Recently my old faithful kettle bit the dust, and I had to invest in a shiny new one. While it wasn't a great hardship to do so, it did mean that I could no longer rely on experience to "just know" when my water was at the perfect temp for my coffee brewing. With my old kettle, I knew to grab it just before the whistle started, and the water would be at that sweet spot of 195º (give or take a degree or two). My new kettle and I haven't worked out a similar system yet, so out came the old cooking thermometer. And then out went the old thermometer because it no longer worked. (Isn't it ridiculously frustrating how large these little problems seem before you've had your daily java fix?)
Thankfully, one of our founders had the random knowledge of how to tell when your water was at the perfect temperature based on the water bubbles during the boil. (You can check out where he got his traditional Chinese tea brewing knowledge here and here.) Inspired by that and those times when you just don't have a cooking thermometer or a kettle with a long-term relationship history handy, we decided to do a post of our own on hacking your perfect temp.
There are several schools of thought over the perfect temperature for your coffee. Googling Perfect Coffee Temp resulted in 1,180,000+ results. Virtually everyone agrees that unless you are some sort of 1800s cowboy, you shouldn't use 212ºF or 100ºC water - aka full on boiling - because you will burn your coffee and then it will taste bitter. (If you are an old timey cowboy reading this, welcome to the future! Now fix your coffee brewing skills.)
The Chinese called this 212ºF rolling boil a "raging torrent." Thanks to the cowboy reference I just made, I'm rather fond of westernizing it with "rampaging stampede." Much like boiling water while you're brewing, it's something that you want to avoid.
Our ideal temp for day-to-day brewing (like for our 1 minute Americano) is 195ºF possibly going up to 205ºF but definitely not over. (So not actually boiling.) Less than 195º and there's a good chance that your grinds will be under extracted, possibly resulting in weak-flavored coffee. More than 205º and you run the risk of the burned, possibly bitter, coffee that our aforementioned cowboy drank.
The Chinese call the bubbles of this temperature sweet range a "string of pearls."
Is that the only temperature you should use?
Nope! Not by a long shot! Water temperature is only part of the brewing process. You'll also need to consider your grind size and brew time. A finer grind means that the water is exposed to more coffee, so you might need to fiddle around with different temperatures or times. You should also consider your brewing method or apparatus. If you are pouring over a cone, then you might want to consider a higher temperature given that the water is exposed to more air and might cool faster than in the AeroPress tube. In fact, Aerobie, the makers of the AeroPress, recommends using an even lower temperature, usually 175ºF or 185ºF for lighter roasts. Which brings up another good point: flavor profiles vary and all of the above mentioned things - grind size, water temp, brew time - can affect them. Sometimes you do just have to experiment, and then it helps to have a thermometer handy to you can recreate your perfect magic potion later.
One last thing...What should you do if you haven't had a chance to grab your water before it comes to a full boil? Honestly the easiest thing to do is just remove the water from the heat source and give it a about a minute or so to cool down. If you need to do something while you're waiting, pour that too hot water to into your mug to warm it up before brewing. Just don't be so anxious for your morning java that you inadvertently take a sip. And make sure you pour that water out before you press in your coffee.