Low Thermal Stress (LTS) Brewhouses
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.