I Make Cold Brew Coffee

I had two objectives in making cold brew coffee:

• To compare it with my regular drip coffee, and,
• To compare three different coffees to determine which was best, i.e., which one I liked best as cold brew compared to which one I liked best as drip.

My jars are labeled  (T)omoca, (M)esgana and (S)undried Sidamo.

Equipment Note: the scale was my Dad’s when he was chief chemist in a laboratory and measures accurately to a tenth of a gram. The jars hold a little over 200 ml and are former jam jars with a wide mouth and tight-fitting lids. The grinder is a Baratza Encore usually set at 22 for pour-over and drip and set at 40 for cold brew. The filter basket is from my Bonavita drip coffee maker with a paper filter (wetted before use).

For a full batch (not a test like this) I will use a 32 fl oz Bick's pickle jar.

I followed HomeGrounds’ instructions as follows:

1. Water and Coffee

I measured water and coffee as shown in the table below (all three coffees are medium roast, but there is medium and then there is medium. I have very hard water where I live (the city is built on limestone), so long ago I installed a Culligan drinking water system – almost as good as the aquifer from which a friend of mine gets his drinking water.

The Mesgana beans are lightest in color and gave the smallest volume. Sundried Sidamo beans are slightly darker and had slightly more volume while the Tomoca beans are very dark and their volume was about 50% more than Mesgana. Tomoca’s medium roast would be a medium-dark tending to dark for anything other than an Italian/French roast.

2. Grind your beans

I ground all my beans as coarse as possible – 40 on a Baratza Encore grinder.

My water:coffee ratio was to be the 1:5 recommended by HomeGrounds. To fill the jar as close to the top as possible I first measured the volume of liquid I would have (grounds + water ~250 mls) and settled on 200 mls of water to 40 gms of ground coffee.

Mistake No. 1. When ground, the Tomoca beans filled more than one third of the jar. I knew that 200 mls of water on top of that would exceed the capacity of the jar. Except that I forgot an elementary fact – there is lots of space between the grounds that will be filled with water and they also absorb water. I reduced the coffee to 30 gms and water to 150 to maintain the 1:5 ratio. This left a large space at the top of the jar and to fill it I added 50 mls of water and, as I didn’t want to grind an extra 10 gms of coffee, my ratio ended up at 1: 6.7.

3. Put all in a jar

The volume of the Mesgana and Sundried Sidamo at 40 gms would have been perfect for the jar as their volume (dry) was quite a bit less than that of Tomoca. To keep everything the same I used the same water and coffee amount for all three as shown in the table and in the photo below.

I first wetted the coffee with some of the water and stirred it well with a spatula and then added the rest of the water. This filled the jar close to the top with a foul-looking brown slurry of coffee grounds and water.

Ground coffee (top left), coffee slurry – side (bottom left) and top (right)

 4. Let steep for 12-24 hours

All three jars went into the outdoor fridge, aka my garage, where the night temperature in late April was -2C (28.4 F). Since the temperature was lower than typically in a fridge (~3C / 37F) I left the jars to steep for 18 hours. For 3-4 hours at the beginning and end I turned the jars a couple of times once an hour to ensure they wouldn’t pack down on the bottom. 

5. Filter into a clean jar

I poured the coffees through a fine sieve which removed the coarse coffee grounds and then filtered the first jar of coffee through my drip machine's paper filter.

Mistake No. 2: I knew that there would be fine coffee grounds remaining after the first filter. What I didn’t know was how fine those remaining grounds would be. They ranged from fine, but individually visible, to so fine they almost instantly formed a sludge on the bottom of the filter paper (below) and almost brought the filtration to a halt it was so slow.

Since it was obvious that some of the remaining grounds were heavy enough to settle quite quickly I left all three, partly filtered coffees, to settle over-night and filtered the remainder the following morning. I think this can be shortened to an hour or so, depending on the volume of liquid you are filtering, but I had the time, so let everything settle nicely for about 18 hours.

I decanted each coffee very carefully into a new, wetted paper filter and it went through in a few seconds. The remaining very fine sludge wasn’t worth filtering and I tossed it. I used new filter paper for each of the three coffees.

6. Dilute with water etc.

For the first trial I diluted each cold brew in a ratio of 1:2 coffee to water.

 Conclusions

• Making cold brew is easy and fast (leaving out the steeping time). I took so long because I was making three batches at the same time and taking photos and notes at the same time.
• HomeGrounds recommends a 1:5 ratio of coffee:water as a good starting point. My 1:6.7 diluted 1:2 with water (also a Homegrounds’ recommendation) resulted in a too diluted coffee. You would have to have a much more refined palette than mine to detect the nuances of each brew. Next time I will make sure I start with 1:5 coffee to water.
• Two stage filtering speeds things up immensely; if you have time, after the first filtering with a sieve, let the coffee sit for a few hours to let the remaining grounds settle and then decant slowly for final filtering.
• I have no opinion on length of time for steeping. That will require some testing. Below zero C is probably too cold for effective cold brewing. My next batch will be in the fridge.
• I have no opinion on whether I like cold brew better than my drip as I didn’t make a proper cold brew. I suspect I will like my hot coffee better, but the definitive answer will have to wait. My hot brew is almost always Mesgana (I like it smooth and easy) with Sundried Sidamo for a change.
• I prefer the Sundried Sidamo in this trial but remember, that’s a personal preference and it also wasn’t a proper cold brew.

Next Time

• Make some cold brew of Sundried Sidamo at a ratio of 1:5; brew at a slightly warmer temperature – approx.. +5 for 18 hours.
• Use my Bick's sauerkraut/pickle jar for a full batch
• Try the cold brew with hot water and hot milk at a ratio of 1:2