What is cold brew coffee?

Cold brew is coffee made by steeping coarsely ground beans in room-temperature or chilled water for 12 to 24 hours, then filtering. Cold extraction produces a naturally sweet, low-acid and very low-bitter cup because the acidic and bitter compounds stay largely insoluble in cold water.

Contrary to a common belief, cold brew is not a recent invention of the New York specialty scene. The oldest documented trace is Japanese, under the name 'Kyoto-style cold brew' or 'Dutch coffee', a slow cold drip method dating to the 17th century — Dutch merchants in Nagasaki likely introduced the technique to Dutch sailors. The modern immersion version took hold in American cafés around 2010-2012 and went global via chains like Stumptown.

The chemistry explains the cup profile. Cold extraction is dramatically slower than hot: it takes 12 to 24 hours at 4-20 °C to reach an extraction comparable to 4 minutes of French press at 93 °C. But the slowness is selective: chlorogenic acids (responsible for acidity and, when degraded, bitterness) are less soluble in cold water. A cold brew typically carries 60-70 % of the titratable acidity of a regular filter coffee. It is often easier on sensitive stomachs.

Caffeine content in cold brew is not intrinsically higher than hot — it is all about ratio. Cold brew recipes use more concentrated ratios (1:4 to 1:8 for a concentrate to dilute, 1:15 to 1:17 for ready-to-drink) because the liquid often serves as a base, cut afterward with water, ice or milk. A 1:4 concentrate can hit 200-300 mg of caffeine per 100 ml, two to three times a regular filter by volume — but it gets diluted.

In Belgium, cold brew appeared in specialty bars around 2014-2015, first in Brussels (Saint-Gilles, Ixelles) and then Ghent and Antwerp. It is especially popular from May to September iced, sometimes with maple syrup or cane sugar, or topped with oat milk for a cold brew latte. Nitro cold brew — cold brew infused with nitrogen for a Guinness-like creamy texture — landed in Belgium around 2017-2018.

Cold brew vs iced coffee vs Japanese iced

Time as a Brewing Variable

Cold brew coffee is one of the most striking demonstrations of how fundamentally temperature affects extraction chemistry. In hot brewing, the heat provides the energy needed to dissolve a wide range of chemical compounds from the coffee grounds quickly and efficiently — acids, bitter alkaloids, melanoidins, aromatic esters, and sugars all dissolve in minutes at 90-95 °C. In cold brewing, the absence of heat means only the most soluble compounds — primarily larger sugars and mild acids — dissolve in the cold water over an extended period, while the heat-sensitive aromatic compounds that define the volatile character of a hot-brewed specialty coffee are never generated and the harsh bitter compounds that require elevated temperature for dissolution remain in the grounds. The result is a chemically simpler beverage that is sweeter, lower in bitterness, and naturally lower in perceived acidity than its hot-brewed equivalent.

The concentrated format of most cold brew recipes (1:4 to 1:7 coffee to water, producing a concentrate for dilution) is practical rather than driven by any quality consideration — it allows more efficient use of the refrigerator space during the steep and produces a shelf-stable concentrate that can be diluted on demand over several weeks. The diluted final drink (typically 1:1 concentrate to water or milk) reaches approximately the same strength as a standard hot-brewed cup. Cold brew retains good freshness refrigerated for up to two weeks, far longer than hot-brewed coffee, making it a practical option for batch preparation in café or home contexts where daily brewing is inconvenient.

Practical Recommendations

For home cold brew, the most accessible method is the jar-and-strainer approach: 100g of coarsely ground coffee in a 1-litre jar with 600g of cold filtered water, stirred to saturate all grounds, covered and left at room temperature for 12-16 hours, then strained through cheesecloth or a paper filter into a clean jar. Refrigerate the strained concentrate immediately. The resulting concentrate will keep well for up to 14 days refrigerated. Dilute 1:1 with water or milk over ice for serving. For a smoother, cleaner concentrate, use the refrigerator steep method (longer time, 18-24 hours at 4 °C) which produces a less aromatic but more stable concentrate with less risk of over-fermentation in warm weather. Medium and dark roasts produce the most satisfying cold brew; very light roasts can produce a concentrate that is sharp rather than sweet due to the acid compounds that cold water does extract effectively.