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Of Goldilocks, Lasers, and Total Dissolved Solids.

Of Goldilocks, Lasers, and Total Dissolved Solids.

Over the last few years, the coffee I brew at home has become less developed; any pleasant brightness of acidity has faded and the sweetness has dulled, producing a woody taint.  When the tasting notes on the box say "Jasmine, Nectarine, and Pure-Joy," that magic just isn't there once I get home.  

No, this isn't a poorly-veiled metaphor about the mundane quality of domestic living.  This is a real, legitimate, first-world problem.  

I'm sure this gradually flattening flavor from a home-brewing setup is familiar to readers, but have no fear, science is to the rescue!

The Scientific Method

Question:  Why does my coffee suck?

Hypothesis:  If I use the same water and ratio of water to coffee, but test my grinder against a better, newer grinder (a fresh set of burrs), my grinder will show inadequate total dissolved solids (TDS) while the newer grinder will have a more satisfying TDS reading (read “taste WAAAAY better”).

Experiment: I’ll use a V60 to analyze flavor development (and by flavor development I mean solubles and taste) at various levels of extraction.  Some constants that I don’t need to experiment on include water (I've got an RO system that puts out a set parts per mileteter, and it is right where I want it… I’ve tested it… that’ll be a whole different blog-post), ratio of water to coffee (I've always used a gram-scale for the amounts of both coffee and water poured on that coffee), and I've been using the same grinder for about five years.

Variable: Though the grinder isn't a variable, the burrs within the grinder don't last forever... nothing golden says, Pony Boy.  This seems to be the main culprit in my flat coffee.

Tools To Collect Data-Points: Refractometer and tastebuds.  The refractometer is a tool that fires a laser through a liquid (in this case, coffee) and then measures the bend in the laser's light to measure the total amount of dissolved solids in that liquid's content.  In the case of coffee, we're measuring how much fat, oil, and coffee (at a micro-level) has pulled out of the grounds through the brewing process into my cup of coffee. In the picture below, the boxy-grey object with the big blue lid on top is the refractometer, and the three cups are the resulting V60's we made.  

Put more simply, the refractometer is a tool that is helping us measure with objectivity and consistency how "strong" the coffee is rather than just saying “that tastes better.”

Analyze & Report: To make a long story short, my grinder was all over the place in how much TDS were in each brewing.  I couldn't duplicate the same results with the refractometer, and the taste was suuuuuub par when compared to the newer grinder (the new grinder was very reliable from brew to brew in terms of TDS readings).  

At the end of the day, my original question question doesn't take a refractometer to answer, but the refractometer does give me a data-point to analyze, rather than just saying "this doesn't taste good."  It validates my very unscientific sense that something is amiss.

Outcome of Test:  I got myself a new grinder!

A New Hypothesis

The best use for the refractometer is to fine-tune my new grinder to an optimal range of TDS.  That's what we use it for at the cafes, at least.  We want to make sure from cafe to cafe we can hold our baristas to a scientifically, data-driven goal.  We want them to know when they've reached their goals by collecting data as well as consulting their own palate.  

With all that in mind, let's set up a quick, NEW question and hypothesis to use this tool to make my coffee-experience as excellent as possible.  

Especially with a new grinder, I tend to go over-board and grind a little extra-fine because... well, because I can.  So...

NEW Question: Why does my coffee taste too sharp... a little too acidic?  

NEW Hypothesis: My ratio of coffee to water is what I want it to be for the “strength” that I like.  My water is of a comparable particulate level that it always has been.  The roasting of the coffee I like has been developed appropriately and is consistent.  This leaves the grind fineness, and I believe I can grind coarser than I typically do at home and still fall in the range of desirable TDS.

Here's an image of the grind-coarseness we used to test three different grind settings:


Here's what data we found from the coarsest one:
Total Brew Time (TBT): 1 minute and 41 seconds.
Total Dissolved Solids: 0.86
Extraction: 13.27% of the liquid is coffee.  That's pretty low when you're talking about a pour-over method of brewing coffee.

Here's what data we found from the finest one:
Total Brew Time (TBT): 3 minute and 3 seconds.
Total Dissolved Solids: 1.61
Extraction: 25.01% of the liquid is coffee.  That's going to taste like the stuff your grandpa drank and often told you would "put hair on your chest!"

Here's what data we found from the medium one:
Total Brew Time (TBT): 2 minute and 15 seconds.
Total Dissolved Solids: 1.32
Extraction: 20.46% of the liquid is coffee.  That's the sweet spot we're looking for.

Analyze & Report: As with Goldy Locks, it was the medium option that was just right.  Its flavor was balanced because the uniform surface area that newer grinder provides gave us a consistent extraction from the coffee as it went through the V60.  Putting the two hypotheses together, we can make the statement that the newer grinder performs better, and on top of that, I should be using a slightly coarser setting than I had in the past.  This provides the desired TDS (there's enough coffee dissolved into my water), and by letting there be a lower surface area accessible to the water in the brewing process, I am pulling out a more balanced, rounder cup.

Hooray science!  Hooray coffee!  Hooray refractometers!!!