Coffee is morning routine to start the day. Why not as a finish? Simply because the caffeine buzz will keep you up. This is where the rotavap come handy. Separating the desire-able to unwanted: capsaicin heat vs. flavor of chilies, bitterness of the pith vs. oils and aroma of citrus, and bitterness and caffeine vs. roasted floral qualities of coffee. Unfortunately, alcohol distilling is illegal and any restaurant willing to do so risks loosing it's liquor license. However, distillations can be performed for personal use to extract essential oils or water purification as long as the still or flask is under 1gal. I'll be getting those essential oils... For more information on what's going on, here's a Rotary Evaporator in the Kitchen Primer - Cooking Issues.
I started with the recipe basis from Modernist Cuisine approximating 1:3.75 ratio between citrus aromatic to vodka, but then cut back to 1:7.5 because of the beans high oil content and strong flavors. After grinding the coffee, I just mixed the grounds into the vodka hoping to get the floral qualities of a cold press coffee. Placed onto the rotavap, the machine is approximately set at 50mBar for 3 hours with a water bath at 40C.
Once started, constant monitoring of the flask rotation speed, pressure, bath temperature, and cold trap condenser temperature needed to be set to maximize yield. If you can smell the aroma of your distillate, you are losing flavor your cold trap is to warm. If the pressure is too high, the evaporation flask can boil over spoiling your final product. If the bath is too warm, the distillation can boil over or gain "heated" flavors. Flask rotating too fast and the distillate will splash about the evaporation flask. Properly configured, evaporation occurs smoothly at a relatively quick rate, drip by drip. I took my time on this distillation and turned off the water bath completely and made a few interesting observations. With the cold finger condenser set constant at ~0C, the only variables were vacuum pressure and distillate temperature. Maintaining a slight boil in the evaporating flask, the temperature of the water bath slowly dropped. Eventually, vacuum pressure measured 39mBar at 22C probably due to evaporative cooling.
After 2 hours of distillation and monitoring, pressure was released and the rotavap was stopped. What remains in the flask and the final extract. The remains in the evaporator flask tasted extremely bitter, astringent, burnt, and unpleasant. Although highly concentrated, the receiving flask, smelled of warm coffee and flowers.
Determining proof and alcohol concentration were seemingly difficult. Every resource references beer brewing and fermentation. Upon simpler observation, a comparison of sample density to water/alcohol mixtures was very easy as well as comparing the liquid yield to the final and initial contents, or determining continuity, the first process learned in fluids. Approximated at 99-100% or 200 proof.
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