Welcome back. In this post I will be digging into the second half of Fundamental 1 from my book, ‘HOW TO GET THE BEST FROM YOUR COFFEE’. This one relates to water temperature, as well as coffee density as a determination of what temperature to start brewing at. If you haven’t picked up the book yet, I do recommend giving it a read since this blog post is really meant to add to the ideas already presented in the book. You can purchase it here.
To begin with, I want to talk about how I came to the correlation of bean density and water temperature in the first place.
Over my many years making coffee I have encountered enormous variations in the nature of coffees from different origins, elevations, and especially roasting styles. I have always wanted to figure out if something consistent could point us as an industry toward brewing coffee with less guess work, and these variations are a huge inspiration to explore potential connection points.
More than a decade ago, I started to notice that coffees had better and worse flavour depending on how they were brewed. In particular, darker roasts had a big range of flavour. Visually dark beans would sometimes taste intensely bitter, or other times rather sweet with a bitter backbone. Don’t worry, this is not me revealing that I prefer darkly roasted coffee, but rather me acknowledging that (especially in the US) dark roasts used to be much more commonly preferred. The fact was that I was a barista and I wanted to make my customers happy with their drinks.
I was in an odd position at that point, and in my estimation I could have done one of two things: Accept that the coffee is darker than I like and not worry about it, or figure out how to get the best from a coffee despite the hurdles presented. Over time we figured out ways to make these coffees taste better. Up-dosing (basically using a smaller ratio, though we didn’t realise it at the time) was the common fix. Through experimentation we did find better results with many coffees, but I still hadn’t connected the dots personally.
Fast forward to two years ago.
When looking to connect these dots (hey, I get busy, time flies!) I tried numerous measurements to correlate with water temperature, but one thing stuck out more than anything else. I had begun testing whole bean coffee density to understand a better picture of a coffee, and I came across a washed Burundi from a US roaster that will remain unnamed. The coffee was incredibly dense (4.973g/cl!!) and no matter what I did I could not get it to taste good. It was always sour, extremely unpleasant, and never sweet. Grinding finer only created a stronger sour cup. In a moment of desperation to get anything positive out of the coffee I tried cranking the temperature to 211°F; basically boiling. After brewing it, the coffee was suddenly very sweet, balanced, and actually quite delicious. A coffee that didn’t seem like it had even seen 1st crack suddenly tasted amazing!
At this point a lot of trial and error and theorising took place to help prove my moment of clarity. The higher the density in the whole bean coffee, the more temperature it needed. And the opposite started showing itself to be true for a lower density. It is commonly understood that a lower temperature works well for darker roasted coffee, but now I had data in my hand that showed me why! It worked again, and again, and again, and again. Lower density coffees, even those that were roasted relatively light, necessitated less brewing temperature. Higher density coffees, even those that were deceptively dark in colour, tasted better with a higher temperature. The next step was to connect specific temperature with specific density. It is strangely convenient that the starting point of 200°F correlated quite well with 4.000g/cl density, and I almost didn’t want to believe it to be honest. But the results in the cup just could not be denied.
Now for the real discussion.
The theory behind the concept of bean density and brewing temperature is that your water temperature is directly connected to what types of compounds you want to extract from your coffee. We know from years of making cold brew that the result is low in acid and bitterness, but relatively high in sweetness, and plenty strong due to the long extraction time. If you have ever tried boiling your grinds you may also have connected high temperatures with more bitterness and acid. Taking those two examples as a reference, we know that low temp and high temp tend to bring out different things, and putting it into the range of 195-205°F, we can correlate that lower temp will be slightly less acid and bitter, and higher temp will be more.
The point of this is to match it with the nature of your coffee.
If your coffee is low in acid, it needs less temperature to extract the best flavours. If it is high in acid, it needs more. What I want you to understand is that the density is highly correlated to how much, or how little, acidity and bitterness tend to be in a given coffee. In very, very simplistic terms, high density equals high temp and low density to low temperature. The chart above is how to equate the precise temperature to use (for a pouring kettle)
You may have questions about this, and there are a lot of things to consider here. First and foremost I want to point out that this chart is a guide for a water kettle set temperature. That means that as the water loses heat as it drops, it is still capable brewing the right amount of compounds from your coffee. It also means that this chart is not exactly correct for batch brewing or espresso (I’m working on these charts!)
When you start to think about it, having something that works on a linear sliding scale is very uncommon in coffee. So I hope you can see the value in this correlation. There are of course outlying coffees which necessitate different temperature than their density conveys; decaffeinated beans, extremely underdeveloped but charred roasts, or unusually dense beans come to mind. However, since I believe this chart works quite well with most coffees, what is the next step?
The reality is that we should be measuring slurry temperature rather than water temperature, since that is where the whole energy transference occurs. This is of course highly difficult to do with most current brewing technology. I measured my slurry temps with a thermal probe held with clips for the book. Hint, hint, there will be a slurry temp post coming in the somewhat near future.
So with all of this, am I saying that the temperature measurements I present are the only good way to brew coffee? Most likely not. Remember that the other brewing fundamentals all interact with the coffee grinds as well. For example, a coarser ground particle size may necessitate a higher temperature to be capable of extracting enough from its interior cells. I have also found good (but different tasting) results with lower temperatures and very high agitation.
Knowing the principles of how each variable interacts in brewing will give you the power to adjust what you need to (or perhaps what you have control over) in order to get a better tasting brew.
Happy brewing, and don’t forget to read up! Next time I will be getting into brewer shape and material, one of my favourite topics.