In electric drip coffeemakers, water is pushed up by boiling a portion of it at a time, right?

My friend told me that unless he uses warm of hot water in the coffeemaker tank, the resulting coffee will be much cooler. I find this very hard to believe as I always use cold water and the coffee comes out hot.

All the water will travel past a heating element, and steam "bubbles" will push the water on the top where it will "drip". BUT is it possible that in cheaper coffeemakers the cold water can slip past the heating element un-heated and travel up with the following bubble, cooling down the outcome? Is this where the watts will really come into play?

I am not asking if cold water should be used, but rather if such a scenario is possible. I do not have a precise thermometer or a cheap coffeemaker to test this. Also, I found this very hard question to google, as the only keywords I can think of are "cold, water, drip, coffee".

up vote 1 down vote accepted

I have a degree in chemical engineering and we do heat transfer and vaporization.

Yes colder water that goes past the heating element and is not vaporized will have to be heated more.

There is a temperature sensor that will deliver more heat as required.

How it Works: Coffee Maker

Yes cold water will come out colder but colder by 10 degrees going in will be less than 10 degrees difference coming out.

Once it has been on the burner for a while that will determine the equilibrium temperature.

I had a drip machine that had a temp setting and it would indeed deliver hotter coffee.

A good reason to not use hot water from the tap is minerals. Hot water from the tap that was heated in a hot water tank will likely have more minerals due to the tank itself, and these minerals will contribute to scaling in the machine. Also hot water will have more mineral taste (but you probably would not taste it in coffee).

  • That video shows exactly what I was talking about, pushing non-vaporized water up the "geysir". If the coffeemaker would vaporize ALL the water and then condensate it back to liquid, it might take much longer to brew a cup of coffee. Also it would eliminate minerals and other impurities by basically distilling the water, but that would not be viable option to make drip coffee. – diynevala Jan 12 '16 at 10:36
  • Maybe I should have asked if there are such cheap coffeemakers that unintentionally make cold coffee. – diynevala Jan 12 '16 at 10:37

I hardly believe this is directly related to coffee. Still, as a more than 15 year experienced engineer, I would like to answer this question.

The answer is simply and clearly "no".

For the water to be able to travel to the top of the drip coffeemaker machine, it requires to gain some latent heat by changing its state to gas phase first. That's It simply means, it needs to be vaporized first.

Then, just at the top of the coffee and filter, there is a condensation space. At that space the gas (vapor) returns back to liquid phase (water) and starts to drip. Therefore, you obtain a slow flow of heated (to the near evaporation point) dripping water.

I cannot think any other way of bypassing this flow. Even in cheaper drip filter coffee makers.

  • I understand how the coffeemaker is supposed to work, but if the cool water fills the tube leading past the heating element, and only a portion of the water is vaporized, could some of the cool water simply gets pushed up by the pressure? If the rising tube is tight enough, the steamy bubbles can't get past the cool water, thus pushing it forward. I appreciate the answer, but will leave this open for a while, possibly will return with some measurements. – diynevala Jan 8 '16 at 6:09
  • @diynevala This may be possible. I have heard some scenarios in some piping installations where some liquid is mixed up with the gas phase. Bu those where oil rafineries where the gas was at quite high temperatures and could quickly and easily turn into liquid phase when the pressure drops even a bit. So, in extreme conditions, it might happen, but... What are the odds? – MT San Jan 8 '16 at 11:43
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    I am going to set up a test on this subject, otherwise it is going to disturb me a long time :D – diynevala Jan 8 '16 at 13:38
  • No the water is not all vaporized and condensed – paparazzo Jan 12 '16 at 14:10

It depends.

My office is currently in a temporary building that is powered by a generator. Once a week, they shut off our power to refuel the generator. Every week when the power is out, I make a pot of coffee in our commercial "drip" coffee maker and often get weird looks for making coffee with no electricity. This only works because the water overflows out of the tank with the heating element and drips over the coffee grounds. As long as the heating coils are still hot and I use the heated water out of our water dispenser, I get hot coffee out of the machine at 180 to 190 degrees F. Using cold water in this type of coffee maker always results in colder brewed coffee.

For the "geyser" type maker, not all the water reaches the point of saturated steam. It is possible for the water to be unevenly heated and the small steam bubbles push liquid up to the top of the coffee maker. The same effect can be achieved with air bubbles in an airlift pump. It is possible to get slightly lower temperature out of one of these makers using cold water.

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