Before we answer the question, "does coffee taste better with alkaline water," we first need to answer the question, "what is alkaline water?"
In scientific parlance, the term "alkaline" refers to a pH level above the neutral 7.0, on a pH scale from 0 to 14.
All solutions with a pH above 7.0 are called "alkaline" and all solutions below 7.0 are called "acidic."
In the scientific community, "alkaline water" would be any water that tests above 7.0 on the pH scale, such as an alkaline lake.
In vernacular parlance, especially among health conscious consumers and gourmet cooks, the term "alkaline water" has come to mean water used for drinking and cooking that has a pH higher than tap water, i.e. it's less acidic than tap water.
The term "slightly alkaline" is often used for this type of "alkaline water" because the pH is only a little above 7.0, usually in the range of 7.1 - 7.5.
Alkaline water, as used in the vernacular, is alkaline because it contains alkalizing agents. These include minerals like calcium, magnesium, potassium, and silica.
Alkalizing agents also include bicarbonate, also known as hydrogen carbonate. Chemically, bicarbonate is considered a salt. It is very good at reducing the acidity of the foods and fluids you ingest and also at buffering the lactic acid in the stomach.
Does Coffee Taste Better with Alkaline Water?
The short answer is yes! Lets look at why coffee taste better with alkaline water.
The flavor in coffee is concentrated in the essential oils of the beans. This is true for most plants in fact.
To brew a great pot of coffee, you'll need to extract out as many of these flavors as possible, without destroying them afterwards of course by raising the temperature too high!
When you brew coffee, it's the combination of the minerals in the water and the hot temperature that extracts the flavors from the oil in the beans.
Plain water can't do this! If you use water that lacks minerals, or is too low in minerals, you'll get flat flavorless coffee.
If want to brew a great cup of coffee, you'll need to start with alkaline water with rich mineral content to tease those flavors out of the bean oils.
Coffee chemists use a term, "total dissolved solvents" (TDS) to denote the flavor particles that are extracted from the beans. High TDS usually means a good cup of coffee.
Astringency is another factor in how coffee feels in your mouth and it's directly proportional to how many tannins end up in your coffee. Higher astringency (more tannins) gives you more of a "sharper" or "puckery" feel and taste.
This is because tannins cause mucus membranes to shrink. Generally speaking, you'll get more tannins extracted the alkaline the water.
Thus, if you are using coffee beans high in tannins and you use water that is more alkaline, you may end up with a sharper flavor than you want, although some people prefer this.
A Word of Caution About Going too Alkaline
If you use water with too many minerals, i.e. it is too alkaline, you will get more scaling (liming) on your coffee pot.
While this won't affect the performance of a drip pot unless it gets really bad, even a small amount of scaling can affect the performance of an espresso coffee maker.
A Word About Tap Water Variation
If you use tap water to make coffee over several days, no matter how precisely you measure out the beans and the water, you'll likely notice a wide variation in the taste and quality of your coffee.
This is because municipalities add chemicals to treat their water at different times. Some days you'll have more minerals and bicarbonate in the water than other days and this will greatly affect the taste your coffee.
Final Thoughts
The pH and mineral content of coffee can dramatically affect the flavor of coffee. This is why alkaline water with a nice complement of minerals brews better coffee than acidic water which generally lacks minerals.
