How does the process of making liquid coffee out of the beans work in a coffee machine? How does it extract coffee/caffeine out of it?


How does the process of making liquid coffee out of the beans work in a coffee machine? How does it extract coffee/caffeine out of it?

In: Chemistry

Beans are usually pre-roasted and sometimes pre-ground. The grounds are soaked in hot water, where the flavor and color compounds and caffeine diffuse out of the grounds and into the water. The flavored, colored, and caffeinated water is filtered to remove the grounds, then served with creamer, sugar, and whatever other additions are desired.

You can make coffee by soaking ground up coffee beans in hot water for 5 minutes, and then pouring the mixture through a fine sieve (that’s how a French press works.) The hot water absorbs the flavour, oils, and caffeine from the beans.

Your Mr. Coffee or other coffee maker is just accelerating the process. Rather than infusing the beans with water, it is just pouring boiling water over the beans in a steady stream. The water then passes through a filter (either a paper filter or a mesh filter) on its way into the pot.

Hot water liquifies the oils suspended within the coffee beans, mixing them into solution with the water.

Without getting too technical, the beans start with 100% of their coffee juices, which equalizes within the water. If you use 10x the volume of water as there are beans, and mix them perfectly, the beans you extract will have 10% of their original coffee juices remaining. That’s how you can get away with re-using grounds to milk every bit out as you can.

The mixing is the tricky bit. Coffee oils can only mix as fast as they can seep through the beans. That’s a function of surface area. Technically, you can make coffee from the whole beans, but they’re going to need a long time to soak. Grinding means there’s lots of surface area, so it mixes readily. You just need some kind of filter for the chunks, or develop a taste for coffee you can chew.

Downside here is that the oils will react with water in the air around them too, so once ground, the good coffee juices are going to start escaping into the air and not your cup, so it’s best to grind them just before making your cup.

You can increase the rate of spread by thinning out the coffee oils with heat. However, if the water’s too hot, it chemically changes some of the good juices, altering their flavor and potential ‘pharmaceutical’ effects. That’s where roasting can be really good for flavor, at a minimal expense to the bean’s chemistry.

But the hotter the water, the faster it mixes. Conversely, you can minimize damage to the chemical composition by letting the bean soak in cold water while the oils slowly separate from the beans. That’s why cold brew coffee is usually way stronger than normal, because it’s chemical makeup hasn’t been modified due to heat. You’re just going to be waiting a few hours while everything mixes.