This article offers an in-depth exploration of coffee, covering a range of topics from the differences between Arabica and Robusta coffee bean species to the precise parameters of extraction time. It includes essential tips on coffee storage, a comprehensive understanding of caffeine content, and the effects of acidity and pH values on coffee extraction.
Numerous research studies suggest that coffee consumption may be inversely related to the prevalence of chronic illnesses, including cancer, cardiovascular diseases, obesity, and diabetes, and is linked to decreased mortality in both men and women. Let’s dive deeper into the art of coffee brewing.
Species of Coffee Beans
The two key ingredients for a good cup of coffee are ground, roasted coffee beans, and water. Thus, understanding the differences between the two main coffee bean species, Arabica and Robusta, is important. Generally, Arabica is the preferred choice for premium coffee due to its more subtle and aromatic taste, compared to Robusta’s stronger, but less appealing taste qualities, such as bitterness from its higher caffeine levels, and reduced sweetness.
The Arabica species accounts for 64% of worldwide coffee production. It contains approximately half the caffeine of Robusta beans and requires slightly cooler temperatures and humidity for proper growth. Arabica plants are typically cultivated between 1,000m and 2,000m above sea level. They have deeper roots and lower genetic variability compared to Robusta, due to their self-pollinating nature, while Robusta is subject to natural interbreeding within and between populations. However, Robusta is cheaper to produce.
The Impact of Roasting Degree on Coffee Quality
Roasting coffee beans is a crucial process in coffee production, responsible for developing the unique flavors and aromas that make coffee enjoyable. Roasting influences the chemical compounds and thus changes the taste, color, and aroma of coffee. Roasting also affects the antioxidant capacity and anti-inflammatory effects of coffee, in particular the antioxidant capacity decreases with higher roasting degrees.
Darker roasts or extended roasting periods are linked to a rise in bitterness and a reduction in acidity, fruitiness, and sweetness.
According to recent research, coffee roasted at 230°C for 10 minutes with a particle size of 4–6 mm showed the highest sensory acceptability score. Optimal outcomes were achieved when the roasting duration varied between 14 and 27 minutes and the temperature was maintained between 221 and 223°C. Within these roasting parameters, the overall acceptability, aroma, and flavor ratings ranged from ‘like’ to ‘moderately like’. The color spectrum spanned from light brown to brown, the taste varied from slightly to moderately bitter, and the body ranged from slightly thin to slightly heavy.
Typical Extraction Parameters for Specialty Coffee
The quality of coffee also depends on parameters during the extraction process, such as water pressure, amount of coffee, temperature, and extraction time. A widely recommended method for brewing espresso coffee involves infusing 6g of finely ground and tamped coffee in a portafilter with hot water, typically at a temperature of around 90°C, using a pressure of approximately 9 bar. It was found that 92 °C seems to be an optimal water temperature. The standard extraction time for a single espresso shot, yielding about ~25 mL, is around 25-30 seconds.
The caffeine content of 500ml dose is on average 188mg, while decaffeinated coffee contains less than 17.7mg.
After opening a package of coffee beans it is important to store them properly. In particular because exposure to oxgyen reduces the aroma and makes the taste more bitter. The best way to store coffee beans is by using a screw cap packing.
The Effect of Grinding Grades
When coffee is ground to a finer level, it increases the surface area of the particles that come into contact with water. This enhancement in surface area facilitates a more efficient extraction of key compounds like trigonelline, caffeine, and 5-caffeoylquinic acid (5-CQA) from the coffee grounds, leading to a higher yield of these substances in your brew.
Trigonelline is a bitter alkaloid found in coffee that contributes to both the aroma and the flavor, particularly during the roasting process where it breaks down to form various volatile compounds. On the other hand, 5-caffeoylquinic acid, also known as chlorogenic acid, is a significant antioxidant found in coffee. It plays a role in the taste and health benefits but can degrade when exposed to high temperatures, influencing both the flavor and the acidity. Thus, it is well established that lightly roasted coffee has higher concentrations of CGAs over dark roasted coffee.
The effect of different grinding grades changes the amount of pH, caffeine, and acidity during different extraction times. The normal coffee extraction is around 25 seconds for one cup, and the pH value increases significantly when one uses less fine-grained coffee. In addition, the amount of caffeine is higher in fine-grained coffee versus the less fine-grained ones. A similar effect is observable with the acidity, which increases in less fine-grained coffee as well.
