By SCOTT MANLEY of La Marzocco for the Coffee Technicians Guild (CTG) blog. The CTG is an official trade guild of the SCA dedicated to supporting the coffee industry through the development of professional technicians. Learn more about the CTG here.
I took chemistry in high school and I have a certificate in Horticulture from a community college (which I vaguely recall involved some chemistry), but neither of those qualifies me in the slightest to expound on the subject of general chemistry. However, I did work in the water filtration industry for 5 years and my understanding of water and water treatment is solely related in application to municipal drinking water to the specialty coffee industry. Before that, I gained enormous experience managing equipment for Starbucks in several markets with challenging water.
As you can imagine, the subject of water chemistry came up once or twice, somehow I managed to get through it. I say this, because most of us are probably not chemists either, but as technicians we have had to use some chemistry vocabulary to communicate with a customer or colleague about a water equipment issue. So, I’m betting you share my pain.
You may have heard that seventy percent of service calls on coffee equipment are water-related. Communicating the details of a water-caused equipment failure or issue to customers or colleagues can range from entertaining, challenging, or downright frustrating. For example, I had a customer who removed their Reverse Osmosis (RO) system from their cafe to save on the cost of maintaining it. Reasons given were that it needed filter changes every quarter, someone had to verify that it was working, and when it stopped working there was no water to the equipment. Incidentally, I was not responsible for maintaining it, that was someone else’s job (an HVAC company actually), and they were not great about communicating the work they did and so the RO was problematic for the customer, and hence removed. If you are familiar with the effects of hard water, you may know where this story is going.
The long and the short of it is that the customer ended up spending an additional $4,000 in equipment maintenance costs on their brewing equipment over the course of one year. And yes, I did inform the manager on every service call (about one per month) that this was the result of the RO system being removed. I tried six ways from Sunday to convince them to install proper treatment. I told them all about how hardness ions precipitate out of water under heat and pressure. And it still took over a year to get them to a place where they understood they needed to do something. Probably because every time I spoke with them, I had to start from the beginning, as they had no vocabulary about water. This wasn’t a specialty coffee or third wave cafe either, so their level of interest was solely related to how much it was going to cost.
Fortunately, we have a frame of reference to start from in the specialty coffee industry. Our parent organization, the SCA, has a basic water standard that has some fairly well-defined metrics that we can use to define our water. Here is a summation of those water parameters from a presentation at last year’s Specialty Coffee Expo in Seattle, WA.
T.D.S. stands for Total Dissolved Solids and is a measure of all dissolved solid substances contained in water. A TDS meter is used to measure the concentration of dissolved solids. This value is expressed in units of parts-per-million or ppm. Note: A test measuring the electrical conductivity of the water provides only an estimate of the TDS present, as conductivity is not precisely proportional to the weight of an ion and nonconductive substances cannot be measured by electrical tests.
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. Hardness can be measured using dip strips or a titration kit. This value is expressed in ppm (it may also see it expressed as grains-per-gallon; one grain is approximately 17 ppm).
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. Test using a dip strip or titration kit.
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. Free chlorine is tested with a dip strip or a titration kit.
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. Total chlorine is tested with a dip strip or titration kit. Due to the volatility of chlorine, testing should be performed as close to the sample collection as possible.
pH stands for potential of hydrogen and is a numeric scale used to specify the acidity or basicity of water. Water with a pH less than 7 is acidic and water with a pH greater than 7 is basic (alkaline). 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 temperature tells how hot something is but not how much heat the substance carries. 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. pH is measured using test trips or pH meter.
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. Alkalinity is measured using a dip strip or titration kit.
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. Chloride is measured using a dip strip or titration kit.
Now, having put the above out there, I have heard those parameters explained differently, maybe even more clearly. And you may have heard these explained with more or less specificity. The point is to have a starting place, and I invite all of you to the conversation, be it through email, phone, the Coffee Technicians Guild Slack channel, or in person.
Our next article is about water testing and maintenance strategy, where we will take the above parameters and apply them.
Take care all. See you next month in Seattle!
The Coffee Technicians Guild is an official trade guild of the SCA dedicated to supporting the coffee industry through the development of professional technicians. The CTG strives to be the voice of technicians within the coffee community. Learn more about the CTG here.