One of the reasons I love specialty coffee is that you can keep it simple. Learn a simple pourover technique and have some of the best coffee available on the market today. Or you can delve deeper. A lot deeper. Explore origins. Experiment with different brew methods. Switch up the variables. There’s an endless amount of tweaking you can do until you find the formula that makes the best coffee for you.

There is also an endless amount of tools you can buy to help you on your journey. One that recently caught my eye is the Coffee Refractometer.

What is it? How does it work? Do you need it? Will it take your brew game to the next level? Let’s explore.

What is a Coffee Refractometer?

Light behaves in three different ways when it hits a surface. It is either reflected, refracted, or absorbed.

Reflection occurs when light hits a surface and bounces back. This is how you see images in mirrors, for example.

Refraction occurs when light changes direction, or bends, when it moves from one material to another. This is why, for example, it looks like light bends when it hits water, or why it looks like the straw in your glass of water bends at the surface.

Some surfaces neither reflect nor refract light. Instead, they absorb the light. Causing the surface to heat up. Try to walk to your car barefoot on a Dubai summer day and you’ll know exactly how surfaces that aborb light heat up.

Refractometers are scientific tools that measure how light bends (i.e. refracts) as it moves between the air and the liquid. A Coffee Refractometer performs exactly the same function and measures the Total Dissolved Solids (TDS), allowing us to calculate the extraction yield.

What is TDS?

The roasted coffee that you grind and then dissolve in hot water to make your coffee is referred to as the Total Dissolved Solids (TDS). It is effectively a measure of the amount of coffee in your coffee. When you’re able to define the TDS in your cup, you can calculate the Extraction Yield in your brew using the formula:

Extraction Yield % = Brewed coffee (g) TDS (%) / Dose (g)

What is Extraction?

Extraction, in coffee terms, refers to the act of pulling soluble compounds out of coffee beans by using water. Put another way, if you’re pulling a shot, the extraction is all of the stuff that was in the grounds in our portafilter basket, that’s now in the cup. The amount of dissolved solids in that cup (i.e. the TDS), in proportion to the amount of water that was used, is how we determine the strength of our coffee. For example, if there were more dissolved solids in that same volume of water, it would be a stronger cup of coffee. In other words, the extraction has a huge impact on a coffee’s flavor, so it’s a useful piece of information to know.

We measure the amount of dissolved solids, the TDS, with a Coffee Refractometer. The Coffee Refractometer shines a laser through a sample of our coffee to determine what percentage of the sample is dissolved solids, i.e. to determine the TDS. If we know the TDS, we can then calculate the Extraction Yield (using the above-mentioned formula).

So what?

Experts say the ideal extraction yield for drip coffee is between 18% and 22%. Based on a TDS percentage of between 1.15 and 1.35. The greater the quality of the coffee, the higher these numbers go.

Why Use A Coffee Refractometer?

Brewing a great cup of coffee is a skill. A skill you can learn. The bigger challenge is, however, brewing a great cup consistently. That’s where the Coffee Refractometer comes in handy. Once you’ve brewed an exceptional cup of coffee, you can use the refractometer to measure its TDS and extraction yield. That way, you’ll know if you’ve reproduced it precisely in the future.

How Do I Use A Coffee Refractometer?

That’s the simple part. Just add a few drops of brewed coffee to the refractometer’s sample well, and it will report a TDS value. Repeat this process using different recipes while tasting until you land on the most delicious cup. Then you’ll know the optimal extraction yield for your coffee.

Do you need a Coffee Refractometer?

Not at all. Your taste buds are still an effective (and cheap) way to measure extraction. But if you’ve got the budget (most are quite expensive) and want to be more scientific in evaluating your brew, Coffee Refractometers are a fun way to learn more about your coffee and achieve more consistently delicious brews.

Any reputable reseller of coffee equipment, like Brewing Gadgets, for example, will stock them. The one pictured below is by DiFluid. And you can pick one up here at a surprisingly good price.

The DiFluid Coffee Refractometer

Have you used one before? Are you planning on getting one? Let us know in the comments below. And don’t forget to sign up to be the first to hear any FLTR news and for a chance to win exclusive subscriber giveaways.