By Scott Manley, La Marzocco
Mercuric Thiocyanate is my new favorite word. I’m adding it to my personal water vocabulary of seemingly difficult to pronounce terms along with Hexavalent Chromium and Trihalomethanes.
Hexavalent Chromium and Trihalomethanes, in case you are unfamiliar, are not something we are concerned with when testing water for coffee, as they are not associated with either equipment failure or extraction issues. They are, however, commonly tested for analytes in water. I occasionally reference them when speaking to other water quality professionals about water testing and the specific needs of specialty coffee. For me they serve as a frame of reference for the particulars of water that we are most concerned with. They are at the other end of the spectrum of contaminants, the dangerous ones, that most EPA accredited labs test for. And most presorted tests will include these within a standard range of tests. Thankfully, the vast majority of our drinking water is biologically safe to drink and brew with. So we get to focus on testing for the components that do affect equipment and brewing.
According to Wikipedia (n.d): Mercury(II) thiocyanate (Hg(SCN)2) is an inorganic chemical compound, the coordination complex of Hg2+ and the thiocyanate anion. It is a white powder.
I received a bottle of the stuff via Amazon Prime last week.
Mercuric Thiocyanate has two major commercial uses; first, it can improve detection limits in the determination of chloride ions in water by UV-visible spectroscopy (I am currently setting up the processes to use a spectrophotometer for water analysis). And second, it was used in pyrotechnics, when the compound is in the presence of a strong enough heat source, a rapid exothermic reaction is started which produces a large mass of coiling serpent-like solid, also called Pharaoh's serpent or Pharaoh's snake you can see it in action here. I remember these from my childhood. Oh, and also it's toxic.
Testing for the analyte chloride, using it’s associated toxic reagent, Mercuric Thiocyanate, makes using a spectrophotometer less than practical in the field. They are also expensive, require frequent calibration, and don’t easily fit in a tool bag. So, when one is on a field service call for equipment repair there are other more efficient and economical ways to get a snapshot of the water quality while onsite. I have previously written about the TDS meter, the most common tool used, and its relative usefulness and limitations. Every tech should have one and know how to use it. It is practical, inexpensive and provides a quick hit on one measurement of water quality. In my last position as master technician and technical trainer at Ecowater Systems, techs were required to record TDS and general hardness measurements on every espresso service work order to ensure, at a minimum, that we were not ignoring potential water issues that our customer should be informed of.
Another set of tools I believe is import to have on hand are test trips, also called dip strips. While not as accurate as a lab test, they are far more accessible and easy to carry in a tool bag. You also get the results right away, which is important when reporting to a customer about a water related issue or equipment repair while onsite. When used properly, they also can provide the tech with confidence needed in communicating with operators and managers who ultimately are charged with making decisions about the timing and expense of treating water in the cafes we service. Test strips consist of a ribbon made of plastic or paper of about 5 millimeters wide, plastic strips have pads impregnated with chemicals that react with the compounds present in water. For paper strips the reactants are absorbed directly onto the paper. Paper strips are often specific to a single reaction (e.g. pH measurement), while the strips with pads allow several determinations simultaneously. The resultant chemical reaction of the reagent in the water sample is indicated by a change in color on the test strip. Test strips are packaged either as a set with a range of tests or individually in foil packets for specific analytes. They are one time use tools that do not require batteries, special handling or calibration.
The instructions for using them are not uniform, but are specific to each test with regards to the parameter being tested, so it is important to read the instructions carefully before using them. Most of the reported errors or discrepancies with test strips are due to users not familiarizing themselves with these procedures beforehand. So if you are unfamiliar with, or using a test for the first time, slow down, read the instructions, and be deliberate. The more you use them the easier it gets, and the more confidence you have in the results.
