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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? |
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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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AFAIK the ISO standard is not for enjoying tea, but for "tasting" it. Most people don't brew their black tea that long Most commercial teas are in a fine grind state (fannings) and should not be brewed with 95°C+ water for longer than 2 minutes or bitter tastes will become apparent Whole leaf black tea can be brewed with 95°C+ water for more than 3 minutes to get full flavour Tea has little bio absorb-able caffeine in it, from 10mg to 70mg, many in the range 20mg to 40mg Normal brewing gets most of the caffeine out As I understand it, medically you need 100mg+ to get a physiological dose (an effect) A cup of coffee is 100mg to 200mg of caffeine So if you want caffeine drink coffee |
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In case you're looking for a scientific approach, this paper has some plots showing the amount of caffeine extracted as a function of temperature and time. Look for the "CA" label in figures 2-5. They steep the bags for 30 seconds at a time and record the relative & cumulative amounts of caffeine (and other ingredients) extracted from the tea. |
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The stimulating quality of tea is due more to Theobromine. I read once on my English tea packet about 'stimulating' versus 'calming' brews being dependent upon length of brewing time. This seems to bare that out: http://nobleharbor.com/tea/caffiene.html Personally, 1 bag for 1 cup at 3min is too strong. Instead of reducing brewing time, I increase water by a half cup (stays hotter that way too), getting the full-flavor out of the leaves. |
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You can make a quick cup of "decaf" tea, by letting the bag steep for under a minute, pouring off the water, then pouring more water over it and letting it steep again. The poured off water will contain about 80% of the caffeine. link So you're probably not going to get a lot more caffeine from a longer steep time. |
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