Caffeine content of cold-brewed coffee: higher or lower than hot-brewed?

Question

I recently rediscovered the joys of cold-brewing coffee. (One level cup of rough-ground beans, 4-1/2 cups of cold water, steeped overnight and strained, produces a rich coffee concentrate. A shot or three of concentrate in a mug topped with hot water makes a cup of coffee; poured over ice and milk makes a fantastic iced coffee drink.)

The information I've found online is contradictory. One site says this method produces a drink with less caffeine than traditional hot-brewed coffee; another says it actually contains more caffeine.

On the one hand, there's the heat in the traditional method. On the other hand, the beans are in contact with the water for twelve hours in the cold method. It seems as if the caffeine content could be identical? While the beans used will, of course, alter the outcome, does anyone know for certain if cold-brewed coffee has more or less caffeine than hot-brewed?

Answer

According to the Wikipedia article on caffeine, its solubility is drastically different between room temperature and boiling (2.17 g/100 ml room temperature to 67g/ml at boiling). I assume this means it's easier to get caffeine into boiling rather than cold water, but the drastically longer steeping time may counteract this. It's worth noting that the solubility is far higher than the actual amounts of caffeine that's in coffee.

Farther down the page it mentions caffeine per liter of liquids like coffee (386-652 mg/l or ~.0004 to .00065 g/ml). If you can find similar information about cold-steeped coffee, it might help.

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