Chemistry behind Coffee Brewing
Although the way in roasting coffee beans and the ground makes a huge difference in the final drink tastes, smells, and feels in our mouth. The way in brewing is of paramount importance to the final sweet taste.
The Basic Principle
Coffee grounds are completely full of various oils, chemical compounds and acids. These compounds, being referred to as “solubles” collectively, give coffee its flavor. In the brewing process they are extracted from the grounds.
There are two basic brewing methods, both differ in brewing temperature and time which can really alters the coffee tastes:
1) Hot-brewed drip coffee is what we typically imagine when we think of hot coffee. Most people make it in percolating home coffee pots or by drizzling hot water over coffee grounds through a filter and straight into a cup. Baristas make hot coffee quickly and it has a strong aroma with a sour or acidic taste.
2) Cold brew – Baristas make cold brew by soaking coffee grounds in room-temperature or cold water and then let it sit and steep like tea for hours or even days. Then they strain the resulting coffee from the sludgy solids. Cold brew often has a deeper, less acidic and more subtle taste, and is more concentrated than conventionally-brewed coffee. It’s also a refreshing way to get your caffeine fix on a hot day.
The chemistry behind coffee brewing
When mixing coffee grounds with water, chemical reactions start, pulling solubles from the grounds and giving the resulting liquid its quintessential coffee taste and smell.
Coffee solubles dissolve best between 195 to 205 deg F (91 to 96 deg C), therefore coffee brewed with hot water provides a more full-bodied, flavorful taste profile than cold brew. Hot water also pulls the soluble chemicals from the grounds rapidly, making them more volatile. As a result they evaporate into the air more easily and waft into our nose, giving off sweet-smelling aroma.
However increased solubility isn’t always good. Boiling water causes coffee’s chemical compounds to degrade and oxidise, giving the coffee a sour and bitter taste.
Oxidation and degradation also happen in brewing coffee cold, but it happens at slow pace. This is why cold brew almost never tastes acidic or bitter. It also stays fresh longer than hot-brewed coffee, lasting 2 to 4 weeks refrigerated. Hot coffee usually goes stale after a day.
But, since the water temperature of cold brew is below the optimal temperature to drag out those flavorful oily, acidic solubles, it has to taking longer time to create a strong brew. Baristas also add about twice as many grounds to cold brew as they do to conventional brew, which helps to boost the concentration of solubles in the final product.
Cold brew doesn’t smell as fragrant as drip coffee, since cold and room temperature liquid doesn’t volatilize the aromatic compounds. This gives cold brew a duller smell compared to hot coffee.
Because cold brew takes much longer time and more coffee grounds to make, it’s often more expensive than drip coffee.
Caffeine Crystals and Coffee Chemistry!