Thursday, August 26, 2010

Vacuum Cold Brew

Jeremy and Linsday prepare the coffee.

Some discussions the other day over the internet prompted me to ponder the potential for vacuum brewing cold coffee. If marinades could be infused into proteins, pickling juice into vegetables and compression to fruits, what possibilities would vac bagging coffee yield? Could it lead to properly extracted cold coffee in a short time period?

With that in mind, we gathered the Ethiopian Yirgacheffe from Origins Organic Coffee that we're brewing at Spro in the cold brew tower. It's become our de facto standard iced coffee this summer with a crisp fresh flavor profile featuring notes of citrus and a reassuring familiar taste of "coffee." It's light and easy to drink and has been the panacea in Hampden for our hot Baltimore summer.

Ready for the chamber vacuum.

For this initial test, we chose relatively simple parameters: 48 grams coffee, 24 ounces cold water, vac bag at 31 mbar and just wait.

Initially, I was planning on leaving the bagged coffee overnight and then pull it out to see the effect. The concern there was that if I was going to let it steep overnight, then it doesn't really offer much of an advantage over the brew tower or other long-term brew methods.

Water temp 70.3F but I it feels cooler.

Instead, I opted to let the bag steep for ten minutes and then pull a sample. While the thermometer shown displays 70.3F I'm hard pressed to believe its accuracy because it was pretty cool to the touch.

Perhaps I should note that while it is possible to bag water and coffee with a Food Saver type of vacuum sealer, it is difficult and chances are that you won't get the proper flush of air from the bag, nor will you be able to set the vac pressure. A proper chamber vac allows greater control of the vacuum environment as well as a complete vacuum being set over the liquid.

Filtering the coffee with Hario V60 and AeroPress.

After ten minutes it was time to cut the bag open and give it a taste. However, the coffee needed to be filtered and we tried two different filtration methods: simple paper filter in a V60 Pourover and a pressurized filtration through an AeroPress.

The problem with pouring out steeped coffee are the sediments which gather in the filter. Normally, these are dispersed throughout the coffee bed, but lacking the coarse ground coffee, the fine sediment clogs the paper filters. The pressure from the AeroPress only improved filtration speed slightly.

V60 and AeroPress filtered with the brew tower control sample.

The results themselves were less than stellar but proved insightful. At ten minutes under pressure, the coffee had been extracted but was still underextracted. The color variations in the samples above demonstrate this. The flavor show hints of the tower brew but was very faint.

No conclusions as there's still much to be tested and tried, but it's a good start. Some thoughts were to go with hotter (100F) water or longer times. In the coming weeks we'll sample more and see how it goes.