Coffee Refractometer - How to use and Why

In short, coffee refractometer is a device which helps you to understand how well coffee is brewed. And it shows you one number which says a lot.

It does it by measuring the concentration of liquid. Meaning, amount of soluble material in it. And this helps you to adjust your recipe faster. 

Of course, it's possible to make a great cup of coffee with just the experience and taste assessment. But there are cases when it will be unreliable and not enough.

Why we need to know concentration in coffee

It allows to understand, how well coffee is extracted. And if it seems that technically, the number seems fine, then you know what exactly to change in order to improve the flavor (usually I target 1.35% on a refractometer when brewing pour over coffee with 1:16 ratio, like 20 g of coffee 320 g of water).

If I measured my coffee and it shows the number lower than 1.3% - I know, that it's better to make the grind size smaller. Or use some other parameter to improve the extraction.

If it's 1.5% - I know, that it's possible to make the flavor "cleaner" by making the grind size bigger.

If it shows 1.35% and the coffee tastes weirdly - I simply know that I need to pay a lot of attention on flavor and it will give understanding the next move. 

But we can simply taste it, right? 

Partially. If you are a calibrated person, sometimes you can guess correctly the "intensity" or TDS (total dissolved solids) of coffee.

Calibrated - meaning you've tried different intensity and remembered the number for such intensity. So that you know how well extracted coffee should taste like.

But it happens a lot that if coffee is too fresh - you will not perceive the flavor accurately. Also, texture of the coffee can trick you. If coffee is "drying" - it could be both, under and over extracted.

And simply thinking that "if coffee is sour it is under extracted" will not help you either. Because it can taste relatively balanced but still have a low extraction.

Skewed perception

Besides fresh coffee which is hard to assess with taste buds, the taste buds themselves should be ready for work. You can't assess properly first cup that you drink each day. At least most people can't. You need some coffee to "turn them on". 

Also, if you've tried some food - it will skew it a lot. Like, you can sometimes perceive only acidity in coffee, without sweetness or bitterness. So it will be impossible to tell if coffee is OK or not.

It helps you to learn

Coffee is a living product. It always changes. And spotting it's behavior is a nice skill that needs to be developed. Of course, you still can experiment with trying to brew it using different grind sizes. It's a nice thing. But it's way easier to have a numbers to confirm your theory. 

Accuracy, standard

The most important part. If you go to a coffee shop, you expect good results. But each human is different. Some may like more acidic coffee, some - strong and intense. That's why it's better to have a reference to what is considered to be "good". 

There is some international coffee organization which studied what extraction of coffee is usually perceived as tasty. And it's a range within 18 to 22%. Out of around 30% which we can get from coffee beans. 

Which in terms of refractometer (and ratio 1:16.67) means around 1.3-1.55% range). That's the numbers which it shows to you.

So if you want some stability in your coffee shop - you can ask baristas to target some extraction every shift. 

How exactly does coffee refractometer work

Technically, it measures the reflected light. We're not going to go deep, I'm not an engineer. Instead, just understand that it measures the amount of soluble material in the liquid. And shows the percentage of them.

Example: TDS (total dissolved solids) of pour over coffee is 1.25% (yes, it is measured in percentage).

Which means in 250 g of coffee we have 3.125 g of soluble material which we extracted from the coffee beans. (250 g of coffee * 1.25 / 100). So that we understand, that from 18 g of coffee that we used, we extracted around 17% from our coffee. 3.125 / 18 * 100 = 17%. 

And we know that we can extract around up to 30% of the coffee bean weight (meaning, from 100 g of coffee we can get 30 g of "flavor" and the rest will be cellulose in which the soluble material is stored).

Result: Meaning, we did a relatively good job brewing this coffee. But not perfect. 

How to calculate extraction

Again, refractometer shows us the % of soluble material if liquid (coffee).

And we have two ways to calculate it: install some app (some shady one which collects a lot of your personal data for no reason like difluid cafe) which will help you to simplify the process.

