How fast can you brew? Are there any benefits to much longer brew times?
These are some good questions we often get and they have to do with the overall brew strength and extraction of the cold brewed coffee. In a previous blog post found here, we looked at the influence the grind size had on the brew strength and extraction. In this experiment, we're going to look at how the drip rate (and resulting brew time) will affect the brew strength.
The drip rate is definitely an important variable with Cold Bruer. From our development phase of the product, we know that there's a limit to how fast you can brew. Otherwise, patience aside, we'd likely be tempted to make a pot of cold brew in 6 minutes rather than 6 hours.
From our experience, we suggest brew times of around 5-6 hours for a proper extraction. In this experiment, we're going to look at brew times on both sides of this recommendation and see how it has impacted the extraction. For this experiment, we're going to look at 3-hour, 6-hour, 12-hour and 24-hour brews.
Coffee: Medium roast Kenyan from Artis (about 4 weeks after roast, so not super fresh).
Brew Water: 700ml ice/water (300g ice and 400g water)
Grind: Medium drip (7-F on Baratza Vario)
At a starting drip rate of about 1 second between drips, our brews take about 6 hours to finish. Based on this, we set the drip rate on the 3-hour brew to about 0.5 seconds between drips. For the 12-hour and 24-hour brews, we set the drip rates to 2 and 4 seconds between drips respectively.
It was pretty fun to watch them progress at different rates, and each appeared to be on track. Our 3-hour brew ended up taking a bit longer. A little over 4 hours. The 12-hour brew finished while I was asleep, but it looked like it was still on track to finish in time as I went to bed. The 6-hour and 24-hour brews finished on schedule.
Once the 24-hour brew finished the following day, we grabbed some people from our shared office space to taste the results. With a few differing opinions, most everyone had similar tasting notes about the cold brews. Our 24-hour brew tasted flat and tanic with a pretty unpleasant bitterness that lingered. The 12-hour brew had high initial acidity, and then went flat quickly. The crowd favorite was the 6-hour brew that most everyone found to be the smoothest and sweetest. The 3-hour brew had similar sweetness as the 6-hour brew, but it lacked the body, and tasted a little thin and watery.
After the qualitative tasting, we brought out the coffee refractometer to measure the brew strength for some quantitative data. The total dissolved solids (TDS) were measures as follows:
You can't rush a good thing! There's a certain amount of time required to make great cold brew, but too much time is not a good thing either. I'm curious what the results of the 3-hour brew would have been had the brew actually taken 3 hours to complete (definitely more on the thin/watery side). It was a bit surprising to see the drastic difference in taste between the 12-hour and 24-hour brews given that the brew strengths differed by only 0.04%. This makes me think there's something else at play than just the extraction...