While searching in the dark for answers, people will develop the perception that having deeper understanding to the specifics gives more information and better grasp in the mastery of the art. That happens to be the same for coffee that has driven huge interest in the past few years as users have higher expectation and cafe hopping becomes a trend.
One of the variables that many people in the trade measure is the coffee TDS, normally measured with a refractometer.
What this device do is it measures the Total Dissolved Solids. As the name implies, it practically measures how much dissolved matter is extracted in your coffee. The general association people relate to is the bigger the number the better is your extraction. You can probably guess that this is a rudimentary assessment that don’t picture much details.
The measured coffee TDS is like the amount of cholesterol measured in your blood. Having a big number may mean sometime, more associated with its viscosity. It does not describe what’s exactly in it. Just like cholesterol, there’s high and low density lipoprotein that are good and bad for anyone. People with the data generally don’t know what they can really do or what it really means. On the other hand, following such data can be misleading and induce confusion.
To give you an idea, in the coffee there are receptors in the colloids that block off bitterness. They are plentiful in the beginning of the extraction and depletes quickly in less than 20 seconds. Following that, astringents start to appear. So having a high TDS doesn’t tell you how much of the good or bad you get. That’s why many baristas know that coffee gets more bitter as they extract longer. That’s why the Italians prefer Ristretto which is only a sip of 15ml concoction done in 20 seconds. They have drank so much and enough to understand that the best comes from short extractions.
So if you are an aspiring barista, will I suggest that you splurge on a refractometer and hone your coffee knowledge? We think that the device might be more useful for coffee roasters to get a gauge if their roast is on spot. The darker the roast, the more oil and carbon dioxide is formed in the coffee. Judging from the color of the roasted coffee, is hardly accurate. Following programmable roasting profiles may be good, but any changes in the amount of coffee used or different batches of coffee with slightly different condition. Can end up with different results. Measuring the coffee TDS may help to give the roaster a little bit more assurance. Still, it won’t tell you accurately what’s in it. It can be favorable volatile organic compounds or astringents.
The correct way to measure in the lab is to dry up the coffee and do analysis on what’s left. This is probably a job too big for most. The easiest test to measure your coffee, is to use your tongue and perform a taste test. If they taste good, it doesn’t matter what’s the coffee’s TDS.
