In summer, I find it very difficult to bake bread, with temperatures easily exceeding 40° C (100° F). In winter, it's the opposite, and I've just found "the" solution for gently raising my leaven.
Place the sourdough on the espresso machine!
The temperature at which the cups are warmed rises to around 30°C (85° F), and I turn the machine on again every half hour or so.
My lеаѵеn rises happily, in 3 – 4 hours, and I have it in front of me so I can keep an eye on it.
Other solutions exist, the internet box (but it's already occupied by cats, and the temperature isn't as high), the oven (but you have to be careful that it doesn't rise too much), or the (luxurious) "risingbox".
My little empirical method has the advantage of simplicity and effectiveness.
How do I know the temperature?
This detail is not indicated in the technical data sheets for espresso machines (I've looked at about ten of them…).
But it is important: in my opinion, my 30°C (85° F) is the maximum.
First method: by placing your hand
It should feel lukewarm, but not hot. Yes, I know, it's as precise as your grandmother's measurements (a little sugar, you get the idea). And this feeling of 'lukewarm' depends on each person. But it's generally between 25°C (77° F) and 30°C (85° F).
Second method: using a contact thermometer
Simply place the tip of a cooking thermometer on the metal surface. This is how I got my 30°C (85° F).
Third method: by measuring the temperature of the jar
This is the most 'scientific' and, in any case, the most accurate. It's still done with a kitchen thermometer, but this time it's done directly on the jar, after it's been sitting in the espresso machine for about ten minutes.
I'll do it next time.
Warning: do not use a cup warmer
There are also USB gadgets that can be used to heat a cup. The temperature is much higher, 55°C (130° F), and not at all suitable for a sourdough (or even for a human being, because if you put your hand on it, you get a first-degree burn).
