Can I boil water to temperature lower than 100 Celsius / 212 Fahrenheit to make a tea?

Question

For many years I had a typical electric kettle. Whenever I wanted a 75 Celsius / 167 Fahrenheit water to make a green tea, I had to boil it up to 100 Celsius / 212 Fahrenheit (because, that was the temperature, where each my kettle was stopping to heat) and wait.

Now, I've got an electric kettle with a thermometer. Can I boil the water only to 75 Celsius and stop? What is the typical temperature, in which all (most of) germs in water are killed and water becomes drinkable?

I've heard, that this is 70 Celsius / 158 Fahrenheit, so my idea would have a ground. Am I right?

Answer 1

Technically, your idea seems sound. But I wouldn't do it.

What you are proposing to do in your electric kettle is very close to the standards for flash pasteurization. According to wikipedia, the standard procedure for flash pasteurization is to heat and circulate the liquid at 71.5 °C (160 °F) to 74 °C (165 °F), for about 15 to 30 seconds, which results in a five log (99.999%) or greater reduction in bacteria. Other journal articles seem to indicate that some protozoa like cryptosporidium are killed by flash pasteurization, but others, like giardia, might survive in small numbers.

I suspect the guideline for boiling water in issues of safety and in recipes is used because steam and bubbles are such convenient guarantors of temperature.

Psychologically, though, this makes me a little nervous. Personally, I would boil the water- if you have time for tea, you have time to boil water. It is possible, though, that you are a more adventurous tea drinker than I am.

Answer 2

You cannot boil water at 70 Celsius. Maybe this is a language problem; "boiling" means taking water to the state where there are lively bubbles popping on the surface all the time, and it is steaming profusely. It boils at 100 Celsius at sea level and a little bit below it when you get higher, but the difference isn't that much. Even in the highest towns in the world, at more than 5000 meters, water boils at just below 90 Celsius.

When you get your water to 75 Celsius, you are heating it, not boiling it. Heating water certainly kills bacteria - in fact it is the heat which desinfects water, not the boiling - but we cannot tell you which bacteria are killed and which are not. US/Western Europe guidelines for food safety suggest temperatures up to 70 Celsius for safe food preparation, but these suggestions are based on many things, such as the type of bacteria found in these parts of the world, statistics showing how many people get sick from underheated food, and so on. It is entirely possible that your water is contaminated with something different than whatever is present on US meat.

If you do not have access to tap water, or the water supply in your city is not considered safe, and there is a directive to boil water, then this is what you need to do to be officially safe. And it means real boiling, at 100 Celsius. Nobody is equipped to tell you whether 70 Celsius is sufficient for your case or not.

Update As the commenters suggested (and Wayfaring stranger linked an official source for it): The safety guidelines are not just to bring the water to boiling, but to hold it at a boil for one minute.

This means that the flash-kill temperature for the bacteria must be well over 100 Celsius. A small explanation about food safety: There is no temperature at which all individual cells in a bacterial colony keel over and die. Bacterial death is a function of temperature and time, and some hardy individual cells can withstand a lethal temperature for some seconds. This is why you either have to incinerate them outright with a really high temperature - which seems to not be possible to reach with boiling the water - or wait a bit on a somewhat lower temperature until every bacteria is dead, in this case 1 minute at 100 Celsius at low altitudes, or, because you cannot reach 100 Celsius when you are up in the mountain, 3 minutes boiling at high altitudes.