I have observed a strange phenomenon. I my mouth is very sensitive to very hot liquids (like, freshly made tea, or just freshly boiled water), so when I make my tea, I usually wait around 20 minutes before drinking it.

I am also a fan of a particular 3 in 1 instant coffee (3 in 1 meaning instant coffe + instant milk + sugar). I am taking one pack of mentioned coffee (21 grams in one package), pouring it with with freshly boiled water, mixing the coffee with water using a teaspoon in room-temperatured cup, then I am going to the toilet for ~5-7 minutes. When I come back from the toilet, my coffee is ready to drink. It is hottish, but I can drink it right away.

Later on (2-3 hours later), I am making a cup of tea, using the same cup, which is in the room temperature again. I am pouring two teabags (4 grams of tea) with the same amount of freshly boiled water, and I make my breakfast. It usually takes me around 10 minutes to make my breakfast, and when I am trying to drink my tea right after finishing making by breakfast, it is still hot as hell. I am usually waiting another 10 minutes, then the tea is still hotter than the coffee after 7 minutes, but it starts being acceptable for my sensitive mouth.

I have even bought a food thermometer to check the cooling speed of both liquids, but because of the coronavirus outbreak it hasn't arrived yet, but my "internal" thermometer - my lips, and isides of my mouth cannot be wrong. I can drink the coffee after ~7 minutes, and the tea after ~20.

I would understand a little change in cooling time, cause we are talking about 21 grams of instant coffee-sugar-powdered mix, the liquid is a bit densier, maybe there is more energy used to dissolve the coffee ingredients, the instant milk contains fat, but still - i am talking here about 13 minutes of difference between the time when my mouth can accept the temperature of both liquids, and we have to remember that the tea is still a hotter 20 minutes after I pour it with boiling water than the coffee 7 minutes, but it is drinkable.

Is there an explaination for this?

  • $\begingroup$ You might find this interesting: en.m.wikipedia.org/wiki/Lady_tasting_tea (Ronald Fisher is one of the founding fathers of the modern statistics) $\endgroup$ – Vadim Apr 5 '20 at 10:42
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    $\begingroup$ I have even bought a food thermometer to check the cooling speed of both liquids A thermometer is key here. Do your measurements and then get back to us. $\endgroup$ – Gert Apr 5 '20 at 12:29
  • $\begingroup$ Coffee is stirred while tea isn't - if I'm understanding well the question. That might help cool the coffee. $\endgroup$ – Pere Dec 30 '20 at 14:15

I can think of two possible differences which might contribute this result, but I am not sure how you could test them. The different composition of the drinks will affect the surface tension. This could affect the rate of evaporation of the liquid. If this is the case, it may make a substantial difference to the rate of cooling as evaporation is probably the greatest cause of loss of temperature.

The other cooling effect which will be different is radiation. Do you add milk to your tea? If the coffee is darker than the tea, it will radiate faster and cool faster for that reason.

If you don't add milk, the tea will be translucent. I am not exactly sure how that will affect things, because it means that radiation is possible from the interior, not just the surface. Also it may not be translucent for the wavelengths radiated. But generally, I think a translucent substance will radiate much less.

  • $\begingroup$ My guess is that the OP doesn't add milk to their tea, or they'd mention it, since they did say: "the instant milk contains fat" in relation to the coffee. $\endgroup$ – PM 2Ring Apr 6 '20 at 7:14

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