Why when you evaporate coffee and store the steam until it becomes liquid again, the liquid no longer has the color of coffee?



I did this experiment one day because I was curious, sorry if it’s a stupid question

In: Chemistry

Coffee is basically just bits of coffee bean suspended in water. When you evaporate the liquid, only the water is boiled off, and the bean bits get left behind as a sediment. The color of the coffee comes from the beans, ergo if the beans are left behind, so is the coloration.

Because the coffee oils have a higher boiling point than water. So you’re basically distilling the water out of the coffee, and leaving the “coffee” behind.

Evaporating water, collecting the steam, and condensing it back into water is known as distillation. By doing this with coffee, you are essentially just separating the coffee from the water – the coffee stays in the cup and the water turns into steam (that you collect and condense back into water). Because the water no longer has the coffee in it, it goes back to being clear.

The reason that coffee looks brown is because tiny bits of the coffee bean are dissolved in the water. When you evaporate the coffee, only the water evaporates. The boiling point of the coffee bean pieces are WAY higher than the boiling point of the water. That means that you’re left with mostly pure water in the steam with no dissolved coffee.

What you did is called distillation. Basically, you can separate the different parts of a liquid solution by taking advantage of the differing boiling points of its parts.

Water boils at a lower temperature than caffeine and, likely, most of the other stuff in coffee. By heating the coffee up enough to boil the water but not enough to boil that other stuff, the vapor that condenses will be almost entirely water while the rest of the stuff like caffeine will be left behind.

The part that makes coffee that color and makes coffee taste like coffee (coffee beans/grounds) does not evaporate but the water that is used to make the coffee does.

To add on to this question, how small do the coffee particles have to be to become trapped and suspended in the distillation solution? Or will they always be left behind no matter the size?

Your experiment just accidentally invented distillation.

If you have water with stuff in it, when you heat it up, the steam is just pure water. The stuff is left behind when the water evaporates – so when it becomes liquid again, that liquid is just water. You could do this with coffee, tea, juice – or even milk, spaghetti sauce, jam, or yogurt. Anything with water in it. The steam coming off is pure water only.

This effect is why the ocean is so salty. Salt dissolves into rivers and lakes from the ground, and gets carried into the ocean. When the sun evaporates ocean water, the salt is left behind and just accumulates in the ocean.

This can be useful for making drinkable water out of sea water too, just boil or evaporate it and collect the condensation.

You use this effect when cooking every time you “boil down” a sauce or soup to make it thicker. That only happens because it’s not the whole sauce boiling away, it’s only the water *from* the sauce leaving, so the sauce left in the pan gets thicker and more flavourful as you remove water from it.

Because you can’t evaporate coffee. You can only evaporate the water that is in coffee. Evaporation basically separates the coffee from the water and condenses back to liquid as just pure water.

your dirty bean water has tiny bits of beans, it’s really dirty. They don’t evaporate with the water, so the condensated liquid is just water, not the really dirty dirty bean water you want.

In a nut shell you have simple distillation happening. Water vapor is leaving the main liquid source as a gas form, leaving the rest behind. The coffee parts do not become gas so they stay behind. To sum it up, basically there are two parts of the coffee to consider 1. The coffee 2. The water. And the water is the only part that steams. The reason it may smell like coffee is because there are smelly compounds that do evaporate with the water, but the compounds that have color don’t.

Coffee is a mixture of water and other stuff.

Boiling is when you turn a liquid into a gas by making it hot.

When you heat coffee, the temperature where the water becomes gas (steam) is lower than the temperature where the “other stuff’ in the coffee would become gas.

So the gas you create by boiling it is just the water. The “other stuff” stays behind in the pot and wouldn’t boil unless you subjected it to much more heat. (And even then it wouldn’t raise the temperature high enough until after the water finished boiling away first. In a sense, once a liquid reaches the point where it starts to boil, the job of changing that liquid into gas gets “first dibs” on using the heat energy, so the temperature doesn’t go up until that job is done greedily stealing all the heat for itself.)

This is a common method for extracting the pure water from the other stuff it’s been mixed with. For example, this technique can be used to make drinkable water from saltwater, because the salt is part of the “other stuff” that stays behind and doesn’t become steam.