There are test strips for nearly all of the parameters of water quality that we in the specialty coffee industry are concerned with. Most test strips cost less than a dollar each, which makes them relatively inexpensive to incorporate into your service call. To put this into perspective, I have been surveying costs of EPA and state accredited labs for water analysis, with the cost being between $85 and $160. There is also some variability with regards to shipping costs for samples which can add even more cost. The average turnaround time for getting results seems to fall right around 2 weeks; or about the time it takes for an operator to completely forget that a water issue is the underlying cause of their recent service call (and potential future service calls).
The primary test trips most techs would be using are those that test for same parameters identified by the SCA and equipment manufacturers for proper brewing and equipment longevity. They are:
- Total Hardness - the amounts of divalent metallic cations, principally calcium hardness and magnesium hardness, expressed in terms of calcium carbonate equivalent. Or the sum of the concentrations of Calcium (Ca2) and Magnesium (Mg2) in water.
- Total Iron - a common element often present in groundwater, iron may be found in soluble form such as in ferrous bicarbonate, bound with a soluble organic compound, and as suspended ferric iron particles. Iron above 0.3 mg/L is objectionable in water because of staining of laundry and plumbing fixtures caused by the oxidation and precipitation of ferric hydroxide and/or ferric oxide (ferric iron) into small solid iron particles. Iron can also give a metallic or distorted flavor to beverages.
- Free Chlorine - a disinfectant added to water. It is the portion of the total available residual chlorine composed of dissolved chlorine gas (Cl2), hypochlorous acid (HOCl), and/or hypochlorite ion (OCl-) remaining in water after chlorination. This does not include chlorine that has combined with ammonia, nitrogen, or other compounds.
- Total Chlorine - the sum of free chlorine and combined chlorine. Combined chlorine is also a disinfectant, known as chloramines, and is free chlorine in the presence of ammonia or organic nitrogen in water. The combined chlorine compounds are more stable than free chlorine forms, but are somewhat slower in reactions. This is the important distinction from free chlorine as it is more difficult to remove via activated carbon, requiring about 4 times the contact time of free chlorine.
- pH – a measure of the degree of the acidity or the alkalinity of a solution as measured on a scale ("pH scale") of 0 to 14.The midpoint of 7.0 on the pH scale represents neutrality--that is, a "neutral" solution is neither acid nor alkaline. Numbers below 7.0 indicate acidity; numbers above 7.0 indicate alkalinity.
- It is important to understand that pH is a measure of intensity, not of capacity. That is, pH indicates the intensity of alkalinity or acidity in the same way current measures the intensity of the voltage in a circuit, but not how much voltage is present.
- More specifically, pH is the negative of the logarithm of the hydrogen ion concentration of a solution. The neutral point of 7.0 actually indicates the presence of equal concentrations of free hydrogen and hydroxide ions.
- Alkalinity - is the capacity of water to resist changes in pH that would make water more acidic. The quantitative capacity of water to neutralize an acid; that is, the measure of how much acid can be added to a liquid without causing a significant change in pH.
- Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have high alkalinity.
- Chloride - is an anionic compound containing chlorine and another element such as sodium, calcium or magnesium. Chloride content has been correlated to corrosion of stainless steel and boiler failures.
I gave a presentation earlier this year during the Specialty Coffee Expo demonstrating field testing using dip strips and was made aware of one significant drawback to using colorimetric testing, which includes drip strips and manual titration; and that was when one of the attendees announced he was colorblind. I was previously unaware that 8% of men are colorblind in various degrees, with red-green being the most common. If you are colorblind there are ways to work around this, one is to acquire a handheld photometer which will translate the reagent color to a numerical value, another possible solution is to see a vision specialist about color-correcting glasses.
I would encourage everyone to investigate adding dip strips to your parts stock and service regimen. Having the right tools to identify water problems and documenting your work will help you to have confidence in communicating with customers and industry partners. Assessing water quality before it becomes a problem is just another way to look out for your customers, because the right water not only helps the equipment run properly, but it also makes the coffee taste right, and that’s what we’re all here for.