All pour over brewing methods suffer from heat loss. The majority of this loss comes from the open top of the cone. Some pour overs aim to minimize the loss at the sides with thick walls surrounding the filter, however this can lead to reduced temperature retention.
It sounds counter-intuitive, so we conducted some tests…
The glass cone measured lower in brewing temperature during the first minute and continued to rise throughout the brewing phase. AltoAir had higher initial temperatures and these stabilized earlier during the pour. Peak temperatures reached in the cone were the same, whilst average brew temperature in AltoAir was higher.
The reason why; Glass and ceramic cones have greater thermal mass and require more energy to heat up, so during the first 90 seconds they actually pull heat out of the brewing coffee. AltoAir’s minimal structure has very little thermal mass to heat and a greatly reduced contact area to conduct the heat energy away.
Filter paper placed in brewer, 200g boiled water poured to wet filter and pre-heat cone & cup for 1 min. 15g coffee, 250g water at 96°c & added to cone during 2 minutes (bloom stage omitted for clarity of results)
Brew conditions, (grind, pour speed etc.) were identical for both devices.
Temperature measured in the cone until dripped through, then measured in the cup.