Hardness?

Been plowing through my latest acquisition, “The Professional Barista’s Handbook.” There are three pages devoted to tea.  That’s two less than the section on water, and one-fifth of the size of the milk chapter.  I’m not sure what to think when author Scott Rao writes, “It would be nice to see a few more cafes treat their tea programs with a fraction of the respect they give their espresso programs.”

But I knew this before I got the book.  From the introduction: “My coffee library was chock-full […of nuts? No,] of colorful descriptions of brewing styles, growing regions, and recipes, with a few almost-unreadable scientific books mixed in.  I would have traded in all of those books for one serious, practical book with relevant information about making great coffee in a cafe….This book is my attempt to [create that book.]”  Rao could be talking about my tea library.  Coffee is still way ahead: tea doesn’t seem to have the culture of tech-oriented coffee geeks debating the finer points of chemistry.  Now coffee has Rao’s books, and tea doesn’t have that either.

Before I resume complaining about the dysfunctional resistances to scientific empiricism tea has culturally and historically inherited, let me say Rao’s book is very useful.  First, it’s motivating to see other people successfully using science to make better beverages, and making a living doing so.  Second, I now have a solid theoretical understanding of coffee, while never having groomed a portafilter.  Tea work is hard to come by, and now I have a better chance of getting hired at a javacentric cafe if I need extra shifts.  But most importantly, there is knowledge in this book that is generalizable to tea.

A large portion of it concerns water.  I’ve already written about water here and here.  We know that a water’s total dissolved solids have the largest effect on its taste.  A couple of my buds have purchased TDS meters, and we’ve been conducting rudimentary experiments.  Since TDS is an aggregate measure of any number of substances, we hypothesize that there could be waters with similar levels of total dissolved solids but different individual “mineral profiles,” which might taste differently.

This points to hardness.  Hardness is essentially a measure of calcium and magnesium.  So it’s safe to say waters with the same TDS and different hardness have a different “mineral profile.”  But I haven’t seen anything that says that hardness influences taste, only that it can ruin your machines.  Rao writes, “Hard water does not decrease the potential quality of coffee or espresso; even if the water feeding the coffee machines is very hard, the actual brewing water will not be too hard because much of the hardness precipitates as scale at typical brewing temperatures.”

Acids contain larger concentrations of these hydronium ions, which make them good for back massages.

Michael Mascha identifies pH as the only significant chemical parameter that influences taste, after TDS. (And carbonation, duh.)  When my feeble brain tries to put this all together, what stands out is ions.  Bear with me: pH has something to do with the activity of available hydrogen ions–that’s what the H stands for.  A hydrogen ion is a single proton without its accompanying electron, which is to say it has a positive electrical charge.  So something with low pH–an acid–has a high amount of this positive charge going on.  According to different definitions, an acid is a proton donor, or conversely, an electron acceptor.

There are other molecules with positive charges; collectively, they’re called cations.  (Molecules with negative charges are anions.)  As it turns out, water hardness is defined as the concentration of multivalent cations–molecules with a positive charge of more than one.  Calcium and magnesium, both with charges of +2, are the most prevalent multivalent cations in mineral water.  Hardness doesn’t measure cations with a charge of +1 like potassium or sodium, both of which are also common in mineral water.  Things like iron, aluminum, and mercury also qualify as multivalent cations, but if they were present in any significant amount in your drinking water they’d be toxic.  Hard water makes soap create scum instead of lather, makes water scale, and can lead to metal corrosion.

All this makes me think that:

  • hardness is a specific measure of minerality (TDS) for limited, “industrial” purposes, and
  • pH–as something like a measure of “net ionic charge”–is the best descriptor of “mineral profile,” which is to say
  • pH as “mineral profile” combined with TDS as “amount of minerality” may provide a complete description of a water’s taste.

Does this mean when I taste two waters, otherwise equal except one with x concentration of sodium ions (+1) and another with an equal concentration of bicarbonate ions (-1), the difference I taste is the “net ionic charge,” and not “the unique taste of sodium” or “the unique taste of bicarbonate”?  It starts to sound far-fetched.  Looks like we need to buy some pH testers too.  And meet some aquarium people.

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