Or calculate it manually. Though, I rarely calculate the extraction at all, % says a lot.

Anyway. Example:

Dose of coffee: 18 g

Dose of water: 300 g

We brewed the coffee using 300 g. But in the cup we got around 270 g as the result. Because some is retained in coffee. So we use 270 g for calculations (the actual weight of the liquid).

We measure the TDS using the refractometer. And it shows 1.7% for some reason. 

We use the formula to get the amount of actual soluble material in grams:

Actual amount of liquid (270 g) * TDS (1.7%) / 100

270 * 1.7% / 100 = 4.59 g of soluble material from coffee

Extraction = Dissolved solids (4.59) / dose of coffee (18) * 100

4.59 / 18 * 100 = 25.5% of extraction.

Yes, it's that simple.

Extraction, Extraction balance, Flavor

You see the problem now. We extract some coffee, but not all. And we don't know what 15% out of 30% we extracted. Maybe it'll be tasty, maybe not. That's why even with calibration people will struggle to understand what's wrong.

I usually adjust the grind size first to nail the extraction. So that it is 1.3-1.4%. And from here, usually coffee is perfect. Because I use Hybrid flow pour over technique. 

But if I use a regular recipe - I think about the brewing time. If it shows 1.3% but the flavor is "muddy", "dull", "dark" - it's a sign that it's better to brew coffee faster. In most cases.

But without knowing the number from refractometer it'll be like "I will play with the grind size and then write a bad review to a coffee roaster because it's his fault, coffee is bad".

Pour Over and Espresso

I don't use refractometer for Espresso. It's way easier to judge the shot by the aroma, crema color etc. In Pour Over - it's harder to do that, so that's why I use the refractometer quite often. Especially if the coffee is not brewed well from the first try.

What if I don't have a refractometer

Easy. Pay attention to the body and the aftertaste. If aftertaste is "thick" and pleasant - you did a great job. If coffee is "thin" in flavor - you can make the grind size smaller until you get a good lingering aftertaste. 

And if coffee becomes more acidic when cooled down - you definitely need to make the grind size smaller next time. 

If coffee feels burnt and drying - it could be low extraction (again, make the grind size smaller) or too high water temperature. Especially if some "sharpness" is present. "Aggressiveness" in flavor.

What refractometer to choose

I have some experience only with some no name one (which isn't accurate at all), VST (kind of outdated but still reliable... costs A LOT) and DiFluid R2 Extract (which DiFluid sent me to make a video review, but I wanted to get it for myself anyway). Ah, no, I also used Atago Barista for a couple of times. It was kind of slow, but they all somewhat slow.

I compared VST vs DiFluid R2 during Comandante c60 vs Kinu m47 test - both showed the same result (within 0.01% accuracy). But they measured differently. First of all, DiFluid shows the temperature of the coffee sample. So that you see when the result is more or less stabilized (you can't just pour coffee and get the result, sample need to be at room temp).  

VST started to show from small TDS while DiFluid start to show from high TDS. And when sample is cooled down - they both show the same info. 

But a good thing that we can do a multiple tests on DiFluid and see the graph. So that we sure that there is no need to wait for it to cool down even more. Though, again, it will require for you to install their app. To update the firmware, adjust the parameters. So it's better to have a separate phone for such apps if you care about privacy. 

Anyways, device is small and useful. Hopefully I'll get an updated version with the aluminium dish (which helps to cool down the samples faster). For home use - it's 100% enough. Even for coffee shops, should be reliable enough.

And review for members of the channel:

Do I actually use it?

Yes. It helps a lot when I don't know where to move with the recipe (happens once a week at least). Or when I don't sure how far should I push the grind size (happens once in a couple of days). And most importantly, helps to develop new recipes and be sure they're reliable and stable. By spotting some coffee behavior with different coffee filters etc.

If you struggling with getting the flavors which are mentioned on a coffee bag - definitely a nice thing to have.