When you have liquid coffee, what you really have is a bunch of little pieces of solid coffee sitting in the liquid water. You cant feel the solid parts because theyre really really small and mixed in really really good. When you heat it up, only the water leaves through the steam, the solid coffee cant go up with it. So when the steam becomes liquid again its just water. You can do this with water you find that may not be safe to drink, since the same process also gets rid of things like sand or dirt that you dont want to drink.

When you boil the water it changes from it’s liquid state to a gas state (steam). The coffee particles, however, do not change state, they stay a solid. The water steam rises by itself leaving the coffee molecules behind, so when you cool it back into a liquid state it is pure water again. This is the same process used for desalination (getting the salt out of salt water).

This works because coffee, salt water, etc are mixtures of two compounds, and so can be separated by physical means.

Steam is made out of water. You didn’t turn the coffee to steam, you turned the water to steam – so when you turn the steam back into liquid, it’s just liquid water, the part that makes it ‘coffee’ gets left behind.

This is the same reason rain isn’t salty even though a lot of clouds are formed from water evaporated from the oceans.

Evaporation is a process of changing the physical state of water (though other liquids can also be evaporated at different temperatures and pressures), so evaporation doesn’t affect the molecules of coffee that are dissolved in the water, just as salt doesn’t evaporate from the sea. You can also see this in cooking, especially if you’re making soup or a sauce. If you keep it hot enough for steam to rise, you can reduce the water in whatever you’re cooking, which makes the result a thicker version of whatever you’re cooking. If you simmer a pot of soup with the lid off for a couple of hours you will see the level fall, but virtually none of the food or seasonings left the pot!

The evaporation process forces water from a liquid into a gas, so even if the water has dissolved material in it (like sugar, salt, or coffee) it isn’t *chemically* bonded, and the molecules of water relatively easy just leave behind the rest of the “stuff” because those solids are not going to change into a gas.

One other way to look at it is to drop a few drops of water onto a hot pan: they quickly boil, sizzle, and evaporate, but they don’t take any of the pan with them, and water can just as easily leave other material behind when it evaporates, even though those dissolved particles – e.g. salt, sugar, or coffee – are much smaller than the big metal pan. This last one is only as helpful as you want it to be, we wouldn’t expect water to “carry” a pan up into the air when it evaporates!

Think of coffee like a powder dissolved in water (I mean, instant coffee is literally this, but it works for bean-brewed coffee in basically the same way). When water boils, it turns into steam, but the little coffee particles are still around in the liquid below, so the two substances separate. Only the water evaporates.

If you actually boil away *all* of the coffee’s water, you will actually be left with all of the brown-colored coffee residue stuck to the bottom of your container (I don’t recommend doing this at home though since once all the water is gone, the heat will quickly transition into burning whatever’s left and that will just be a nightmare to clean up). But you can add water back to it and get something resembling your original coffee again; which is how you get instant coffee mix.

Distillation this and that. Right. Basically, what I’m not seeing on other responses, when water turns to steam it doesn’t really have the ability to pull other things with it into the air. It’s just water. The water in the pot has a bunch of coffee stuff mixed in but when that liquid water turns into a gas, it’s pretty much like the liquid molecules saying “lol, I’m outty” and floating into the air ditching his homies behind. That selfish prick stops holding on to his other water buddies who collectively are holding on to all. The coffee goods. If all the water evaporates, let’s go of each other, and floats into the air leaving everything else that doesn’t evaporate being… you get the result of your experiment.

Different materials have different physical properties. Properties like boiling point. It’s the same principle at play in petroleum distillation. Kerosene vapourizes at a different temperature than gasoline which vapourizes at a different temperature than diesel, etc. They evapourate and rise up a column to a certain height according to that temperature, where they are then sucked away and condensed back into liquid, but purified from their origin in crude oil.

Do that to anything and you get distilled constituents. One constituent (water in this case) evapourates at 100 °C(212 °F). In order to vapourize the constituents in coffee that make it black (really dark brown), it would take considerably more heat. So, heat coffee do only 100 °C, only the water evapourates. The other constituents don’t, and are left behind.

Again, the same principle is at play in how seawater evapourates off the ocean, but it falls as freshwater rain inland. It would be a very different planet if rain was salt water.