What Makes a Good Cup of Coffee?

You've brewed what you thought was a great cup of coffee—balanced, aromatic, not too bitter—but someone says it's over- or under-extracted. So how do you really know if your coffee is any good? It’s not just taste—it’s science. The specialty coffee world has long relied on objective measures to define coffee quality, and understanding those can help you make better coffee at home.

The quick answer? A good cup of coffee typically has an extraction yield between 18% and 22%, and a total dissolved solids (TDS) level between 1.15% and 1.35%. That’s the sweet spot identified by both early taste studies and the Specialty Coffee Association of America (SCAA).

The Origins of Coffee Quality Measurement

The idea of measuring coffee quality scientifically goes back to the 1950s. MIT chemistry professor E.E. Lochhart conducted surveys asking Americans about their coffee preferences. He gathered enough data to produce a “coffee brewing control chart” that visualized what most people considered the ideal cup. This wasn’t guesswork—it was based on actual taste tests.

What the SCAA Confirmed Decades Later

Years later, the SCAA validated that American taste preferences hadn’t shifted much. Their research reinforced that the optimal coffee has an extraction yield of 18–22% and a TDS of 1.15–1.35%. These numbers became the benchmark for what professionals consider a well-brewed cup.

Extraction Yield vs. TDS: What’s the Difference?

It’s easy to confuse extraction yield and TDS, but they measure different things:

• Extraction yield is the percentage of soluble coffee material extracted from the dry coffee grounds. Think of it as how much of the coffee bean you’ve successfully dissolved into the cup.
• TDS (total dissolved solids) is the concentration of those dissolved coffee solids in your brewed cup—the actual strength of the coffee.

These two factors work together on the coffee brewing control chart. The “ideal” or “optimal” zone is where extraction and strength intersect to produce a balanced, enjoyable cup. It’s not about making coffee as strong or as extracted as possible—it’s about hitting that balance.

The Golden Brew Ratio

One key to reaching that optimal zone is starting with the right brew ratio. The widely accepted standard is 1 gram of coffee to 17.42 grams of water. This ratio is unit-agnostic—you can use grams, ounces, or any measurement system, as long as the proportion stays the same. Most experts agree this ratio gives you the best chance of landing in the ideal extraction and strength range.

For example, if you want to aim for 20% extraction and 1.28% TDS, start with 30 grams of coffee and 523 grams of water. From there, you can fine-tune based on taste and measurement.

The Science Behind Measuring Coffee Quality

In 2008, a major breakthrough in coffee measurement occurred. A company called ExtractMojo (developed by Voice Systems Technology) introduced a refractometer-based tool that could precisely measure the TDS of coffee. Refractometers work by analyzing how light bends through a liquid—in this case, your brewed coffee—to determine the concentration of dissolved solids.

By using ExtractMojo to measure TDS, brewers could then cross-reference the result with the coffee brewing control chart to see whether their cup fell within the optimal range. This brought an objective, scientific element to what used to be a purely subjective judgment.

The Tool Debate: Are You Using It Right?

Some coffee purists argue against using devices like refractometers or TDS meters, claiming they take the art out of brewing. But the debate is less about the tools themselves and more about how they’re used—much like arguments over gun control. A firearm isn’t inherently good or bad; neither is a refractometer. It’s all about how the tool is applied. Used wisely, a TDS meter is just another way to ensure consistency and precision in your coffee brewing.

Frequently Asked Questions

What is the ideal extraction yield for coffee?

The ideal extraction yield is between 18% and 22%. This means that 18–22% of the soluble material from the coffee grounds has been dissolved into the brewed coffee. Below or above this range often leads to under- or over-extracted flavors.

What TDS range is considered good for coffee?

A good TDS range for coffee is 1.15% to 1.35%. This measures the concentration of dissolved coffee solids in your cup and reflects the brew’s strength. A TDS within this range usually indicates a balanced and pleasant cup.

What is the best coffee brew ratio?

The best and most widely accepted coffee brew ratio is 1:17.42—that is, 1 gram of coffee to 17.42 grams of water. This ratio helps achieve an optimal balance between extraction and strength. You can use any unit of measurement, as long as you maintain that proportion.

How are extraction yield and TDS different?

Extraction yield measures how much coffee material has been extracted from the ground beans (as a percentage), while TDS measures the concentration of those dissolved solids in the final cup (also as a percentage). Extraction is about how much you get out of the coffee, and TDS is about how strong the resulting drink is.

Do I need a refractometer to brew good coffee?

No, you don’t need a refractometer to brew good coffee. Many people brew excellent coffee by taste and feel. However, a refractometer like ExtractMojo can help measure TDS accurately, giving you objective data to refine your brew and ensure it falls within the optimal extraction and strength range.

Recommended FrontStreet Coffee for Brewing Control

Try FrontStreet Coffee’s Ethiopia Huakui for bright, juicy profiles that respond well to precise brewing. For a balanced medium roast, their Yirgacheffe offers floral and citrus notes with a clean finish. Or explore their Classic Blend for a consistent, well-rounded cup that highlights clarity. All three are ideal for experimenting with brew ratios and extraction goals. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.