The temperature profile for all percolation brew methods tends to increase to a maximum during the dilution phase and then, at the moment the slurry is at its fullest level, the temperature slowly declines again during the drawdown. As we discussed in Lesson 1.01, the thermal conductivity and the specific heat of the filter cone will affect how much of a decline occurs. The flow rate and the thermal mass of the slurry also affect the rate of decline of the temperature profile. Slower flow rates mean the volume of liquid in the slurry declines more slowly, so the thermal mass of the slurry will be greater.
To observe some trends in the temperature profiles of certain percolation recipes, we conducted an experiment using only brew water and no coffee to explore to what extent the level, thermal mass, impacts the temperature profile of a percolation brew. At 15-second intervals, we logged the temperatures of two separate brew-cycles using a mechanical brewer. For the first cycle, we tested 250 ml of brew water. Then the second cycle was for 500 ml of water. To simulate a flow rate similar to a typical percolation brew, we used a Wilfa Svart brewer and filter cone which allows for the exiting flow rate to be adjusted. We set the aperture on the Wilfa cone to the lowest setting. In the chart below, you can see the results of the experiment. As you would expect, the larger brew declined in temperature significantly more slowly than the smaller brew.Time 250ml Temp °C 500ml Temp °C 0:15 90.4 90.7 0:30 89.1 90.1 0:45 86.9 89.5 1:00 85.5 89.1 1:15 83.4 88.5 1:30 74.3 88.1 1:45 End 87.5 2:00 85.1 2:15 83.0 2:30 82.8 2:45 80.9 3:00 76.3 3:15 End
The temperature of a pour-over is reduced considerably by the large amount of surface area open to the outside air.