Smooth and sweet versus floral and acidic: Any coffee aficionado can note the distinctive taste profiles that distinguish cold brew coffee from a hot cup of conventionally-brewed java.
Both beverages arise from the same starting materials, coffee grounds and water, but differ wildly in taste.
How a coffee bean is roasted and ground makes a huge difference in how the final drink tastes, smells, and feels in your mouth. But the way it's brewed is probably the most important contribution you can make to that final, sweet, sweet taste of joe.
Personally, the Tech Insider science team prefers the taste of cold brewed coffee. While we aren't going to turn our noses up to a cup of hot coffee on a cold day, we think it's fair to say that all things being equal, cold brew, subjectively, tastes better to us. Here's why.
The basics
Coffee grounds are chock full of various oils, chemical compounds, and acids. These compounds, referred to collectively as "solubles," give coffee its flavor. They're extracted from the grounds in the brewing process.
There are two basic brewing methods — which differ in brewing temperature and time — that can really change how your coffee tastes:
1) Hot-brewed drip coffee — This 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 and letting it drip through a filter and straight into a cup. This is the stuff they serve at diners. Baristas generally make hot coffee quickly, on the order of minutes, and it has a strong aroma with a sour or acidic bite.
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 "tea" from the sludgey solids. Cold brew is taking the world by storm because it 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
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 195 to 205 Fahrenheit, 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 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 sit for longer 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.
While cold brew may be more palatable to some, it 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 when compared with hot coffee.
Because cold brew takes much more time and more coffee grounds to make, it's often more expensive to buy than drip coffee. But it's actually very easy to make yourself, and it will save you a ton of money since even small cups of cold brew can set you back about $4.
Next time you're brewing a hot or cold cup of java, remember the chemistry. Your taste buds will thank you later.
