Alkalinity in Coffee: What It Does to Taste and How to Dial It In
Alkalinity is the part of your brewing water that neutralizes acid. In coffee, that means it quietly decides how bright, sharp or flat your cup tastes. Too little and a good coffee turns sour and thin. Too much and it goes chalky and dull. For most filter brewing, a modest range of roughly 20 to 50 ppm as CaCO3 is a sensible place to start, and the rest of this guide shows you why, how to check your own water, and how to adjust it.
TL;DR
- Alkalinity is your water’s buffering capacity: its ability to resist a drop in pH when acid is added. Coffee is full of acids, so alkalinity decides how much of that acidity you actually perceive.
- Higher alkalinity makes coffee taste less acidic, lower alkalinity makes it taste more acidic. Alkalinity predicts this better than pH does.
- For most filter coffees, 20 to 50 ppm alkalinity as CaCO3 is a reasonable range. Espresso tolerates more, because the drink is so concentrated.
- “Alkaline water” sold by pH is not the same thing as water with the right alkalinity. Check the actual buffer, not the pH on the label.
- Adjusting at home is possible with baking soda, but the dose is tiny and errors add up fast.
Table of Contents
- What alkalinity means in coffee water
- Alkalinity vs. pH vs. hardness
- What high and low alkalinity taste like
- What alkalinity should you aim for?
- Is it okay to brew coffee with alkaline water?
- How to check your own water
- Adjusting alkalinity at home
- A worked example
- Our perspective: brew the coffee you were sent
- Put it to work with fresh ultra-light coffee
- FAQ
- Sources
What alkalinity means in coffee water
Alkalinity measures how much acid water can absorb before its pH moves. The Wisconsin Department of Natural Resources lab guide describes it as a measure that includes bicarbonate, carbonate, hydroxide and hydrogen-ion contributions, and notes it is commonly reported as mg/L or ppm CaCO3. In drinking water, bicarbonate is usually the part that matters.
Think of it as a sponge for acid. Coffee extracts a range of organic acids as water passes through the grounds. Water with a lot of alkalinity soaks up a large share of them, and the cup tastes rounder and quieter. Water with little alkalinity soaks up almost none, and every bright note arrives at full volume.
The Specialty Coffee Association describes alkalinity as buffering the acids extracted from coffee, which is why higher alkalinity tends to reduce perceived acidity. Coffee professional Scott Rao puts it simply: higher alkalinity generally makes coffee taste less acidic, lower alkalinity makes it taste more acidic, and that holds whether the water’s pH sits above or below 7.
That last point surprises people, so it is worth slowing down on.
Alkalinity vs. pH vs. hardness
Three numbers on a water report get mixed up constantly. They are related but not interchangeable.
| Measure | What it describes | Why coffee drinkers care |
|---|---|---|
| pH | How acidic or basic the water is right now | A snapshot. Tells you little about what happens once coffee acids arrive |
| Alkalinity | How much acid the water can neutralize | Predicts how sour, bright or flat the cup will taste |
| Hardness | Mainly dissolved calcium and magnesium | Affects extraction and scale, and is a separate property |
The Wisconsin DNR guide explains that pH, alkalinity and hardness can move together in natural water, but one cannot stand in for another. A water can have a pH of 8 and almost no buffer, or a pH near 7 and a heavy one.
The SCA says that when pH is near neutral (6 to 8) and alkalinity is above 20 ppm as CaCO3, alkalinity has a greater impact than pH on the acidity of the beverage. Its practical advice for designing coffee water is to prioritize alkalinity over pH, because alkalinity better predicts how extracted acids will be buffered.
Hardness deserves its own note. A 2026 sensory study published in a peer-reviewed journal found that, under its test conditions, bicarbonate had a pronounced effect on flavor, while calcium variation at realistic drinking-water levels produced little marked change. That does not mean hardness is irrelevant in your kettle or machine, only that for taste, alkalinity is the first lever to look at.
What high and low alkalinity taste like
Too much: flat, chalky, muted
In sensory testing reported by Daily Coffee News, high-alkalinity water produced flat, chalky coffee with muted acidity and muddled flavors. The same article reports that higher bicarbonate can generate extra carbon dioxide, which can enlarge bloom or espresso crema and get in the way of extraction.
The peer-reviewed study mentioned above is more specific. Raising bicarbonate, up to an experimental 300 mg/L, substantially reduced perceived acidity, fruitiness and complexity while increasing roasted and bitter notes in the Colombian coffee tested. The authors’ result came from one coffee under defined conditions, so treat it as a strong signal rather than a universal law. Still, it matches what many brewers notice: a lively washed Ethiopian can lose its citrus in the wrong water.
