Steam is a great carrier of heat and because it is at 100C to 200C in non contained systems, it can heat quickly without scorching. When superheated, it penetrates the fluid well beyond the boundary layer, and when a central manifold is used, it gives great convection and gelatinisation. (You still need to stir a grain mash for even temp, not to prevent scorching) It isolates the very high temperatures of the burners from your wort, while injecting heat without the usual boundary layer problems.
1 litre of water raised to 100C contains 419 kilo Joules of energy (sensible heat)and weighs 1 kg. Specific heat of water = 4.19 kJ/1C/litre, specific heat of steam = 2.16 kJ/1C/kg. 1 kg of steam at 1 atmosphere and 100C contains 419kJ (sensible) + 2257 kJ of heat of vapourisation (latent heat) and occupies 1,673 litres!
So, it gives off lots of heat when it condenses and expands *very* rapidly when vaporised.
100 litres of water at 40C, to be raised to 60C quickly,(G.Fix's mash) needs (20C x 4.19 x 100) 8,380 kJ of energy. This means 3.4 kg of steam, or 3.4 litres of water vaporised and injected into the 100 litres.(makes 103.4 litres) If you needed to do it in 15 minutes, the steam generator would need to absorb (8,380kJ/900secs) 9.3 kiloWatts (32,000 BTU/hr) At a home setup efficiency of about 40%, you would need a 24 kW (82,000 BTU/hr) burner. I use a 22 litre pressure cooker as my primary steam boiler and a 40 kW burner for 85 litres.
Now there is WET steam and DRY steam, and SATURATED steam and SUPERHEATED steam. Wet and dry is easy, dry is 100% water *vapour*,a colourless gas, wet steam contains water droplets. (the stuff clouds are made of) Saturated steam is steam at the boiling point of water at that pressure. i.e. If the temp drops a tiny bit or the pressure goes up a tiny bit, it condenses. Saturated steam is just steam, it is at the point of condensation. All boiling chambers usually produce steam that is 98% saturated vapour and 2% water droplets, i.e. it is "wet" and "saturated". This is important to remember. The % dry is called the steam "quality".
Superheated steam is steam above the temperature of saturated steam for a given pressure. The STEAM TABLES will give the temperature of saturated steam for any given pressure, or vica versa. Thus 1 kilogram of superheated steam at 1 atmosphere and 150C has total heat = 419kJ (sensible) + 2257kJ (latent) + 105kJ (superheat)= "specific enthalpy" of the steam.
Example of Steam Tables
Pressure Temp Sensible Latent Enthalpy Volume Atmos oC kJ/Kg kJ/Kg kJ/Kg m3/kg 1 100 419.04 2257 2676 1.673 2 120.42 505.6 2201.1 2706.7 0.881 3 133.69 562.2 2163.3 2725.5 0.623 4 143.7 605.3 2133.4 2738.7 0.461
When we produce steam in a domestic pressure cooker (with the weighted safety relief valve operating normally please, don't touch it!) it is wet and saturated. Our mash tun and the piping's resistence to flow provide some back pressure, but essentially it is not a contained PRESSURE system and generally doesn't fall under the STEAM REGULATIONS. (These are very heavy, rightly so) However our system does cool the steam in the piping and manifold, so some condenses. This can lead to a dangerous condition called "water hammer" where condensation collects and blocks the fast flow of steam and builds up dangerous back pressure, causing further condensation. This can easly rupture equipment if you have tampered with your safety relief valve. Remember 3 kg of steam in 15 minutes is 4,800 litres of steam, that is 5 litres/second, don't stand in the way!
However superheated steam is well above condensation temperature for the low pessure of an open, uncontained system and ensures that high quality dry steam reaches your mash or kettle. Heat losses to piping are absorbed by the superheat.
To "rolling boil" 100 litres of wort for 1.5 hours. In a normal vigorous boil you would expect to loose 15% of volume. Gee, this is exactly how much steam you need to generate to supply the necessary heat. Boil 15 litres of water to 15 kg of steam and inject. Because it condenses and then heats the water to boil the same ammount, in a perfect system there is no loss of volume. But because there are other heat losses, saturated 100C steam can't effectivly boil water at 100C. However 150C superheated steam would boil it and add a further 1620 kJ of energy, boiling off 2/3 a litre of wort in a perfectly insulated system. Conclusion, you can boil without scorching and get a good rolling boil with steam injection, but you can't reduce volume much. Result, smoother paler beers and a need to sparge to exact volume.
Remember to becareful about constriction of steam flow. If the back pressure is too high and you open the control valve suddenly, you drop the pressure in the vessel instantly, superheating the steam inside. This superheat will vaporise more steam, causing some tendency to boilover out your control valve. Start at 1/2 inch basic, and scale up with bigger volumes.
An important startup step, boil your water with the relief valve open for a few minutes to expell O2 (and Cl). This will otherwise corrode your system and HSA your wort.
This problem could be in your RIMS unit, mash tun or kettle. Such flavours and colouring are often desirable, some people throw white hot rocks in their wort to get these reactions! However, these Maillard (browning) and Caramel reactions not easy to control at this interface (scorching) and I think are best controlled is seperate decoctions. Steam injected into another pressure cooker of decoction is my preferred method. A RIMS unit of a steam injection manifold inside the recirculating pipe is an idea of mine. If the pump was below the injection point (to avoid cavitation), the pump speed would be irrelevant to scorching, allowing very light recirculation. Just a recirculating pump with a normal mash injection manifold would give exactly the same result.
If steam is injected into a unstirred settled mash from beneath the grain bed, it temporarily heats the bed to 80c -> 90C before dissapating into the thinner parts. This gelatinises the starch globules well without a decoction of the colour increase of a decoction. Rapid and complete conversion is enhanced.
In conclusion, steam is powerful and precise, a gentle heating method but dangerous without proper understanding. I urge you to get a competent engineer to check your constructions if you harness it's power.