# How do I boil water

### The simple solution

Wait until the water cools down by itself. Unfortunately, the waiting time can vary a lot depending on the container, lid, surface, etc. Or you can shake it back and forth between two vessels, because a lot of heat is lost in the process. Both are too imprecise, even for my taste. Besides, it says »Wait and see and Drink tea "and not" wait until To drink tea"

### Better: mix.

If you mix hot and cold water, it gets lukewarm. You didn't need any instructions for that now, would you? But we want to be a bit more precise and reach 70 ° C. Richmann's rule of mixing helps us here, which we greatly simplify for our purposes. If you don't feel like doing math, you can simply use the table at the end of this article.

Warning: Dear math and physics teachers, please do not read any further. It's getting terribly inaccurate now. Dear students, please do not copy here. If you use that in the next class test, you will fail.

The mixing temperature of two liquids of the same type results from the amount of the two liquids and their temperatures. If you mix one liter of boiling water with half a liter of cold water (room temperature), you get 1.5 liters of water with a temperature of a little over 70 ° C. It is calculated as follows:

in our example:

and thus 73.3 ° C, which is pretty much the required 70 ° C.

In the kitchen, however, you almost never have hot water at 100 ° C because it cools down a few degrees if you just take it off the stove. In practice, we calculate with 95 ° C and get according to the above formula exactly 70 ° C. For practical use, you should also remember that of course you need a 1.5 liter pot, otherwise there will be a flood.

### Does that help us now? Not necessarily.

Anyone who has thought about it will have noticed that we have so far answered the question of what mixing temperature results when we pour a certain amount of boiling and cold water together. But we actually want to know how much cold water we have to pour into the boiling water to get a certain temperature. So we have to rearrange the formula:

So if we want to get a liter of boiling (practically 95 ° C hot) water down to 60 ° C, we do the math:

and then we know that we need almost the same amount of cold water, namely 0.875 liters. Again, please think of the flood.

### Too complicated?

If you don't feel like memorizing the formula and always have a calculator lying around in the kitchen, you can use the following table as a guide. We always mix a liter of boiling water with the specified amount of cold water to get the target temperature:

 Target temperature Amount of cold water 90 ° C 0,07 No more than a shot of cold water ... 85 ° C 0,15 80 ° C 0,25 Or a large cup full ... 75 ° C 0,36 70 ° C 0,5 Two large cups ... 65 ° C 0,66 60 ° C 0,875 55 ° C 1,14 50 ° C 1,5 From here it gets pointless ...

### The commercial alternative

If you have a meat thermometer, you can save yourself the trouble. If you don't have one, you can buy one. However, you should make sure that it also shows temperatures and not just small pictures of cattle and pigs.