If you are curious about the bloom side of this, our own guide on how long to bloom coffee explains what the CO2 is doing in the first thirty seconds. Those who drink several cups a day might also wonder about brushing before or after coffee, since acidity matters for more than flavor.
Too little: sharp, sour, thin
With almost no alkalinity, nothing softens the acids. The Daily Coffee News piece, reporting on SCA guidance, places alkalinity below 40 ppm as CaCO3 as at risk of providing too little buffering. Note that this guidance reads differently from the narrower 20 to 50 ppm that some practitioners prefer, which is a reminder that these are ranges for taste, not laws of physics.
Very soft water is common in parts of the US. A BWT-published report on water for coffee uses San Francisco tap water as an example of very soft water, with total hardness and alkalinity below 40 ppm CaCO3. If you live somewhere like that and your light-roast coffee tastes sour no matter how you grind, the water may be part of the story. Our piece on dialing coffee acidity at home covers the other variables to rule out first.
What alkalinity should you aim for?
There is no single correct number. Published guidance clusters around a few ranges:
| Source | Suggested alkalinity (as CaCO3) | Notes |
|---|---|---|
| Scott Rao, general | 20 to 50 ppm | Reasonable for most coffees, depending on the coffee and your taste |
| Scott Rao, light roasts | 30 to 40 ppm | A personal target for lightly roasted, well-developed coffee |
| SCA guidance as reported by Daily Coffee News | Below 40 ppm risks too little buffer; an upper range around 75 ppm with harder water | The same article reports another recommendation of about 130 ppm for harder waters |
For ultra-light, Nordic-style roasts like the ones we ship, we lean toward the lower and middle part of this range. These coffees are built on high, clean acidity, and you want a buffer that keeps them from tasting sharp without erasing the florals and fruit you are paying for.
Why espresso is different
Espresso can handle higher alkalinity. The reason is dilution. The SCA compares a ristretto at a beverage ratio of about 1.5 with filter coffee at about 15, a roughly tenfold span. In a filter brew, a lot of water carries a small amount of acid, so the water’s buffer has a big effect. In a concentrated shot, much less water is available to neutralize the same acids, so the water’s alkalinity can be much higher before it significantly changes the acidity in the cup.
If you pull shots and want sweetness without losing clarity, see our blooming espresso recipes and the explainer on why crema forms, since bicarbonate and CO2 touch both.
Is it okay to brew coffee with alkaline water?
It depends on what the bottle actually contains. “Alkaline” on a label usually refers to pH, often 8 or 9. We have not found a reliable, independent measurement showing that this pH tells you anything about the buffer that matters to coffee. As the SCA’s reasoning above shows, pH is a snapshot and alkalinity is the capacity. A water can read high on a pH strip and still carry little bicarbonate, or the reverse.
So the honest answer is: sometimes, but you cannot know from the pH. Look for the bicarbonate or total alkalinity figure on the producer’s water report, convert it to ppm as CaCO3 if needed, and compare it with the ranges above. If a bottled water is advertised as alkaline and its report shows alkalinity well above 50 ppm, expect a rounder, quieter cup from a light roast. If the report does not list alkalinity at all, skip it for filter brewing, or taste it side by side with your regular water.
Some products are also marketed as “non-acidic” coffee made by treating the coffee itself. That is a different matter from brewing water, and it is aimed at people who avoid acidity, not at people chasing it.
How to check your own water
- Read your local water report. US utilities publish annual consumer confidence reports, and many list alkalinity or bicarbonate. Hardness and alkalinity are different lines, so make sure you read the right one.
- Use a drop test kit. Aquarium-style KH or total alkalinity kits are inexpensive and give a number in a few minutes. Make sure you know whether the result is in ppm or in degrees, since the units differ.
- Do not rely on TDS alone. Rao’s perspective is that alkalinity is the most useful first water-chemistry number for coffee, and that TDS by itself is not enough to judge brewing water.
- Taste against a control. Brew the same coffee with the same recipe on two waters. If the sour, sharp notes disappear in one and the sweetness appears, you have learned more than a meter would tell you.
Our article on why filtered water improves coffee flavor is a good companion if you are deciding between tap, filtered and bottled.
Adjusting alkalinity at home
If your tap water is very hard and alkaline, the simplest fix is dilution with distilled or low-mineral water. If it is very soft, you can add a small amount of bicarbonate. The numbers are unforgiving.
Daily Coffee News reports that 0.1 g of baking soda in 1 liter of distilled water gives approximately 50 ppm alkalinity as CaCO3, and 0.2 g gives about 100 ppm. That is a worked example of how little it takes: a slip of a tenth of a gram doubles the result and pushes you from a bright cup into flat territory.
