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The original meaning of cold brew coffee refers to the fact that under low-temperature conditions, small-molecule substances tending toward aroma and acidity are more easily released in cold water, so the coffee tastes light on the palate and mostly presents as sweet and sour. In addition, because it is not limited by equipment or location, cold brew can be said to be coffee that people can easily get their hands on. At home, as long as you have ingredients, a bottle, water, plus a refrigerator, you can easily achieve caffeine freedom.

Regarding the making of cold brew, someone asked FrontStreet: What is the difference between cold brews made with different ratios? What effects does the coffee-to-water ratio have on coffee?

As a typical immersion extraction, cold brew coffee is the process of extracting flavor through long-term contact between low-temperature water and coffee grounds in the same container. When other parameters remain unchanged, the larger the proportion of water, the lower the concentration of the coffee liquid will be, the weaker the coffee taste will be, and the thinner the mouthfeel will be; conversely, the smaller the proportion of water, the higher the concentration will be, the stronger the taste will be, and the thicker the mouthfeel will be.

Therefore, in order to find a balanced mouthfeel and allow the coffee to present a better flavor, we have to apply an appropriate coffee-to-water ratio.

How long should cold brew steep? How fine should the coffee grounds be ground?

We all know that the various parameters involved in any extraction method are more or less interconnected. For cold brew, the coffee-to-water ratio is not the only factor that determines the taste; we also have to look at grind size, steeping time, water quality, and, most critically, the coffee beans.

Although low-temperature extraction can reduce the appearance of bitter compounds, it is not one hundred percent effective, so if you want to pursue deliciousness, the coffee grounds used for cold brew should not be ground too fine, and even more so should not be steeped too long. For the former, we recommend keeping it within a range of about 80-85% passing through a 0.85mm standard sieve, so that it looks to the naked eye like the granular texture of white sugar; for the latter, it is best kept within 6 to 16 hours, because this ensures sufficient coffee-to-water contact time while also making it unlikely to show negative flavors due to over-extraction.

As for the choice of coffee beans, here Qianjie uses Kenya Little Tomato from the bean shelf as an experimental demonstration. It uses the K72 washed processing method, and the varieties are SL28 and SL34. Both SL28 and SL34 are varieties selected after multiple rounds of cultivation. SL28 belongs to the Bourbon genetic group and carries the bright tonality and rich acidity of the original Bourbon, while SL34 is genetically closer to Typica and has a milder acidity.

When Kenya AA is made into iced coffee, it enters the mouth with a feeling of dark berries wrapping around the palate, while carrying a full cherry tomato aroma. Drunk ice-cold, it is extremely satisfying, which is why it is the first bean many friends choose for cold brew.

How does cold brew coffee made with different coffee-to-water ratios taste?

Because cold brew is always carried out in an environment of 0-10°C, the extraction efficiency is very low; in addition, the coffee grounds and water are in a relatively static state, and there is no external force driving them along the way, so the speed at which the coffee grounds dissolve flavor substances is very limited. To make the experimental results clearer, Qianjie set up 4 relatively common coffee-to-water ratios here, namely 1:8, 1:10, 1:12, and 1:15, while all other parameters remained unchanged.

The preparation steps are entirely the same: pour the coffee grounds and water into the container in sequence, then stir and seal, then place it in the refrigerator. When the time is up, take it out and filter it (you may stir once in between).

Coffee beans: Kenya Little Tomato

Dose: 18g

Steeping time: 6 hours

Grind size: fine granulated sugar / 80% pass-through rate on China No. 20 standard sieve (EK43s setting 9.5)

Coffee-to-water ratio: 1:8, 1:10, 1:12, 1:15

Corresponding water amounts: 144g, 180g, 216g, 270g

At a coffee-to-water ratio of 1:8 the coffee liquid has the darkest color, the strongest and most sour taste, and the mouthfeel is even a bit salty, with only a hint of berry in the flavor and a bitter finish;

At a coffee-to-water ratio of 1:10 the coffee liquid smells of fresh sugarcane, with flavors of red plum, berries and snow pear tea, a slightly heavy mouthfeel, high acidity and no obvious sweetness;

The cold brew at a coffee-to-water ratio of 1:12 has the cleanest mouthfeel, with flavors of cherry tomato, red plum, smoked plum juice and sugarcane, plus a lingering note of preserved plum candy; the strength is medium and the acidity, sweetness and bitterness are balanced;

At a coffee-to-water ratio of 1:15 the coffee liquid has the lightest color and a thin body, with only a little acidity from black plum and berries; the taste is flat, but there is almost no bitterness.

From the comparison above it is easy to see that the 1:8 ratio, because it uses less water, leaves the coffee flavors without enough room to express themselves and easily shows the negative trait of being heavy and bitter; the 1:15 ratio, on the other hand, because it uses more water, over-dilutes the soluble matter, so the coffee lacks body and naturally tastes thin and bland.

Among the 1:10 and 1:12 groups, the cold brew made at 1:12 clearly has the best flavor and mouthfeel when drunk straight, but Qianjie gives priority to 1:10 in many articles and in daily production. Why is that?

Finally, to keep the cold brew at a cold temperature, besides serving it in an iced cup, Qianjie usually also adds 1 to 2 hard ice cubes, so that even if the coffee is diluted, the flavor will not change too much; second, because every guest has different taste preferences, some liking it light and some liking it strong, the coffee tastes full and rich when the ice is first added, and as the ice slowly melts into water over time the coffee gradually becomes lighter, so using a high-strength cold brew with ice satisfies both the "strong-taste camp" and the "light-taste camp".