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Have you ever walked into a café and seen the barista in the middle of a crazy science experiment?👨🔬
At least that’s what I felt like the first time I saw a barista taking a coffee sample with a syringe and placing it on a tiny machine… I wondered: What on earth is going on?! I quickly found out that the barista was measuring the TDS of their coffee using a device called a refractometer. Today we’ll dive into the subject of refraction in coffee brewing!
What is TDS?
By now you probably know that a cup of coffee is more than 98% water and the rest is dissolved solids from the ground coffee. A refractometer is a device that helps measure how much of the brew is the actual dissolved solids from the coffee and how much is water, and this is key if we want to understand coffee extraction on a higher level. This is called TDS (Total Dissolved Solids).
In other words, a refractometer measures the concentration of a cup of coffee!
Why measure the TDS in your coffee?
The TDS of a brewed coffee gives an indication of well we’ve extracted our coffee, because once we know the dose, brew weight and TDS we can calculate how much of the coffee bean’s mass we have extracted. As a general rule, a tasty extraction should be somewhere between 18 - 22%. If we go lower than that, the coffee usually tastes under-extracted or watery. If we go above the 18 - 22% range the coffee usually tastes over-extracted and bitter.
A trap to watch out for!
If you ever get to try a refractometer, watch out for the trap of blindly following the numbers. Sometimes you might brew an amazing brew, but the refractometer gives you a TDS that suggests that your brew is ‘’outside’’ the recommended range, leading you to change your recipe and actually making the coffee taste worse just to get the ‘’right’’ TDS. Don’t fall for this trap! Instead, you should only make adjustments based on the taste of the coffee.
A refractometer is by no means necessary to brew amazing coffee, but it can sometimes help. An example is if you struggle to get a brew to taste good and have a hard time troubleshooting - a refractometer can guide you to help you to find the right grind.
Who should use a refractometer?
A refractometer is beneficial for cafés and roasters as it provides an reference point to keep track of consistency. As an example, one can measure whether all baristas working in a café achieve the same extraction, therefore providing the guests with a similar taste experience.
Is it worth the money?
For coffee roasters and cafés, a refractometer is definitely worth the money as it’s a tool that will help with quality control! ✅
However, for the home brewer I personally think it’s a bit overkill unless you have high ambitions to compete in coffee competitions. The reason being that they are quite pricy and are not essential to brew amazing coffee, and the benefits they provide for businesses don't really apply for home use.
To sum it all up, refractometers are a useful tool the coffee industry. Measuring TDS can help you better understand coffee extraction, and help you achieve consistency within your café or roastery. Just remember to let the taste of the coffee guide you first, not the TDS measurement of the brew 😉
— H.S
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