A few rules keep this sane:
- Start from distilled or very low-mineral water, so you know the baseline is close to zero.
- Weigh with a scale accurate to 0.01 g, or mix a stronger concentrate and dilute it, rather than trying to weigh a few hundredths of a gram into a single brew.
- Change one thing at a time. Keep dose, grind, temperature and ratio fixed while you change the water.
- Taste, then adjust. Start toward the lower end of the range for light roasts and move up only if the cup is sharper than you like.
The concentrate approach is exactly what we cover in two concentrates for coffee water, with tested recipes for home brewers. And if sour or harsh cups persist after the water is sorted, our one-variable rule for bitter coffee is a methodical way to troubleshoot.
A worked example
Say your water report shows alkalinity of 120 ppm as CaCO3, and you brew a washed Ethiopian ultra-light roast on a filter dripper. It tastes round but muted, with the jasmine and bergamot you were promised barely there. Based on the ranges above, you are well beyond the 20 to 50 ppm that practitioners suggest for most coffees.
Cutting the tap water with distilled in roughly equal parts would bring the buffer toward 60 ppm, a simple dilution estimate you can then confirm with a test kit. Brew again with the same recipe. If the cup now has lift and clarity, you found the lever. If it tastes sharp, move back toward the middle, around 40 ppm.
Now reverse it: a very soft tap water under 40 ppm and the same coffee tastes sour and thin. A small, measured bicarbonate addition is the fix, not a coarser grind or a lower dose.
Our perspective: brew the coffee you were sent
We roast ultra-light and Nordic-style on purpose. The point is to let each origin speak, whether that is a floral Ethiopian or a juicy Colombian, and then ship it on the day it is roasted so it arrives fresh. Water is the last step we do not control, and it is where a lot of subscribers lose the coffee they paid for.
Our advice is practical. Find your alkalinity first, before touching grind size or recipe. If it sits in the low-to-middle range, light roasts will show what they are made of. If it is very high, you will keep chasing brightness that the water keeps erasing. If it is very low, you will keep fighting sourness that no recipe can buffer. Fix the water, then use the feedback you give us on each bag to refine what we send, because personalized selection works best when your baseline is consistent.
And do not let numbers take the fun out of it. A kit, a scale and two glasses of the same coffee will teach you more than any chart.
— Sean
Put it to work with fresh ultra-light coffee
Water tuning pays off most with beans that deserve it. Our subscriptions deliver fresh, single-origin, ultra-light coffee roasted to order, and you can tell us what you taste so future bags match your preferences. Pricing is published per plan: for example, Northern Lip Syncer is listed at $32.99 per month per bag and Duet at $24 per week per bag. Compare all plans, or send a bag to a friend with a gift subscription. Not sure how your brew method interacts with these coffees? Start with how brewing method affects specialty coffee flavor.
FAQ
How do I make my coffee less acidic with water?
Raise the water’s alkalinity. Higher alkalinity buffers more of the acids extracted from the grounds, so the cup tastes less acidic. Do it in small steps, because a change of 0.1 g of baking soda per liter moves alkalinity by about 50 ppm.
Is high alkalinity bad for coffee?
For taste, it can be. Sensory testing found that high-alkalinity water gave flat, chalky coffee with muted acidity, and a peer-reviewed study found reduced fruitiness and complexity as bicarbonate rose. For espresso you can tolerate more, because the drink is concentrated.
Does alkaline water work in a Keurig or other machine?
We could not find a reliable source on the effect in pod machines, so we will not guess. The same logic applies as elsewhere: pH on the label does not tell you the buffer. Check the water report for alkalinity, and follow your machine maker’s guidance on water and descaling.
What is the difference between alkalinity and pH in coffee water?
pH tells you how acidic or basic the water is at this moment. Alkalinity tells you how much acid it can neutralize before the pH changes. For coffee, the second number predicts taste far better.
Can I just use TDS to judge my water?
Not on its own. Scott Rao’s view is that alkalinity is the most useful first number for coffee water, and TDS alone cannot tell you how the water will buffer acids.
Sources
- Water and Coffee Acidity: How to Adapt Your Water for Different Extraction Methods, SCA
- Alkalinity Hardness, Wisconsin Department of Natural Resources
- Demystifying Water for Coffee, Scott Rao
- Boston masterclass announcement and water chemistry, Scott Rao
- Impact of Water Composition on Coffee Sensory Properties, PubMed
- A Practical Water Guide for Coffee Professionals, Part II, Daily Coffee News
- Charting Water for Better Coffee, BWT
