Method 2/ George de Piro/Noonan's method above. Place a little wort in the kettle and thicken. But *stir continously* and do not continue rapid evaporation after the increasing extract concentration reaches a boiling point of 110-130C (test with thermometer). Add more water or reduce heat to accomplish this. Continue ~20 minutes. Maillard reactions and Caramel molecular dehydration will take place.
Method 3/ Place total wort in a 25 litre pressure cooker and bring to designed maximum temperature for ~3-5 minutes. Release steam, uncover and boil normally for 60 minutes. Rapid and complete hot break, very dark but smooth Maillard reactions, and very high bittering hop isomerisation are the result of this. Very little caramelisation as sugar concentration is much lower than 1 and 2.
I have used methods 1 and 3 with great success. I have never tried 2. Acidifying the mixture, or adjusting the sugar concentration will also change the result.
Why does the temperature rise so rapidly? Basically heat flow from flame or element to wort meets different resistances. The thermal conductivity of the metal (expressed as "coeficient of heat *transmission*") in the kettle wall, and the transfer resistances (expressed as "coeficient of heat *transfer*) at the gas/metal and the metal/wort interfaces. Of these, the transfer resistances are about 90% of the barrier because metals have good transmission qualities. The gas/metal is the highest of these resistances.With *turbulent flow* conditions (i.e. no boundary layers) this is a rough heat distribution diagram.
o oo oo o o o o o oo o o o o oo o o o o oo oo oo o oo o oo o o oo ooo o o WORT at 100C oo oo o ___________________________________ ///////// METAL at 110C ////////// __________________________________ () () () () () () () () () () () HOT GAS at > 950C
However if the wort is not moving turbulently, it forms a boundary layer on the surface of the kettle. This is a problem because the *transmission* coeficient for water is lousy. The boundary layer then heats up and begins to form a viscous caramelly layer which has less heat transmission properties. This reaches PYROLYSIS temperatures and a classic scorched layer of high temp Maillard products and carbonised cement forms on the kettle. This has less heat transmission properties and very poor heat transfer properties and so on. The temperature distribution diagram looks like this.
o oo oo o o o o o oo o o o o oo o o o o oo oo oo o oo o oo o o oo ooo o o WORT at 100C oo oo o ------------------------------------ ***Carbonnised cement at 250C****** _____________________________________ ///////// METAL at 350C ////////// __________________________________ () () () () () () () () () () () HOT GAS at > 950CAnd the burnt acrid flavours enter your wort, including a few toxic ones. Stir like hell or form your Melanoids in a steam environment like in a bowl in a pressure cooker.
Charlie (Brisbane, Australia)