How do they get caffeine out in decaffeinated coffee?

Question

Coffee beans naturally contain caffeine. At the store or in a restaurant, you can choose "decaffeinated coffee".

Is really all the caffeine gone or is there just a smaller amount? How do they remove the caffeine from the beans?

Asked by Mien

Answer

The most commonly used method is the Swiss Water Process:

• A batch of unroasted beans is soaked in hot water. Caffeine is water soluble, so it's extracted from the beans. However, some of the other substances that give coffee its flavour ("coffee solids") are also water-soluble and are also extracted.
• The first batch of beans is discarded and the caffeine is filtered out of the water/caffeine/coffee solids mixture by a carbon filter.
• Another batch of unroasted beans is added to the hot water/coffee solids mixture. The water is already saturated with coffee solids, so only the caffeine is extracted from this batch of beans.
• The now-decaffeinated beans are removed, the water/caffeine/coffee solids mixture is filtered again to remove the caffeine and the process can be repeated with another batch of beans or the same batch to remove even more caffeine.

There's no universal definition of "Decaf," but it generally means beans that have had at least 97% of the caffeine (by weight) removed.

Answered by Ward

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Does brewing tea for longer result in higher caffeine content?

Question

The ISO standard for brewing tea says "6 minutes". Of course different teas have vastly different properties, but...

For "average commodity black tea" and "average commodity green tea", will leaving the tea bag in longer (say 1 hour or 1 day) result in higher caffeine content in the cup? How much?

Answer

First off, the ISO standard is not intended to produce a good cup of tea. It is designed to produce a consistent one for taste testing, so that no tea manufacturer can claim that his tea wasn't made "properly". It's title is "Tea -- Preparation of liquor for use in sensory tests"

As for the actual tea making, yes, leaving the bag in longer will make a stronger cup of tea. The concentration of caffeine (along with flavour molecules and everything else) will slowly trend towards an equal concentration in the leaf and in the water. The longer you leave the tea bag/leaves in the water, the closer to equilibrium you will get.

There are other factors that affect this, such as the temperature of the water, cut of the leaves, bag versus loose leaf and so on, but the trend is always towards equilibrium as time progresses.

I'm not sure where the upper limit of this lies, but I think that once the cup is cold there's no point in it anyway. Thus, leaving the bag in for an hour is a bit much. I usually steep my tea for 3-6 minutes, depending on how strong I want it to be.

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Which Type of Japanese Green Tea Has the Highest Amount of Caffeine?

Question

I am trying to find the best pick-me-up Japanese green tea and was wondering which type was the best to get from the assortment of Sencha, Gyokuro, Kabusecha, Bancha, etc.

Answer

From what I've read, caffeine content can be variable even within varieties. There are possibly seasonal variations, variations in harvesting and processing technique, variations in the original plants... Psychological effects (e.g. what smells perky to you) might be just as strong, and steeping for 10 minutes instead of 5 might make as much difference as any choice of variant. So take any answer with a grain of salt, and don't be afraid to simply go with what seems to subjectively work best for you.

That said, gyokuro is supposed to be stronger than other sencha teas, and I believe compared to other Japanese green teas as well. (I found similar information elsewhere; it's not just wikipedia.)

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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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