Water - The importance of water composition in Espresso

By any measure, coffee is the most complex beverage in the world. Comprised of 98-99% water, the entire science of coffee comes down to the absorption and extraction of solids and oils found within the beans. This rate of absorption, and the solids and oils which are extracted, are determined by a whole host of variables:

Source: Schrödinger’s water for perfect cup of Coffee, Chemistry World Blog 6/11/2014 (credits)

The least understood, but likely most important is the water. Yes. If you are spending $17 per 12 oz bag of coffee and not spending the time and effort to perfect your water, you may be missing out on many of the hidden flavors still locked in the beans. Water is a canvas for these flavors. The mineral composition and chemistry of the water is as much a determining factor to what you are tasting as the beans themselves. 

So, how do you perfect your water? There are as many opinions as there are roasters. The SCCA has released general guidance to improve the "overall" flavor of extracted coffee

However, recent research has uncovered that it isn't necessarily the overall total dissolved solids (TDS), but the actual minerals that are dissolved. Christopher Hendon (a PhD student at the University of Bath) and Maxwell Colonna-Dashwood (a World Barista Championship finalist) have studied the chemical composition of water and methods to deliver the best flavor.

“We’ve found that the water composition is key to the proportions of sugars, starches, bases and acids extracted from a particular roast.”

Hendon explained: “Hard water is generally considered to be bad for coffee, but we found it was the type of hardness that mattered – while high bicarbonate levels are bad, high magnesium ion levels increase the extraction of coffee into water and improve the taste.”

The study also found that sodium rich water, such as that produced by water softeners, didn’t help the taste of the coffee either.

Hendon added: “There is no one particular perfect composition of water that produces consistently flavoursome extractions from all roasted coffee. But magnesium-rich water is better at extracting coffee compounds and the resultant flavour depends on the balance between both the ions in the water and the quantity of bicarbonate present.”

Achieving this water nirvana is both extremely difficult, expensive and depends on the beans that you are using. However, cafe owners and roasters have started taking notice. There are now commercially available systems that will strip the water with reverse osmosis, and then re-add the ideal elements for better tasting coffee ("formulating water"). GC Water is one of a number of growing companies offering these systems to restaurants cafes. 

GC Water AB Formulator

Says Portola Coffee Lab's Jeff Duggan: 

"After extensive cupping's using formulated water compared to various other sources, the benefits of this system were crystal clear.  The role of water does not play second fiddle to sourcing and roasting coffee.  They all share equally important roles in creating that elusive "perfect cup."

Obviously, you would need to be a very, very aggressive home enthusiast in order to justify these systems, but you can see a future where there is a water filtration and dosing system for home enthusiasts. Until then, here are some steps you can follow to better your water:

1. Measure: Spend some money testing your water to see what you are starting with. This isn't just for hardness - measure the other minerals in your water as well. It is important to know that your municipal tap water quality will vary dramatically from month to month. A rainstorm has a tremendous impact of water minerality, for example.
2. Taste Test: Taste test as much water and coffee as possible. Can you tell a difference between certain types of water? This is easy to do with bottled water. For example, try Acqua Panna water (a high mineral favorite among Italian espresso machine manufacturers) with your favorite beans, and then test your water versus this to see where your municipal water is lacking. 
3. Filter: Review filtration company test results to see what filters get you to the magic TDS amounts. 

If you are nerdy home enthusiasts like us, you will find a long, fun process of determining water quality and what you prefer for a relatively small price. Keep in mind, that while researchers have shown that water softened with sodium might not be best for flavor - SOFT WATER IS ESSENTIAL FOR ESPRESSO MACHINES TO FUNCTION CORRECTLY.