Let's dig into Total Dissolved Solids (TDS) in coffee, the objective measurement of a brew's strength.
What is TDS?
We’ve all been there: you take a sip of coffee and it tastes "too strong" or "a little watery." But in the world of specialty coffee, those terms have specific, scientific meanings. If you’ve ever wondered why your coffee sometimes tastes like a masterpiece and other times not-so-much, the answer lies in three letters: TDS.
Total Dissolved Solids (TDS) is the objective measurement of a brew’s "strength." Specifically, it represents the actual coffee particles that have been dissolved into the water.
When we talk about TDS, we are looking at the concentration of coffee solubles in your finished cup. It’s the difference between a thin, watery liquid and a heavy, intense beverage.
- Low TDS: Results in a brew that feels weak, watery, and under-developed.
- High TDS: Results in an intense, heavy, and potentially "muddy" mouthfeel.
The Goal: Finding the "Sweet Spot"—that perfect intersection where clarity of flavor meets a satisfying body.
The History
The standards we use to judge a "good" cup of coffee aren't just guesses; they are rooted in decades of data.
In the 1950s, Ernest Earl Lockhart, an MIT professor and Director of the Coffee Brewing Institute, set out to solve a mystery: What do coffee drinkers actually like? Lockhart mapped out the parameters of "acceptability" based on thousands of consumer preferences. His research was so comprehensive that it remains the backbone of the Specialty Coffee Association (SCA) Brewing Standards we use today. Whether it’s 1955 or 2026, the human palate generally seeks the same thing: balance.
Extraction vs. Strength: Understanding the Difference
To master brewing coffee, you have to distinguish between how much you took out of the actual coffee bean and how many coffee particles are in the water.
1. Extraction: The Yield
Extraction is the result of water taking dissolvable material from coffee. Roasted coffee is roughly 30% extractable (soluble) and 70% non-extractable (insoluble fiber).
- Under-extracted: Tastes sour and astringent.
- Over-extracted: Tastes bitter with a long, unpleasant aftertaste.
- The Sweet Spot: Aim for 18%–22% extraction. This is where natural sweetness shines.
2. Strength: The Concentration
Strength is the measurement of the concentration of those solubles in the water.
- Too Concentrated: Tastes ashy, smoky, or pungent.
- Not Concentrated Enough: Tastes papery, dry, or "peanutty."
- The Sweet Spot: For U.S. coffee drinkers, the "Golden Ratio" for strength is typically between 1.15% and 1.35% TDS
Image based on SCA Brewing Control Chart
Quality vs. Preference: Why We Like What We Like
It is important to distinguish between Quality, an objective measurement of preparation, and Preference, a subjective liking of one thing over another.
Think of it like clothing: A pair of jeans can be high-quality because of the denim and stitching, but you might prefer slacks for the style. In coffee, a brew might be objectively high quality (perfectly extracted from ripe, fresh beans), but you might prefer a different origin or roast profile based on your memories and environment.
Because humans associate flavors with experiences, we can actually prefer lower-quality items (like stale candy or burned toast) because of the emotional response they trigger. However, the science of TDS gives us a map to ensure that—regardless of the bean—the preparation is flawless.
Measuring Success
How do we know if we hit the mark? Professionals use tools like Refractometers (which measure the refractive index of light passing through the liquid) to obtain a digital reading of TDS.
By measuring the TDS and knowing our coffee-to-water ratio, we can calculate the extraction percentage. If the numbers fall within the 18%–22% extraction and 1.15%–1.35% strength ranges, we’ve officially hit the Golden Ratio.
Three refractometers set up to measure the TDS in competition coffee's at Counter Culture Coffee's Brewlette competiton in New York City.
Ready to geek out on your own brewing methods? Whether you’re using a French Press or a V60, remember: if it tastes "off," you’re likely just a few TDS points away from perfection.
Check out our brewing guides to get started on your next brew!
