Let’s Talk About TDS, and MoJoToGo’s Coffee Lite Mode
What makes a cup of coffee taste?
Not taste good, not taste bad, just… taste.
Polyphenols! And acids! And fats! And carbohydrates! And… well, who knows. Plenty of people, actually, but how much of that is relevant to making a good cup of coffee? Dictation of taste comes down to two main factors that we can measure: extraction yield, and total dissolved solids. Or, if you’d like — how much we’re extracting from the coffee, and how much of the total brew is made up of those solids we’ve extracted.
Coffee is made up of around 30% soluble solids. When we talk about extraction yield, we’re talking about how much of those 30% soluble solids we’re dissolving into hot water to create coffee. It has been generally established that 19% extraction yield is where coffee tends to taste the sweetest.
The overall drink that we look at as brewed coffee is about 98.5% water. It’s that small, critical amount of total dissolved solids (from hereon referred to as TDS) that dictates the concentration of the coffee. And while 19% has been established as the preferred extraction yield (the overall accepted range being around 18-21%), TDS is a preferential metric. As long as you’re hitting that extraction yield that we’re looking for, any range of TDS from 1.2%-1.7% as an extreme example will taste sweet. Often thought to be fairly regional according to preference (Specialty Coffee Association of America preferring around 1.3%, Specialty Coffee Association of Europe preferring around 1.4%, Nordic Coffee Association preferring around 1.5%), TDS has been fairly ignored in this past year or so of heavy extraction measurement in specialty coffee — extraction yield has been the main concern.
But in this Twitterverse of knowledge transfer and recipe sharing, we never talk about what our target TDS is. And this is mainly because most of us don’t know what it is. We look at a coffee to water recipe and brew with it until it tastes sweet, adjusting the grind, temperature of water, etc. But knowledge of what the target TDS range for a shared Chemex recipe greatly determines what recipe we’re actually shooting to use.
If I told you to use 32 grams of coffee for 450 grams of water at 200ºF, you could take that recipe and brew with it. But if you knew that this recipe relies on 1.60% TDS in order to reach a 19.61% extraction yield, you’d have a better advantage towards hitting that extraction yield. You’d know that a longer contact time, or slightly finer grind is going to assist you in getting a higher concentration of soluble solids in the cup, possibly more advantageous than just hoping your standard grind/contact time would be suitable.
Our industry Gold Cup Standard relies on using 60 grams of coffee for 1 liter of water. But this recipe assumes about a 1.3% TDS. Whenever I see someone balking at a 70 gram per liter ratio and saying it’s wrong, I want to sit them down and try and talk about extraction science. This isn’t a “bad’ or “wrong” ratio. It’s a ratio that assumes a higher TDS concentration in order to achieve a tasty extraction yield.
Now then, we do have a slight issue when we use 70 grams per liter, and one doesn’t adjust things like grind size or contact time. If we use a higher coffee to water ratio and don’t manipulate our brewing variables to accommodate it, we end up underextracting the coffee.
Sure, this is a danger, but so is using too little coffee. Many times people have tried to maximize their coffee to water ratio and use as little coffee as possible to achieve a tasty cup. But what this means is that the recipe necessitates a low TDS in order to achieve a tasty extraction yield. Otherwise you run the risk of overextracting the coffee and bringing out the bitterness that overextraction yields.
So if we aren’t looking at, discussing, or acknowledging the power that TDS has over the recipes that we’re using, we’re cheating ourselves out of one half of the measurable constants that we have readily available to us to use as a discussion basis.
And this isn’t even considering the affect that TDS can have on the flavor of the coffee. With a low TDS, the flavors we’re looking for — say pear, baking spice, and hazelnut — may be harder to pick out. With a high TDS, we’re cramming those flavors into the coffee to the point of being very intense and sometimes overlapping to a detrimental point.
That isn’t to say you can’t achieve a sweet cup at either end of the spectrum. It’s totally possible. What it means, however, is that TDS is what we can use to manipulate the flavors of the coffee that we’re presenting. Or the brew method we’re using to highlight those flavors. Personally, I’m a bigger fan of a 1.4% target TDS range for V60 brewing in order to bring a lingering space between flavor notes, while a 1.55% target TDS for an Aeropress seems to bring a punchy flavor explosion to the palate.
Yes, it’s all preferential. That doesn’t mean we shouldn’t talk about it. In fact, it’s what we need to talk about. Extraction yield is an introduction to coffee tasting. But if your coffee is tasting sweet, we need to move past that quickly and talk about why it’s tasting sweet, which is a combination of the amount of coffee used, the amount of water used, and the total dissolved solids in the cup — all of those factors are what we use to determine the extraction yield.
One thing I’d like to mention to round out this discussion is the availability of an iPhone app called MoJoToGo. It’s the portable version of ExtractMoJo, a software suite designed to help us measure our extraction yield in conjunction with a coffee refractometer that gives us that data by calculating coffee in, water in, and total dissolved solids.
The application’s $30 price tag is pretty reasonable for being able to scientifically interpret data in terms of extraction, but I found another use for it when at home. I used MoJoToGo to compute basic brew formulas for all my brew methods. Start with a target TDS, plug in the amount of water you want to use to dictate how much coffee you want to brew, and slide along the amount of coffee to use until the extraction yield slider hits your preferred target. It’s simple, easy, quick, and helps interpret new coffee recipes that we’re sharing.
Now the application also has a Lite Coffee mode. It’s only $5, and has a few things disabled — like the TDS slider, but works the exact same way. You’re able to choose your target TDS from the preset preferences, plug in your water data, then slide your coffee data until you find the right extraction yield. There’s even the ability to add a bunch of correlating data to your recipe and email it off to other people.
Okay, it’s a bit of a shill — but I like the program a lot, and it has really, REALLY helped me understand the science of coffee extraction and manipulate the coffee recipes I’ve been using to develop the tastiest coffee I’ve ever brewed at home.
What it represents, however, is a way for small shops to help introduce themselves to better recipes and smarter brewing. If you don’t have the budget for a refractometer yet, Lite Coffee mode will give you most of the tools you need to develop a good extraction yield by taste. Now some people may have issues with the software and with discussing coffee only in terms of extraction yield and TDS. A lot of folks are decrying this scientific pursuit and only want to talk about taste.
The issue is that when we talk about taste, and subsequently dialing in a coffee by taste, we’re ignoring the fact that we’re manipulating these two variables in order to find a taste we like. Why not eliminate the guessing work? We’re still dialing in by taste, but if someone’s offering you a GPS device for navigating a city you think you’re pretty familiar with, you might as well take it to help you plot your course. It’ll help you remember that Madison Street is a two way until you hit Dearborn, and then it turns into a one way, and you have to circle around the block in order to get where you want to go. And believe me, $5 for a GPS device is a pretty good deal.
For full disclosure, I’ve had many conversations with Vince Fedele of VST Software, who invented MoJoToGo, and helped develop the coffee refractometer. He’s been a great resource for coffee discussion, but we don’t always see eye to eye on a certain number of coffee brewing topics. It’s because of my enthusiasm for using the iPhone application as a recipe resource instead of just as a measurement tool that Vince asked me to help test the Lite Coffee mode.
You can take that how you will, but in no way did my involvement in testing the software affect my eagerness to write about how helpful of a program it is.
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