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What is the best way to roast coffee for different waters?

We've all experienced it, we taste a delicious coffee, we buy the beans home, brew it and it doesn't taste the same. Is water the culprit? How should roasters respond to different waters used by their customers?

Imagine popping a spoonful of ground coffee beans into your mouth. That's your daily dose of coffee. Doesn't sound too pleasant does it? There's a key ingredient missing, water.

Coffee is 98% water while espresso is 94 - 95% water. It stands to reason then that water is an incredibly important ingredient in the whole coffee equation.

Why then is it so often overlooked in many situations? More importantly, is there a best practice for roasting to different waters?

How does water change the coffee experience in the cup?

If you've not already read Christopher Hendon and Maxwell Colonna-Dashwood's book, Water for Coffee, I highly recommend it as a strong starting resource into understanding the science behind water and its huge impact on the resulting coffee.

By now, we understand that pure H2O on its own, is not the best water for brewing coffee. It lacks minerals, which is the main party responsible for much of the extraction of coffee compounds into the water.

Soft water, with lower mineral content, can therefore be inefficient in the extraction of flavours and sugars into the coffee. On the other hand, it can also present a cleaner and lighter cup as there will be a correspondingly lower extraction of undesirable compounds extracted into the cup.

In contrast, hard water, with its higher mineral content is much more efficient in the extraction of coffee compounds. It results in coffees with more intense flavours and stronger bodies. However, the flipside of this is also a higher bitterness and astringency from over-extraction of the coffee.

As you will see in one of our discussion videos below, acidity is also one of the key aspects affected by the composition of the water.

What it means for the consumer

As a consumer then, it becomes a gamble when buying coffee beans. We never know what kind of water the roasted coffee was optimised for and how our brew water differs from it.

Personally, I believe it is better to purchase locally roasted coffee as it was probably optimised according to the shop's own filtered water. This would be closer to what we have at home, It will be easier to replicate their results even though there can still be differences in water within the same region.

With international roasters, there's no way to know what water they were roasting to and optimising for. Plus, you should be supporting your local roasters anyway!

How to roast for softer / harder water

In our own experiments, we found that softer water tends to heighten the acidity of the coffee and almost made it sour. To compensate for this, we had to roast a slower, more developed coffee to achieve the overall balance that we were looking for. 

In contrast, harder waters tend to provide higher sweetness and body but dulls the acidity almost to the point of being flat. As a result, we compensated with a faster and shorter roast especially towards the end if we wanted to achieve a more vibrant cup.

This  is contradictory to the findings from this blog post from Chromatic Coffee.  According to them "what we've found is that the shorter the roast, the lighter the water we want to use, and the longer the roast, the heavier the water. In light roasts, the lighter water seems to be able to better pull sweetness from the bean".

There hasn't been any conclusive evidence on specifically roasting differently for different water compositions. I guess it's high time that we run some experiments on this. If you have any experiences in this regard, please do leave a comment below and let us know what you've found.

So how should roasters respond?

As a roaster, how should you roast for the different waters out there? Should you

a) roast specifically for your own shop water
b) roast specifically for softer water
c) roast specifically for harder water
d) roast and try to optimize for a lower but acceptable standard across a different range of water hardness 

Let us know your response and what you think should be the best practice in the comments section below.

Want to become a better coffee roaster? Check out our Ultimate Coffee Roasting Course! You'll get access to all our secrets, knowledge and experience in coffee roasting plus masterclasses from roasting champions around the world!

And if you have any coffee questions you'd like us to answer, leave them in the comments section below and we'll make sure to answer them in future posts.

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