by Andrew Timko – roaster and green buyer
Water is the sole carrier used to dissolve the sheer abundant and varied solute, coffee. Water is 98.8 – 98.2 % of the beverage we call drip coffee. 30% of the weight of dry coffee grounds is made up of components that can be dissolved, or are soluble. Of that 30% only 18-22% is desired as a result of the extraction process either for espresso or drip coffee, regardless of strength. The 18-22% of the soluble components of dry coffee grounds represents only 1.2 – 1.6% of the beverage called drip coffee. With water comprising 98.8-98.2% of the beverage it quickly becomes obvious it’s importance in the coffee brewing process. There are many considerations to take into account before discerning and establishing your water quality program. In this blog I will discuss, in a very non-scientific manner, the influences that affect water quality, this will be followed with two additional blogs expanding on the water’s role in coffee. The second will be on water composition affect on taste; and the third will be on choosing filtration and customizing water.
First, the source of your water has a distinct influence on the quality of the water. Surface or Ground water are the primary source of municipal water. Surface water comes from a lake, river or other “surface” sources. St. Louis City is a surface water town; our water is collected from the Mississippi and Missouri Rivers and treated for our tap water. Surface water is primarily rain collecting and traveling over streets, in rainwater collection drains, congregating into streams, lakes or rivers. That runoff collects an untold number of pollutants: industrial discharge; pesticides; agricultural deposits (animal waste) herbicide runoff and fertilizer that can influence the water arriving at our tap. And these various pollutants vary constantly making it impossible, without constant analysis, to determine how the water is being influenced by these pollutants. The municipal water division takes it upon itself to remove and sterilize this water to make it safe for drinking. Here is a link to St. Louis Water divisions’ water tests: http://www.stlwater.com/confidence.php what is immediately apparent are the number of “extras” in the water that occur at low but traceable levels in our drinking water. This is normal and is well below the levels recommended by the USDA. The St. Louis Water Division does and amazing job of treating our water to make it safe for drinking, just not for brewing Specialty Coffee. So let’s discuss some of the variable used to evaluate water for brewing coffee.
The source of the water can assist in understanding the general composition of the water. For water to highlight the soluble components of coffee we will need to discuss the basic components that affect extraction. Total Dissolved Solids (TDS) is a measure of the combined organic and inorganic components absorbed in the water. This is only a starting point. TDS is a range that gives you a picture of all the material contained in the water without differentiation. For drinking water to be considered “safe” by the USDA it needs to be less than 1000mg/L TDS. St. Louis allows a maximum of 500 mg/L and according to the 2012 Consumer Confidence Report runs an anywhere between 241-434 TDS. The ideal target recommended by the Specialty Coffee Association of America (SCAA) for coffee brewing is 150 mg/L TDS and the SCAA range is 75-250mg/l. When TDS of water is higher than 250mg/L the “space” available on the water molecule becomes limited, prohibiting sufficient absorption of soluble solids and contributing unwanted taste to the water. When TDS of water is below 75mg/L or at zero like Distilled water there is too much available space for extraction of the soluble solids. Not all soluble solids are desirable and when the TDS is too low and over-extraction occurs quickly. TDS is just the starting point. There are 600 volatile aromatic compounds in coffee and each one of them can be affected differently during and after extraction. Coffee is a constantly moving target and every flavor and aromatic compound is effected by and influenced by the composition of the water.
Our next consideration is hardness. Hardness is the amount of Calcium and Magnesium and in some cases iron, aluminum and manganese present in the water. Water tends to be slightly acidic just as a result of the absorption of carbon dioxide in the atmosphere. As this water penetrates the earth the water collects minerals to balance the slightly acidic rainwater. Well water or aquifer water generally has a higher measured hardness and needs some type of softening to prevent accelerated scale build up in equipment. Hard water also tends to be basic or alkaline as a result of the mineralization that occurs en route to the aquifer or well. Water that has very high measured hardness is usually the result of over mineralization due to acid rain. The carbon dioxide absorptions, mentioned earlier, lower the PH of the water making it slightly acidic, but additional pollution can lower the acidity of the water even more. And this can result is very high measured hardness in ground sources. In St. Louis the Total hardness on average is 144 mg/L and has can run from 94-229 mg/L of hardness. For Calcium SCAA recommends a target hardness of 68mg/L. In St. Louis the Calcium hardness can be anywhere from 18-28 mg/L. This is lower than the recommended target but is in the range of acceptable Calcium hardness.
The final water quality consideration is chlorine. Chlorine is used in municipal water treatment to destroy harmful pathogens that reside in the water system, and is a necessary part of healthy drinking water. But chlorine also destroys beneficial aromatics and oils by accelerating oxidation. The SCAA recommends zero presence of chlorine in water for coffee. Chlorine can easily be removed by heating the water or by using carbon filtration, but St. Louis uses Chloramines. Chloramines are much harder to remove from water through carbon filtration or heating, since it is not a free-chlorine. This leaves us with the question of how these variables affect water qualities and how it is addressed. I will explore that in my next blog post when I discuss how water quality affects the taste of coffee, then follow that up with a blog on filtration options.