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Ask the researchers

Why does beer sometimes freeze when it is taken out of the freezer? (Natalia Zapella, via e-mail)

EDUARDO CESARMany people have experienced the frustration of taking a beer from the freezer and seeing it go solid right in front of them. To avoid this, many pick up the beer by its end or put it under running water, only then giving it a shake. To figure out what to do, you just have to understand the physics behind the incident. The beer in the freezer cools down little by little and if the refrigerator does not vibrate, it may reach a temperature lower than freezing. Being static inside the freezer, the molecules lack the orientation to become solid. “It’s as if one had a battalion that needs to be told by its commander to stand to attention,” compares the physicist Luis Carlos de Menezes. What indicates the alignment to the molecules is the abrupt movement of taking the beer out of the freezer, aggravated by one’s worry about having left the beer in there for too long. “The gesture or the warmth of the hand provides this direction,” he explained. As a result, the liquid expands, since the solid state takes up more space than the liquid state, so that sometimes the bottle (or can) will explode. To drink a heavily chilled but liquid beer, it is best to take it out of the freezer without shaking it in any way or touching it with one’s open hand and to place it on a stable surface until it reaches a temperature that is higher than its freezing point.

Luís Carlos de Menezes
University of São Paulo (USP)

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