out. When you heat the butter past melting, until water starts evaporating, the over-heating of the milk solids can generate anti-oxidant compounds, molecules that neutralize free radicals. Saturated fats inherently resist breakdown under heat, so that protects them as well.

Incidentally, free radicals are also our friends. In order to kill bacteria that invade our bodies every millisecond, our cells make free radicals in the cytoplasm and use them as bullets to pierce bacterial cell membranes, then quickly neutralize them with innate anti-oxidants. It’s all in a day’s work at the ol’ body garbage dump and recycling center.

Conclusion: the risk of harm associated with microwaving butter from free radicals is extremely low.

Q: But how does a microwave work and how does it affect the butter?

A: Food in a microwave absorbs radio waves, and the energy translates into atomic motion, which, when really really fast, gives off energy in the form of heat. So the heat from within the food particles cook themselves. The water in solid butter would heat up first, given that fat is denser, thereby melting the fat with the hot water bits.

If you overheat the butter, it could over-oxidize, changing the flavor profile by making it taste acrid or bitter. But keep in mind rancid butter could happen on the stovetop as well. Just keep an eye on it.

There are stories/urban myths circulating about how butter-flavored popcorn could lead to lung cancer by excessive continuous inhalation of the fake butter fumes. But as the food doctor knows, almost anything foreign breathed in repeatedly for many years is the pathophysiology of lung cancer. Which is why everything in moderation is the key to good health.

Q: What about just warming the butter in the microwave, to soften it?

A: It’s fine as long as you are patient and put the microwave on low power. We prefer to use our surface warmer on our electric stovetop. It’s the only thing that’s good about having a non-gas range. Okay, now let’s go bake a cake.

the food doctor elaborates

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