Brewing coffee in any form is a basic dissolution reaction where the soluble particles or solute (coffee) dissolves into the solvent (water). At what rate and to what degree this occurs depends on the following: The solubility of the coffee in water, the chemistry of the water, the temperature of the water and the duration the coffee is in contact with the water.
More important than the coffee itself is the water. Without water there would be no life on earth, no life on Mars, no ice, no steam, no clouds, no lakes, no ocean and alas no coffee-grown or brewed. To bring to life the most from your coffee it is critical to understand the role water plays when brewing coffee from both a flavor stand point and a consistency standpoint. We must consider the exact chemistry of the water we are using to brew our coffee, which plays a significant role in brewing the perfect cup and finding the 100 point coffee! So let's explore each attribute of water as it relates to brewing the ultimate coffee.
Chemistry of Water and Coffee
Coffee is so much more than a simple beverage—it's a complex chemical experience influenced primarily by two key elements:water andcoffee solubles. Understanding their relationship gives us critical insight into the flavors and aromas we enjoy in a cup, and how to get the most out of each coffee we purchase.
Water: The Universal Solvent
Water makes up about98–99% of brewed coffee. Its unique molecular structure (H₂O) allows it to be an excellent solvent and is often referred to as the "Universal Solvent", meaning it can dissolve a wide range of compounds. However, not all water is created equal in the context of brewing coffee. Themineral content or TDS—especially calcium, magnesium, and bicarbonates—affects how well it extracts and binds to the flavor compounds in coffee:
Hard water (high in calcium and magnesium) can over-extract certain compounds, often leading to bitter flavors.
Soft or distilled water lacks minerals and can under-extract, resulting in flat, sour coffee.
The ideal water for coffee contains a balanced mineral (TDS) profile with moderate hardness and a neutral to slightly acidic pH (~6.5–7). The best way to get the perfect TDS in water is by treating distilled water with coffee extraction specific minerals. Using something like Third Wave Water packets or similar.
A note - without all the chemistry and focus on TDS (total dissolved solids) etc, ultimately cold tap water can be used as long as it tastes and smells good as drinking water it will likely produce a good tasting coffee. Our senses after all can be used to inform us of many qualitative and quantitative things in the context coffee so don't get too lost in the weeds trying to make your water absolutely perfect. Try to avoid filling your water kettle with hot water from the tap. Super Hard water and highly chlorinated water or water which has other metallic or chemical flavors often will translate through into the final cup.
Coffee: An Immensely Complex Chemical Mixture
Roasted coffee contain over 1,600 compounds--significantly more complex than wine--that comprise the aroma and flavor. When ground and exposed to hot water, several groups of molecules which we refer to as the coffee solids dissolve into the solution:
Acids (like chlorogenic, citric, nicotinic, quinic acid) contribute brightness and complexity of the final extraction.
Caffeine is a bitter alkaloid that is a stimulant. Caffeine works by blocking adenosine receptors in the brain, preventing adenosine from binding and inhibiting neural activity. At appropriate concentrations this leads to an increase in alertness, focus, and reduction in fatigue. It's overall effect on the taste in coffee is minimal.
Sugars and carbohydrates influence body and sweetness.
Lipids and oils (especially in espresso) provide mouthfeel and richness. Different species and cultivars of coffee have different levels of lipids making coffee selection important for texture in espresso.
Maillard reaction products, Ultimately "Sugar browning" including melanoidins, give roasted coffee its deep color and toasted, caramel-like flavors.
Extraction and Balance
The brewing process aims to extract the perfect amount of desirable compounds from the above list while minimizing harsh or undesirable ones. This is a dynamic system influenced by:
Grind size -Size does matter, and so does size distribution--what is the ratio of particle size variation in your grind?--Finer particles have a greater surface area, thus result in a higher degree of solubility in water. Conversely, coarse particles have less surface area and result in lower solubility. The modality or ratio of small particles to large particles produced by your grinder is important for even extraction. We recommend (Baratza Home Grinders). Matching grind size to brew method and water temperature is crucial for an even and uniform extraction.
Water temperature - (ideal is 200F-204F) Ensuring the proper brew temperature is critical from the standpoint of avoiding over extraction of chemical compounds found naturally in coffee. These primarily consist of; chlorogenic acid (the ester formed between caffeic acid and L-quinic acid for those keeping track), Nicotinic acid (AKA Niacin), trigonelline, cafeol and to a lesser degree caffeine. Over extraction simply leads to an increase in perceived bitterness or acidity and makes for a more tangy often metallic tasting cup.
Brew time -Dependent on the extraction method. But as time tends to drive dissolution reactions, the longer the coffee particles are hanging out with the water the more the coffee solids will extract into your solution. So this needs to be modulated to fit the brew method with grind size and water temperature.
Water-to-coffee ratio -Again dependent on extraction method.
Post Roast Degassing -Degassing kinetics play a significant roll in extraction dynamics and yield. Also, significantly influence flavor and mouthfeel. We encourage waiting 7-10 days post roast to fully enjoy espressos, and 3-5 days post roast for filter / drip. However - see my article on this very topic to learn more here.
Too little extraction results in sour, underdeveloped flavors. Over-extraction can bring out bitter, dry tastes.
As a side note, from the perspective of caffeine extraction--if the buzz is what compels you to drink coffee--caffeine chemically is most soluble in liquid water at 212 degrees F at a whopping 67.0 g/100 mL and even more so in water vapor as steam. So if you are just looking for a wicked buzz--or to just feel super edgy & anxious--dark roasted coffee, finely ground hit with superheated steam condensed in a beaker and voila, next stop the moon.
A few takeaways; while brewing the perfect coffee does require an source of high quality water, great coffee can be brewed with a variety of water types, from a variety of sources. However, can we brew a 100 point coffee with just any water?
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