Lesson 7 - Mashing Technology SAQ
This lesson provides the opportunity for you to test yourself on the material covered in Lesson 6 on Mashing Technology and determine the level to which you have attained the expected outcomes.
SAQ Suggested Response - Q3
**With reference to the common types of heating jackets, describe how the design of mash heating jackets affects heat transfer to the mash.
Response:
How the jacket is designed has is a significant impact on the rate of heat transfer into the mash. Larger jackets provide more area for heat transfer, hence transferring more heat than smaller jackets given the same conditions. The difference between the temperature of the mash and the temperature of heating medium is also significant. A higher temperature heating medium like the products of combustion will heat mash faster than hot water at atmospheric pressure. So if the design of our jackets allowed for a higher temperature heating medium, they would transfer more heat. In the case of steam and hot water, the greater the pressure, the hotter the fluid so jackets that can withstand high pressures can deliver more heat.
The greater the velocity and degree of turbulence in the mash and heating media, the greater the transfer of heat. Dimple jackets increase turbulence in the heating medium as flow through them is torturous. If jackets have the dimple jacket facing into the mash, they can also develop micro-turbulences in the mash. Conventional jackets can be fitted with baffles and spray nozzles to increase turbulence inside the jacket. The flow through half-pipe jackets is not usually turbulent, but high heating media velocities are possible to improve heat transfer.
The thickness of material between the heating medium and the mash affects the rate of heat transfer. The installation of dimple jackets provides increased stability to the vessel shell so a thinner wall material can be used. As they have no structural duty, dimple jackets are thinner than the vessel wall, so they can be fitted with dimples facing into the mash to improve heat transfer. It is not possible to reduce the thickness of wall material with half-pipe or conventional jackets.
Any fouling on the jackets acts like insulation, reducing the rate of heat transfer. Jackets could be highly polished to reduce the ease of fouling. Although this is not typically done as the benefits are marginal and the polishing is quickly dulled.
Finally, the thermal conductivity of the jacket surface influences the rate of heat transfer. If we were to use a material like copper with a higher thermal conductivity, heat transfer would be improved versus stainless steel. Copper is not a suitable material of construction for modern brewhouses, so this approach is not used.