I’ve experimented with a slow stock this week (I’ve just finished a 3-day beef stock). The process is an interesting one; water is kept at barely a simmer and is reduced until more water is needed and the cycle continues. As part of my experiment, I wanted to see just how low the heat could be to constitute a ‘slow simmer’
The photo above shows my pot of stock after losing 4 liters (quarts) of water in 12 hours. The ‘scales’ on the side include some fat residue and a lot of dried tomato skins which I use in lieu of tomato paste.
How slow was the simmer that reduced this pot by half? It was hardly bubbling at all; a bubble may come to the surface every few minutes.
Water can never get above 212 degrees Fahrenheit (without pressure). At 212 degrees it changes state into a gas at which point it produces bubbles (and you see steam). A rolling pot of water is no hotter than one at it’s slowest simmer.
A full boil would have reduced this pot faster (I imagine this is due to the different temperatures in the pot – I suspect the stock nearest the element was hovering at 212 and cooling by 1-2 degrees as it rose through the pot) but the water would have barely been any warmer than it was. It would have also moved the ingredients around rapidly which could produce more sediment and emulsify the fat into the water (making it harder to remove).
This low temperature is a little ridiculous (although it allowed me to leave the pot without close monitoring for longer periods of time) but it’s often beneficial to cook ingredients at a very gentle simmer as it offers all the same heat benefits without circulating the ingredients into mush. An ideal slow simmer has a constant but very gentle stream of small bubbles.
Do you agree or do you think differently?