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How hot should your water be when you make coffee?

September 23, 2017

If you like Breaking Bad then you’ll enjoy this video. If you like my website then you’re probably sick of me posting it! (No spoilers, I wouldn’t do that to you.)

I think that’s the 3rd or 4th time I’ve embedded it somewhere on here. But I’ve done it with good reason as it illustrates an important point in an entertaining and humorous way.

Extracting coffee from the coffee bean is a chemical reaction. Make the ingredients react under certain conditions and you get coffee. Make the ingredients react under very certain conditions and you get great coffee.

All these things do is manipulate the chemical process. The two main variables in the brewing process are strength of the coffee and extraction of the coffee. Everything you do affects either the strength or the extraction and dictates whether your cup of coffee will sing and dance like the balanced set of flavors it is.

It is of course true that the ingredients themselves are critically important. A good water source and high quality coffee beans that are freshly roasted and have been recently ground are the foundations. To build upon that you need to make sure certain other elements of the brewing process are on point.

Today I wanna look at one of those elements. Temperature.

How how should your water be to make great coffee?


Strength vs Extraction

I mentioned that the two main variables when brewing coffee were strength and extraction. When it comes to discussing temperature, it only affects the extraction, but I’d like to discuss strength for completeness sake.

The strength of your coffee is a product of how much coffee you use to how much water you use. It’s commonly referred to in a coffee:water ratio such as 1:14, 1:16 or 1:8. So for example a 1:14 coffee water ratio would include 20g of coffee and 280g of water. Somewhere around the 1:15 mark is good starting point and you can adjust based on your tastes.

If you’re interested in a big caffeine buzz then the only thing to play with is the amount of coffee. Most people would agree that 25g makes you a pretty strong cup, with 17-20g being the range for a regular cup. And don’t worry about brewing longer, caffeine is extracted early in the process so lengthening your brew will not squeeze out any more.

Coffee strength is easy to change and play with providing you have a reliable way of measuring your ingredients. It’s for this reason that I highly recommend getting a cheap 0.1g scale for anyone who doesn’t consider themselves a beginner.

How does increasing temperature change your coffee

The soluble flavors and micro-particulates in coffee are extracted, to some degree, at any temperature. Anyone who’s made a batch of delicious cold brew coffee by putting cold water and ground coffee in their fridge can testify to that. It does take a day or two, of course!

The opposite is not true. You may remember from 4th-grade science class that if you make water too hot, it turns into steam. So if you make your water hotter than its boiling point at 212°F (100°C), you’re not going to even have water any more.

(I guess it’s theoretically possible you could extract coffee with steam? I’ve never seen or heard or anyone attempt this madness, though.)

Providing your H2O is in its water state, higher temperatures cause your coffee to extract faster. When you add water that’s near boiling – say 205°F (96°C) – to ground coffee then you know those compounds, sugars and flavors will be dissolved into the water much faster than if you were to add water at 180°F (82°C).

The science behind over and under extractions

The big issue of making your coffee is getting the right extraction. An overextraction can be caused by many factors but the end result is bitterness. When the coffee yield reaches over 22% the later-extracting bitter compounds and balancing sugars are over-absorbed into the coffee and ruin the taste by making it bitter.

An underextraction is similar, again it can be caused by many factors by the end result is sourness. When the coffee yield is under 18% the early-extracting acids dominate the dissolved solids and cause a biting acidity.

Here’s a graphic plotting extraction (along the bottom) against strength (along the side) which might help a little.

Sidenote: This is the reason why an even grind consistency is SO important to good coffee. If you have lots of fines in your grounds they each will massively overextract and collectively ruin your brew.

The yield is affected by four things:

– Water Temperature
– Brew Time
– Grind Size
– Brew Method (to a lesser extent)

That’s not to say that nothing else affects the taste of your coffee (*cough* freshly roast and grind your beans *cough*) but that these affect the yield and so affect the chance of over or underextraction

What the answer actually is

So what is the answer, I hear you ask, how hot should your coffee be? Well, there is no answer. For every brew method, grind size and brew time there cannot be one temperature that works for all of them.

You remember that Breaking Bad video above where Gail states he keeps the temperature no higher than 92°C? Well that’s great as long as it is kept in line with the other variables.

As a general rule, if your coffee tastes sour then increase the brew time, temperature or decrease your grind size. If your coffee tastes bitter then decrease your brew time, temperature or increase your grind size. If you need a starting point then look for a brew guide from a reputable website and adjust from there. And remember, no amount of tinkering is going to cover up your 6-month-old cheapo coffee beans.

This can actually be very helpful. If you like your coffee scalding hot, then use the water straight from boiling and use a shorted brew time or larger grind size. If you hate having to wait for your coffee to cool down to an acceptable temperature (i.e. me), use a cooler temperature while upping the brew time or using a smaller grind size.

cup of coffee with sweets

Balance your temperature with brew time and grind size and you might have something that looks like this.

What this hopefully has shown you is how important knowing the temperature of your brew can be. A lot of people will spend thousands on a top-tier grinder, spend ages researching the latest brew method and time their brew time down to point-one of a second while ignoring the temperature. If this is you, think about getting a thermometer kettle.

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