Coffee Refractometers

Okay, so maybe digital coffee refractometers aren’t the most common instruments everyone has in their house. But if you have come to this page, it is probably because you have looked it up on the Internet and therefore have some interest in these devices.

Coffee refractometers are instruments for the analysis of liquids and are commonly found in laboratories and quality control centres. They are as necessary for the good barista (or high profile user) as they are unknown to the general public.

We’ll see what a coffee refractometer is for later on, but for now, we’ll tell you that its measurements are indispensable to know whether a coffee is good or not. Baristas know how important precision is in this work, and that precision is given to you by gadgets such as the coffee refractometer or densitometer.

And you may be wondering, where can I get one of these? Well, not in the bazaar at the corner of your house. Perhaps from specialist electronics shops or laboratory equipment specialists. We also find some refractometers on Amazon, like these:

What is a digital coffee refractometer for?

Coffee machine refractometers are used to measure the TDS of coffee or the Brix of coffee. How can it be that this still sounds Chinese to you? Well, perhaps you will understand it better if we tell you that TDS stands for Total Dissolved Solids, and that Brix degrees measure the amount of sugars present in a liquid (coffee in our case).

By knowing the TDS of the coffee (or degree of solubility, how concentrated the coffee is) through our refractometer, we can know the exact amount of coffee that has been extracted, and the concentration of caffeine it has. This is the measurement most commonly used in the barista’s field, and we will see why later on. With another function of the refractometer, we can also measure the amount of sugars present in our espresso.

In short, these devices are used for two things:

  • To measure the concentration of the coffee (TDS), and to know whether it is more or less diluted in the water.
  • To measure the amount of sugar in the coffee (degrees Brix).

We chose a refractometer for coffee machines: The RCM-1000BT

A coffee refractometer is not the same as one for wine, honey or beer, to name a few examples. There are many liquids in which we may be interested in measuring their concentration or their sugars, so when you buy your barista refractometer, make sure it is a specific model for coffee. Like, for example, this RCM-1000BT from HM Digital.

HM Digital RCM-1000BT Coffee Refractometer (Brix/TDS/Temp) with Bluetooth
  • HM Digital RCM-1000BT Smart Digital Refractometer with Bluetooth technology.
  • Measure, Check, record, and send your Coffee data via your smartphone with HMDigital Smart application for Apple iOS and Android
  • Take Measurement in Brix, TDS, Temp sugar percentage in Brix(%) unit.
  • Measurement Range: Brix: 0.0% ~ 26.0%/TDS:0.0% ~ 23.0%/Temp:0 ~ 70℃
  • Resolution: Brix: 0.01% / TDS: 0.01% / Temp.: 0.1℃ / Accuracy: Brix: ±0.20% / TDS: ±0.20% / Temp.: ±1.0℃

This is a digital refractometer with Bluetooth, which instantly measures both the TSD and the Brix degrees of the coffee, and also the temperature of the coffee. What is the Bluetooth technology of this device for? Well, mainly to record and send the measurements through the manufacturer’s application (HM Digital Smart, available for both iOs and Android).

The measuring ranges of this digital refractometer for coffee makers are as follows

  • Brix degrees: between 0.0% and 26.0%
  • TDS: between 0.0% and 23.0%
  • Temperature: from 0º to 70ºC

Optical coffee refractometers

In contrast to the digital ones, the optical coffee refractometer has a smaller size (as if it were a very thick thermometer) and also a more affordable cost. They only measure the Brix degrees (sugar concentration), not the TDS of our beverage. However, opticians usually have a greater measuring range for Brix than digital refractometers.

How do you use a coffee refractometer?

The coffee refractometer is used in a very simple way. It is another thing to know what to do or how to interpret the data it gives us. It is no use buying a refractometer to measure the TDS of coffee if you then do not use the measurements you get at all. But as far as handling is concerned, the question is very simple:

  • First, using a syringe or similar, take a small amount of espresso coffee and put it in the meter of the digital refractometer (the little metal circle at the top).
  • Press the measurement button to start the process.
  • We wait a few seconds until we see the % solubility of the coffee on the screen of our refractometer.

And that’s it. On the little screen, we will have a number expressed as a percentage (%) that we will call TDS. And now the question is: how do we know the % of extraction of our coffee from this data? It’s very simple: with a calculator and the following formula.

% Extraction = (TDS * Weight of the coffee extracted)/Mass of ground coffee

In case you have any doubts, the weight of the coffee extracted refers to the weight of the beverage, the coffee already brewed. The ground coffee mass is the grams of coffee that you have used or dosed into your filter to brew the coffee (dry ground coffee, of course).

Generally, for any type of coffee, an extraction percentage of around 20% is accepted as correct (not too much above or below that figure).

If you are still not 100% sure how to use a coffee refractometer, this video will help you to dispel any doubts:

Reference values for measuring the TDS of coffee

Do all coffees have the same TDS? Is there a standard or reference value for the universal TDS? No, there is not. It depends on the type of coffee we are extracting. Here are some values that could be considered “normal” depending on the type of coffee we are making.

  • Espresso (normal): around 10%.
  • Long espresso (lungo): about 5-6%
  • Ristretto coffee (short): about 13%.

As you can see, a more concentrated coffee will always have a higher TDS than a more diluted coffee. We notice this immediately in the taste (when tasting the coffee), but what we achieve by using a refractometer is to have an exact, precise and objective figure, which can then be used to know the % extraction with the formula we have seen above.

The relationship between the TDS (the concentration or dissolution of the coffee) and the final % extraction can be seen in the following table:

If you are a barista, you are also interested in this:

Whether you are a professional barista or an amateur, let’s say at an expert level, you will surely need to renew your barista kit with these other accessories, in addition to a digital refractometer: