Low Thermal Stress (LTS) Brewhouses
Heat transfer and thermally-driven organic reactions are essential to the brewing process.
Heating is used for very different outcomes in brewing and it drives many reactions, both wanted and unwanted.
Boiling wort drives the competing outcomes of:
- Isomerisation of hop alpha acids to their bitter form./ Complete Denaturing of isomerised alpha acids into their subsequent bitter and astringent form.
- Coagulation of unwanted haze-forming proteins and partial denaturing of foam-positive LPT1 and k proteins. / Complete denaturing and precipitation of essential foam-positive LPT1 and z proteins.
- Formation of desirable volatiles originating from malt and hop products./ Evaporation of desirable volatiles originating from malt and hop products.
- Formation of unwanted volatiles (UVs): di-methyl sulphide, hexanal, 2-furfural, B-damascenone, phenylacetaldehyde and 3-methylbutanol. (+ others)/ Evaporation of UVs di-methyl sulphide, hexanal, 2-furfural, B-damascenone, phenylacetaldehyde and 3-methylbutanol. (+ others)
The LTS boiling process aims to:
- Keep boundary layers near heating surfaces as low as possible by performing half the “boiling phase” below 98C, leading to gentle partial denaturing of the LPT1 and k proteins to hydrophobic stage. Two of the UVs, Beta-damascenone and 2-Furfural, do not evolve at this temperature, and both are hard to strip at boiling temperatures. (furfurals are used as solvents in epoxy glues, herbicides and are lethal to rats @ 65mg/l)
- Maintain heating surface /hectolitre above 0.30 m2 to reduce delta T between heating surface and wort.
- Perform rapid stripping of unwanted UVs at temperatures over 100C for about 45 minutes with a double/triple spreader fountain. Enhanced stripping is the only method to reduce 2-furfural.
- Partially denature LPT1 and k proteins into their hydrophobic foam-positive form so that they remain in solution and support foam at dispense. Ultimately LTS systems completely denature and precipitate about 40% of all LPT1, compared to 70% with conventional boiling. (ref: ASBC)
- Boil hops no more than 45 minutes, at which point they rapidly increase denaturing into their astringent yet bitter form.
- Arrest the post-boil evolution of UVs by crash cooling wort to 88C during whirlpool. Each 5C reduction from the 103C boiling temp halves the DMS evolution, so 88C means post-boil DMS formation is about 1/8th the rate during boiling. Below 88C affects hot trub formation negatively.
- Reduce the thermal stress indicator, the delta Thiobarbituric Acid Assay (TBA), to below the German standard of 15. This optimises the reduction of non-volatile staling aldehydes and imines.
Brewmax’s design of a pumped external calandria with double/triple, vented fountain returns is ideal for LTS. This rapid stripping of UVs allows shorter nucleate boiling times and thus more time below 98C.
Designing the kettle to act as a crash-cooled whirlpool reduces evolution of post-boil UVs by reducing the rate of formation and the time at elevated temperatures post-boil.
Casting out to the heat exchanger from multiple outlet levels also reduces the time at evaluated temperatures, further reducing post-boil evolution of UVs.