After trying my first cold drip coffee I was hooked, the cleanliness, the crisp vibrate flavour. I had to understand more why this was so different to the espresso coffee I had been making for years. Here's what I found.
I also built a tower to create this delicious drink. See right side. With cold extraction around 6 hours, we’re able to bring out the more subtle flavour characteristics. When you mix coffee grounds with water, chemical reactions take place that pull solubles from the grounds, giving the resulting liquid its quintessential "coffee" taste and smell. Coffee solubles dissolve best between 90 to 96 degrees, and around 9 bars of pressure so coffee brewed with hot water has a more full-bodied, flavorful taste profile than cold brew. Hot water also pulls the soluble chemicals out of the grounds quickly, and makes them more volatile*. This means that they evaporate into the air more easily and waft into your nose, giving off that sweet-smelling aroma. But increased solubility** isn't always a good thing. Boiling water causes coffee's chemical compounds to degrade and oxidize — kind of like how iron becomes rusty when it's exposed to too much oxygen — giving the coffee a sour and bitter taste. If you're not a fan of this taste, this is where cold brew saves the day. Oxidation*** and degradation still happen when you brew your coffee cold, but it happens much more slowly. 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 few hours. But, since the water temperature of cold brew is below the optimal temperature to drag out those flavorful oily, acidic solubles, it has to sit for longer to create a strong brew. In context of coffee: *volatility. In contrast to solubility- the ability of materials to dissolve- volatility is the ability of substances to turn into vapor, and be transported through the air. Volatility also increases with temperature: that’s why hot coffee is so aromatic. Problem is, when you’re smelling coffee, it’s losing its aromatics to the air. Cooling the coffee quickly, though, reduces volatility dramatically. This effectively locks the ephemeral volatiles (like floral and fruit notes) into solution until the coffee is warmed again. This happens on the coffee’s way down your throat, which sends a punch of beautiful volatile aromatics through your retronasal pocket to your olfactory receptors. **Solubility is the ability of substances to dissolve, in our case, in water. Coffee has soluble constituents; that’s why we can run water through it and the water becomes a solution of coffee solubles and water, creating the beverage we call “coffee”. The thing about solubility is this: substances are generally more soluble at higher temperatures and less soluble at lower temperatures. This is why sugar dissolves very slowly in cold water but very quickly in hot water. When we brew coffee, we use hot water to dissolve the coffee solids out of the coffee grounds and into the water, and as we know this happens best at 90 to 96 degrees. You can try to use cooler water, but this means that the coffee will dissolve incompletely; many of the soluble substances in coffee won’t make it out of the grounds and into the water. This is what happens in cold brew: the technique tries to make up for the relative insolubility of coffee at cold-water temperatures by brewing for a long, long time. ***Oxidation in food is generally bad news: oxygen has a habit of monkeying with oils to make them taste horrible, a phenomenon also known as rancidification. You know that funky taste of an unclean coffee hopper or french press screen? That’s oxidized coffee oils. Coffee kept warm takes on these same flavors, since oxidation happens much more quickly at high temperatures. This is another reason why cooling coffee quickly after brewing is essential. |