Making rich, mellow cold-brew coffee at home is simple—if you have the patience. Ground coffee needs hours of steeping in room-temperature water to allow carbon dioxide gas to slowly exit the nooks of the coffee particles and the water to penetrate into the particles and extract flavor. So, if you have a sudden hankering for a cup, you’re pretty much out of luck.
That is, unless you have a home vacuum sealer. We’ve found that a sealer with a jar-lid attachment can make short work of that slow cold-brew process, forcibly drawing out the CO2 so that the water floods the grains and steeps a full-bodied brew in just 15 minutes. Here's our method, which yields about a quart of concentrate.
1. Combine 2½ cups (200 grams) medium-grind coffee with 5 cups room-temperature water in ½-gallon widemouthed Mason jar and stir until all grounds are wet.
2. Place vacuum attachment on jar and apply vacuum. Stop machine before rising froth reaches top of jar. Release suction by gently removing and replacing hose.
3. Repeat step 2 until coffee froth stops rising significantly. This may take 10 to 15 repetitions, depending on freshness and grind of coffee (fresher beans and finer grinds release more CO2).
4. Stir mixture and let stand for at least 5 minutes. Pour through fine-mesh strainer set over large measuring cup, then strain mixture again through paper coffee filter set in coffee cone into 1-quart container with tight-fitting lid.
5. To drink, dilute to taste (a 1:1 ratio of concentrate to water is a good starting point) before adding ice and milk or sugar as desired. If not using right away, affix lid and refrigerate.