Crafting Coffee Water
I’ve tasted countless coffees across the US and abroad at cafes using freshly roasted beans from reputable roasters. I’ve developed an expectation of great taste when I see familiar names like Madcap, Parlor, or Tim Wendelboe on the menu, to name a few. The vast majority of these visits are met with great tasting, well-balanced coffee. These cafes have brewed each batch with attention and have kept their parameters dialed-in. On some visits however, the coffees I know to have clear and punchy flavors turn out to be heavy, chalky, and stale in taste. The culprit of these unwanted flavors almost always lies with the quality and minerality of the cafe’s water.
Despite the cafe brewing high quality coffee and checking their parameters (grind size, ratio, agitation...), the final product can land off-target “just” because of their water. Coffee lovers brewing at home may run into a similar issue without the right water source. As my appreciation for coffee grew, I found myself asking more and more questions about water composition and how it affected my brewing. I would get so excited after purchasing a new, awesome sounding coffee only to come home and brew through the whole bag in a day dialing it in and wondering why it didn’t come anywhere near what was expected. Now, for some geographies with generally soft water, this may not be as big of an issue. However, if you find yourself searching for those great flavors and being let down, water may be your answer. Let’s get into why water is so important and how cafe owners and home brewers alike can solve their water woes.
I was never a chemistry whiz in school, but thankfully water chemistry isn’t that complicated once you understand a few guiding principles. Trust me, read to the end. It’s easy.
How Water is Measured
Water has two measures of hardness: General Hardness (GH) and Carbonic Hardness (KH). Both GH and KH are measured in terms of milligrams per liter (mg/L) or parts per million (ppm). mg/L and ppm are numerically similar, so 100 mg/L = 100 ppm.
GH is a measure of the water’s calcium and magnesium levels. This number will be different from what a TDS meter will measure because GH standardizes the concentration between magnesium and calcium in terms of CaCO3. The chemistry and math behind this can be tough to fully understand, but don’t worry we will offer straightforward measurements soon.
KH is a measure of the water’s bicarbonate level. This is also referred to as alkalinity. Bicarbonate levels are not measurable with a TDS meter, and often times can go overlooked.
The most accurate and accessible way to measure both GH and KH is to use a titration drop kit. There are many on the market, but this one linked here offers the greatest resolution for the price. Also, here is a great in-depth video on how to use the kit. These drop kits will measure the hardness levels in terms of “degrees”, but these degrees can be easily converted to mg/L by multiplying degrees by 17.85. For example, 3.2 degrees = 3.2 x 17.85 = 57.12 mg/L. Otherwise, the test will specify the correct conversion.
The Importance of GH and KH
GH determines how good of a chance your water has at extracting the sorts of flavors most desirable in coffee. When you brew coffee, the water doesn’t just dissolve the components of the coffee at random. Think about how magnets work. Magnets are only attracted to certain metals. Calcium and magnesium in your water are like magnets. While perfectly pure water (without minerals) can dissolve some parts of coffee, calcium and magnesium bind to and extract the specific and desirable parts of the coffee we are after. The compounds in coffee that contribute to sweet, acidic, and floral tastes and develop a coffee’s body are attracted to calcium and magnesium. Calcium and magnesium together create GH, and this is what gives your water the ability to extract great flavors.
KH has an unusual ability. KH measures the level of one mineral, bicarbonate. Bicarbonate, also known as buffer, has the job of maintaining the water’s pH level. If the water solution starts to become too acidic, bicarbonate has the ability to transform acids it comes in contact with into bases. Because coffee is a weak acid, bicarbonate can actually work against the acids that give coffee its flavor. A high KH level relative to the GH level will inevitably lead to heavy, chalky, and stale tasting coffee every time. However, some KH is good because it helps to balance out a coffee’s acidity and promotes a more balanced cup. The trick is getting both GH and KH to proper levels and keeping them in check.
Recommended Hardness Levels
Because taste is subjective, the ideal level of GH and KH are debatable, but below is a recommended range. This range should provide a good balance of minerals while maintaining a manageable level of hard water build up.
GH: 50 mg/L - 110 mg/L
For optimal flavor and very low hard water issues try to shoot for an even split between calcium and magnesium and don’t be afraid of a strong bias towards magnesium. Some coffee professionals opt for an all-magnesium makeup for GH.
KH: 35 mg/L – 70 mg/L
A good rule of thumb is to maintain the KH level at half the GH level. This will promote the most balance of acidity in your coffee.
How to Apply All This Knowledge
Some cafe owners may have available resources and opt to purchase a new water filtration system that will create hundreds of gallons of water within these specified ranges. If interested, you can simply contact a local water filtration company or Tinker Coffee for more assistance. There are a couple options that range from fully automatic filtration systems that keep your water in range (all you need to do is periodically change filter cartridges) to reverse osmosis (RO) systems that will strip all the minerals out of the water. These RO systems will fill up holding tanks that provide you with a blank slate to add the minerals back in manually and give you more control.
For home brewers that are interested in taking their water skills to the next level, here’s a hack I use to produce perfect water at home. I have a 5 gallon jug that I fill up with filtered reverse osmosis water at my grocery store pretty cheaply (around 39 cents per gallon). With a little bit of math, I can add minerals back to my “empty” water and achieve my desired minerality levels. You can do this with 1 gallon jugs too, or you can buy 1 gallon jugs of distilled water. Distilled water will be ultra-pure, with a TDS close to 0 whereas reverse osmosis may carry a TDS of 5-10 mg/L, but either will work just fine.
The Math and Needed Supplies
The Scale - I like to use a super cool and cheap gram scale that measures to the hundredth of a gram. Here is the Amazon link. With this, you can accurately mix water in as little as one liter batches. If you have a cafe and are adding minerals to a large water reservoir (20-100 gallons), you typical tenth of a gram scale will work just fine.
Bicarbonate – It’s just baking soda!
0.64g : 1 Gallon = 100 KH per Liter
Magnesium – It’s just Epsom Salt!
0.94g : 1 Gallon = 100 GH per Liter
Calcium – It’s just calcium chlorides… like what’s used in canning. Trust me you can find it at the grocery!
0.55g : 1 Gallon = 100 GH per Liter
My recipe: Great coffee water in 4 easy steps
Super Cool Diagram for Easy Summary