The process of ‘making coffee’ is just a process of relying on osmosis to extract chemicals from coffee beans into water. If you use a French press you are using heat to accelerate the process. Espresso adds pressure to further reduce the time to that tasty cup of coffee. Though the process of cold brewing coffee goes the other way, by removing the desire for a quick cup of coffee you can let water do its own thing.
First I should state that I am by no means an expert. What I will describe here is just my process. Also I should note that I do not measure much in the kitchen. Just like my grandma I do most things by feel. Please take this as a guide and experiment; see what works for you.
Remember that this is just coffee. It’s cheap to play, so play!
To start, I use an old peanut-butter jar purely because it was what I had at hand. Any non-reactive resealable container will work just as well. Unlike other methods of brewing, you are not making just a single cup of coffee. I find my jar provides me with a few days’ worth of coffee extract. As you play you will find what works for your particular coffee habit.
With a containment device sorted, the next step is beans. I tend to use a fine grind. My thinking is that I will get a more complete extraction due to the greater surface area, though I have no evidence to back up this hypothesis. These grounds then go in to the peanut butter jar, about an inch of grounds in a 7 inch jar, so let’s say a 1:7 ratio of coffee to water.
Next step is the liquid: just simple water. As with any beverage, use water that you will enjoy drinking. Remember that this is the majority of your final beverage. If you do not like what comes out of your tap, then filter it.
I add enough water (let’s say 1/3 full) to cover the grounds. At this stage the goal is to just make sure that all the grounds are wet. By adding only enough water to cover at this step it allows me to swirl the water to make a slurry and look for dry pockets (difficult without a clear vessel). If you need, grab a spoon or chopstick and make sure that there are no dry pockets. It would be a shame to miss out on any coffee goodness which could be extracted.
Once everything is wet, top off the vessel with water, and seal it up. Most of the time I put it in the fridge though this is mostly to make sure that it is out of the way. If you have counter space then room temp will work just as well. Again this is another variable that you can play with as the main goal here is to let the water do the extraction over time.
Then we just let it all sit. Because this is a slow process, there is less risk in missing on the timing. I have done runs as short as 18 hours and as long as 48. I have found that 24-ish hours is a sweet spot, just enough time to let the water do its thing completely and not so long that I forget about it. For me the beans play a much larger role in determining the outcome then a few hours on either side. However I bet that anything in the 12 hour or less range will tend to be a bit weak when it comes to the final outcome. If I remember I will go give the jar a shake or two throughout the day but I have not found that this is a strict requirement as osmosis is a very powerful ally.
Lastly, when you feel that your brew is done, it’s time to filter. If at all possible disturb the jar as little as possible as most of the solids will have settled in the bottom. Anything still in the jar is less that has to be filtered at this stage. I pour the content of the jar in to my French press without the filtering mesh (yet), and let things settle for a minute or two. Again the thinking is what is in the bottom here is not going to end up in my cup. From here I apply the press filter and pour thru another metal filter in to my final containment device.
For me having a separate brew and storage vessel gives me the flexibility to be brewing while still having something to drink. Though again this is not a strict requirement. When I was starting out I let the French press settle and then would rinse out the jar and just pour the cold brew back in to the same jar I brewed in. It’s glass, it doesn’t care.
So now that we have our coffee, what should it taste like? It might be my reliance on metal filters but my cold brew always has some fines. Therefore is a body to it that I do not get with other brewing methods. Also the words strong and mellow come to mind. It does have a bit more zip, though this is likely due to a stronger concentrate of all the coffee magic being extracted from the bean. There is a different flavor profile that happens with cold brewing when compared to a hot method, even for the same bean. I am guessing that there are some elements that just can not be extracted in the cold, or possibly are destroyed in the hot. For example, I do not get much of the tannic bitterness that I find with the hot methods. If you like an acidic cup of coffee, this is not the process for you.
Lastly, what can you do with this stuff? The trick is to stop thinking of this as coffee to be had one cup at a time. Cold brew becomes an ingredient to be added to things. Like your coffee warm? Use 1/2 cup cold brew and 1/2 boiling water and now you have a cup of “drip” coffee. Rough day at work? 1/2 cup cold brew, a splash of water and 1/3 cup of low-shelf whiskey. Got the post-lunch-naps? 1 shot straight up. The possibilities are nearlyendless when it comes to what this stuff can do.
So there you have it: cold brewing. Enjoy!