Cold Brew Chemistry
How a coffee bean is roasted, ground and brewed makes a huge difference in how the final drink tastes, smells, and feels in your mouth. However, the brew method – Hot or Cold is probably the most important contribution a coffee drinker can make to that final, sweet, sweet taste of coffee.
Depending on personal preferences, coffee can be brewed hot or cold with temperature and time being the main variables —:
|Roast||Medium – Dark||Light – Medium|
|Grind||Fine (depends on extraction)||Coarse|
|Temperature||92-96 degrees||Room temperature or cold water|
|Time||25-30 sec or 4min||12-48 hours|
|Method||Moka pot, French press, Aeropress, Vietnamese coffee filter, and Chemex||Steeping or Dripping|
|Description||This is what we typically imagine when we think of hot coffee. Here you are either percolating home coffee pots or by drizzling hot water over coffee grounds and letting it drip through a filter and straight into a cup.||Either steeping or dripping water through coffee grounds.|
Steeping Method – In a jar, French press, or Toddy system 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 liquid coffee from the sludgy solids
Dripping method –Water is slowly dripped through filtered water through coffee. The resulting coffee is naturally filtered through the coffee grounds and filter paper.
Cold brew is popular as 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.
What’s left in both methods is a black coffee concentrate that is thinned with water or milk before it is served.
Coffee grounds have lots of different oils, chemical compounds, and acids referred to as “solubles”. When you mix coffee grounds with water, chemical reactions take place that pull soluble from the grounds, giving you a liquid we all call “coffee”.
Coffee is technically a solution of coffee solubles and water.
- Over 1500 chemicals
- 800-100 aroma compounds
Given that coffee grounds are used in both hot and cold brew methods, the principle variables are grind type, temperature and time.
Coffee solubles dissolve best between 90 to 96 Degrees, so coffee brewed with hot water has a more full-bodied, flavourful taste profile than cold brew.
Hot water 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.
With more coffee solubles extracted, hot brew coffees are described as more full-bodied and flavourful when compared to cold brew. Moreover, due to increased volatility with higher temperatures, the aromatics are more readily released from coffee, giving rise to that beloved scent of freshly-brewed coffee.
But 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.
Oxidation and degradation also occur more rapidly at higher temperatures.
The oils in coffee solubles can oxidize more quickly at elevated temperatures, causing coffee to taste sour. Acids also degrade, the most notable of which is chlorogenic acid into quinic and caffeic acid, causing coffee to taste bitter
Cold Brew Coffee
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 flavourful oily, acidic solubles, it has to sit for longer to create a strong brew. You also have to 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.
It may not smell as fragrant as drip coffee, since cold and room temperature liquid doesn’t volatize the aromatic compounds.
To note, brew time does not determine caffeine content, nor does bitterness indicate coffee strength.
Coffee “strength” is defined as the amount of dissolved coffee solubles per unit of coffee volume. Given this, cold brew produces stronger coffee, given that the brewing process purposely concentrates the coffee solubles.
Because cold brew takes much more time and more coffee grounds to make, it’s often more expensive to buy than drip coffee.
Cold brews would definitely contain a higher caffeine content, since it uses a higher coffee grounds to water ratio compared to hot brews.
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Brewing—How to Get the Most Out of Your Coffee. Mountain City Coffee Roasters.
Sunarharum W, Williams D, Smyth H. Complexity of coffee flavor: A compositional and sensory perspective. Food Research International. March 2014; 62: 315-325.
Giuliano, Peter. “Why you should stop cold-brewing, and use the Japanese Iced Coffee Method.” Dymaxion.
What Everyone Ought to Know About Iced Coffee & Cold Brew. (2012, June 26). Prima Coffee.