The formula for an Espresso “perfetto” starts with the water you use: temperature and quality of water are fundamental. Water comprises 98% of the average cup of coffee, so it’s not a stretch to think that water quality significantly impacts the final result.
Local tap water contains certain levels of calcium and magnesium, so water quality, or the liquid’s “hardness”, refers to its mineral level, which influences how the hot water and coffee interact; water that’s too hard or too soft can negatively impact the final cup. Many experts, including Andrej Godina, Coffee Expert and Authorized Trainer at the Specialty Coffee Association, suggest measuring water hardness and if necessary, inserting water softener. If using bottled water, opt for one with a fixed residue of about 200-300 mg/L. The ideal brewing water is not too sweet with balanced minerals that enhance the coffee’s natural flavours without overwhelming them.
In addition to the right hardness, the water temperature must remain stable throughout brewing since how the water penetrates the coffee dose is key to a perfectly balanced extraction. The perfect brewing temperature is between 83° and 92° Celsius. However, coffee connoisseurs believe keeping to the lower end of the scale releases the coffee’s more complex flavours.
Once the coffee and water are in place, pre-infusion and extraction occur. Pre-infusion involves ground coffee soaking gently in the filter before applying brewing pressure in order to ensure that water penetrates the grounds evenly once the extraction begins.
Extraction happens when pressurised hot water percolates through a layer of roasted, ground and compacted coffee and flows out from the filter spouts, extracting the characteristics of the coffee into the cup. It determines both the quality of the cup and the thickness of the crema, affecting the liquid’s fine, persistent texture.
Under-extraction occurs when the water flows too quickly, failing to capture the coffee grains’ substances. Yet, under-extraction isn’t tied solely to water flow; it can also be caused by old coffee, under-heated water, insufficient coffee grain dosage, or weak compacting. Under-extracted coffee is less full-bodied than the classic Espresso–the crema dissolves, the aromatics are weak, and the flavours are bland. Alternatively, overpacking the filter, too fine grinding and/or excessive compounding could lead to over-extraction. It results in a dark, exceptionally bitter liquid that emits an unpleasant aroma with a crema that tends to split in the centre and cling to the edge of the cup.