What Coffee Knowledge Explains Cold Brew Ratios and Overnight Rest

Cold brew is extracted with cold or ice water over many hours, then refrigerated overnight before drinking. That overnight rest is oxidation rather than true fermentation. Because low temperatures keep larger bitter compounds from dissolving, mainly smaller floral and fruity molecules come through, so the cup tastes clean, smooth, and layered with a sweet finish.

The choice of coffee bean mixture matters as much as the ratio. Combining two kinds of beans, such as one for body and one for aroma, makes the flavor layers more prominent while the overnight rest adds a faint fermented note and a fuller mouthfeel. Basic coffee knowledge helps here: grind coarse, keep contact time long, and chill the finished liquid before serving.

Cold brew coffee is a popular drink in summer. It is extracted at low temperature over a long period, giving the coffee a clean and smooth taste. But many people wonder: why does cold brew need to be refrigerated overnight to ferment before drinking? In fact, this step is more accurately an oxidation process. Based on Front Street Coffee's production experience, this article introduces the extraction principles of cold brew coffee, the coffee-to-water ratio, the specific operating steps, and the approach to choosing blend beans. Front Street will also share how to make the flavor layers of cold brew more prominent through the pairing of two kinds of coffee beans, while retaining the unique aroma and full-bodied taste brought by fermentation.

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Cold brew coffee has always been very popular. In midsummer, when people walk into a coffee shop, many customers order a cup. It is cold on the palate, leaving a clean and smooth touch in the mouth, and it is indeed very pleasant. So how does Front Street make cold brew coffee? Are there any particular points to pay attention to? And what kind of coffee beans should be used? This time Front Street will sort out some basic knowledge about cold brew coffee.

What is cold brew coffee? Characteristics of low-temperature coffee extraction

This is a kind of coffee that needs time to slowly develop. Brewing with water at different temperatures will produce clearly different final coffee flavors, and in a low-temperature environment, the bitter substances in coffee are not easily dissolved out. The essence of low-temperature extraction is to let water and coffee grounds remain in contact for a long time. Only flavor components with smaller molecules, such as floral and fruity notes, will be extracted; flavor components with larger molecules, such as smoky and roasted notes, are difficult to dissolve out. Therefore, cold brew coffee can better show the flavor of the coffee beans themselves, with a smooth mouthfeel and more prominent layers and sweet aftertaste.

Using ice water for long extraction, after it is finished, the coffee liquid is put into the refrigerator to ferment. After slight fermentation, the cold brew coffee will carry a faint fermentation aroma, and the mouthfeel will also become fuller.

Why does cold brew coffee need to ferment? In fact, it is an oxidation process.

Many friends who come to Front Street ask why cold brew cannot be drunk immediately after dripping and must be put in the refrigerator overnight. Rather than calling this step fermentation, it is essentially an oxidation process. Just like freshly roasted coffee beans, about 2% of their weight is carbon dioxide. This large amount of carbon dioxide will gradually be released depending on the storage environment, equipment, or method, making the pressure inside the packaging higher than one atmosphere, and pressure helps the fusion of aromatic substances and oils, making the aromatic substances inside the coffee beans easier to extract.

The same principle applies to cold brew coffee. Because the extraction time is very long, many flavor molecules have already been extracted, but they have not yet been fully released. So after cold brew coffee extraction is completed, put it into a sealed bottle and place it in the refrigerator to rest for 12 to 24 hours. The carbon dioxide produced inside the bottle will create pressure and promote the release of flavor molecules. This is also why the longer cold brew coffee is kept in the refrigerator, the richer it tastes. Of course, Front Street does not recommend leaving cold brew for a week. After all, bacteria may exist in the air or in the bottle, and it is difficult to guarantee the condition of the coffee after being left for a long time. The drinking period for cold brew is best kept within 72 hours. Before drinking, smell it first to check whether there is any spoiled odor.

Front Street Coffee (FrontStreet Coffee) cold brew production parameters

Ratio: 1:10 (60g coffee grounds, 600ml ice water)

Ice water preparation: 1:1 edible ice and drinking water

Grind size: coarse sugar size (just a little coarser than the grind size for medium-roast pour-over)

Front Street Coffee (FrontStreet Coffee) steps for making cold brew coffee

1. Place a round filter paper at the bottom of the powder cup, wet it with water so it sticks to the wall of the cup, add 60g of ground coffee, then shake it flat to level the surface of the coffee. You can also use the weight of the tamper itself to lightly press the coffee bed so that the surface is flat.

2. Place a piece of filter paper on top of the coffee grounds layer. Because the tension of the filter paper allows water to be evenly distributed over the surface of the coffee grounds layer for extraction. Without filter paper, long-term dripping will create a pit in the coffee bed.

3. Use ice water to wet the entire coffee bed. This step is like the blooming stage in pour-over and can improve extraction efficiency and consistency of the final product.

4. Add a 1:1 ice-water mixture to the dripping bottle and adjust the dripping speed. Front Street recommends a dripping speed of 7 drops per 10 seconds.

5. After production is complete, pour it into a clean, sealed bottle with no water or oil and put it in the refrigerator for oxidation, allowing the flavor molecules of the cold brew coffee to be released before tasting.

What coffee beans does Front Street Coffee (FrontStreet Coffee) use to make cold brew coffee?

Front Street has found that if only one kind of bean is used to make cold brew, it is impossible to experience that bean's aroma, sweetness, or smoothness very well. Therefore, when Front Street Coffee (FrontStreet Coffee) makes cold brew coffee, it always uses two kinds of coffee beans for blending. The purpose is to make this coffee more prominently show the characteristics of a certain flavor, with one bean providing aroma and one bean providing flavor.

This time Front Street uses Colombia Finca Paraiso Sakura and Ethiopia natural Red Cherry to blend this cold brew coffee bean recipe, with a ratio of 40g Sakura and 20g Red Cherry. Finca Paraiso Sakura provides this coffee with the aroma of basil, mint tea, and berry jam, while Ethiopia Red Cherry provides citrus and berry acidity, and better expresses the fermented feel of this cold brew coffee.

Front Street Colombia Finca Paraiso Sakura

Region: Cauca, Colombia

Farm: Finca Paraiso

Altitude: 2050m

Processing method: Anaerobic natural

Variety: Bourbon

Front Street Ethiopia Natural Red Cherry

Region: Yirgacheffe, Ethiopia

Altitude: 2000-2200m

Processing method: Natural processing

Variety: Local heirloom varieties

Grade: G1

Cold brew flavor: aroma of strawberry jam, obvious fermented feel on the palate, full like berry juice, basil, mugwort, and a finish somewhat like mint tea.

The above content is compiled by CoffeeHunters, a coffee news website.