Tea and Altitude: the high leaf.
November 21, 2011 3:29 PM   Subscribe

Water in La Paz boils at 80º C. What effect would that have on the taste of tea? Would a La Pazian never get to taste the perfect brew?
posted by omnigut to Food & Drink (19 answers total) 2 users marked this as a favorite
It would taste the same, because the chemicals in tea "boil" at the same adjusted temperatures relative to water. In other words, the tea is at altitude, too.
posted by Cool Papa Bell at 3:35 PM on November 21, 2011

I have had pretty horrible experiences with some weak and tasteless tea at high-altitude huts of the Alps. I would believe that, yes, a La Pazian never gets to taste the perfect brew.
posted by Namlit at 3:40 PM on November 21, 2011

Response by poster: So identical relative boiling points means the flavour will not change? Huh. Thanks!
posted by omnigut at 3:47 PM on November 21, 2011

Different teas require different temperatures to elute the aromatic and flavor compounds from dried leaves.
posted by Blazecock Pileon at 3:49 PM on November 21, 2011

Best answer: To infuse black tea you don't need boiling water. You need water at greater than about 97 °C. If you can't raise the water to that temperature then you can't brew black tea.

I am an astronomer and an Englishman, and I can confirm from bitter (ha!) personal experience that black tea brewed at altitude is disgusting.

If my word isn't good enough for you, then I quote question 7.4 from Second Year Kinetic Theory and Thermodynamics course at the University of Oxford:
Some tea connoisseurs claim that a good cup of tea cannot be brewed with water at a temperature less than 97 °C. Assuming this to be the case, is it possible for an astronomer, working on the summit of Mauna Kea in Hawaii (elevation 4194 m) where the air pressure is 615 mbar, to make a good cup of tea without the aid of a pressure vessel?
and from the answers (omiting the full worked solution in case of Googling Oxford undergrads)
… so that after putting in the numbers, I get the boiling point to be 87.4 °C. The tea up there is dreadful. (I have verified this experimentally.)
posted by caek at 3:55 PM on November 21, 2011 [16 favorites]

Cool Papa Bell: "the chemicals in tea "boil" at the same adjusted temperatures relative to water."

Not quite true - solubility of liquids and solids is more dependent on temperature than pressure. If, for example, the compounds in tea aren't water-soluble unless the temperature is 85°C, then 'boiling' at 80°C isn't going to release them from their existing associations and dissolve them. The tea won't taste like tea.
posted by Pinback at 3:56 PM on November 21, 2011 [2 favorites]

CPB, I am not sure that is essentially correct. In many cases it is not the "boil" but the actual temperature which is important. Kind of akin to how to have to cook things longer at high altitude, the food is not "at altitude" in respect to how done it is.
posted by edgeways at 3:58 PM on November 21, 2011

or.. ah yeah what they said
posted by edgeways at 3:58 PM on November 21, 2011

Right - it's not the volatility of the compounds in tea that allows them to infuse into the water, it's the solubility, which depends more on temperature than pressure. You can put a tea bag in water in a vacuum chamber and boil it all you like - all you'll get is vaguely tea-colored water, as if you had placed a tea bag in a cup of room temperature water on your kitchen counter.

You're never going to have "perfect" tea in La Paz without a pressure cooker.
posted by WasabiFlux at 4:01 PM on November 21, 2011 [1 favorite]

If Cool Papa Bell were right, we could do all liquid-solid extractions at room temperature just by holding a sufficiently hard vacuum over the solution, but this is clearly not the case. And if you think about the physics, it makes sense that Cool Papa Bell cannot be right: we brew tea with hot water for the kinetic effect, so that the tea-like compounds diffuse out of the leaves more quickly. I think CPB may be getting diffusion confused with distillation, where a vacuum does help. In any case, tea will definitely taste different if brewed at 80C.
posted by d. z. wang at 4:02 PM on November 21, 2011

Hmm, on non-preview, I doubt it would be a solubility effect (notice, for example, that iced tea doesn't have any precipitate), but I would be willing to be corrected on that one. I'm still pretty sure it's got nothing to do with pressure, though.
posted by d. z. wang at 4:03 PM on November 21, 2011

You're right, d. z. wang, and I mis-spoke a bit. It's not so much solubility as the energy required to break the existing chemical bonds (simple version: that which sticks the oils and other compounds to the tea leaves) so they can roam wild and free and re-associate with water molecules (in solution), themselves (as a suspension), or vaporise (the smell of tea).

As air pressure goes down, the energy required to boil water is reduced. If the boiling point is low enough, then there won't be enough energy being put into the system to break the original chemical bonds in the tea leaves.
posted by Pinback at 4:16 PM on November 21, 2011

It's probably worth noting that many Paceños (=La Pazians) drink Coca leaf tea, which according to wikipedia is brewed at 70-80º C. Which suggests that they can indeed get a perfect cuppa, just not of black tea.
posted by nomis at 4:21 PM on November 21, 2011 [3 favorites]

Yes, some green teas are intended to be brewed as low as 140F.
posted by rhizome at 4:53 PM on November 21, 2011

Response by poster: Experientially corroborated with caek's answer: we were there, and I wasn't impressed with the results. However, the tea bags were bought in a cheap local store, and called "Cafe Paris", so I didn't want to be too quick to judge the water.
posted by omnigut at 5:20 PM on November 21, 2011

Having lived there, I'd say the quality of the tea itself is a bigger problem than the reduced boiling temperature.
posted by O9scar at 5:44 PM on November 21, 2011

I was about to come in here and suggest adding salt to your water to raise the boiling point, but then I realized that would mean salty tea.
It wasn't very well thought out, I realize.
posted by FirstMateKate at 8:14 PM on November 21, 2011

Heh, I thought you meant La Paz, Mexico (altitude less than 100 feet above sea level). I presume you mean the one in Bolivia.

As a regular tea drinker and connoisseur, I think 90% of the talk about temperatures and boiling points is baloney. I wouldn't be a bit surprised if you could get your tea to taste fine at 80c if you brewed it a bit longer.

The quality of the tea (drugstore bags are not good) and the mineral content of the water have way more effect than temperature in my experience.
posted by mmoncur at 9:02 PM on November 21, 2011

Well, as any experienced tea-drinker knows: black tea: near boiling, green tea: lower temp. So, if I were at altitude, I would brew green tea.
posted by ob at 9:52 AM on November 22, 2011

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