Types of Mashing systems
Three main mashing systems are operated:-
- Infusion mashing
- Decoction mashing
- Temperature programmed mashing
- Infusion mashing is the classic British methodology for ales and stouts, using well-modified malt and relatively simple instrumentation.
- Solid mash ingredients are mixed with hot brewing liquor to gain a mash temperature of 62–65°C.
- Mixing is performed during passage to an insulated unstirred vessel, the mash tun, which is 7–9 m in diameter and 2m deep.
- In some breweries these traditional vessels have been superseded by mash mixers.
- The mash incorporates a liquor to solids (grist) magnitude relation of around 3: 1 and this thick mash helps to stabilize some malt enzymes.
- Infusion mash temperatures are suitable for starch degradation, but malt b-glucanases and proteases are rapidly inactivated; hence the requirement for well-modified malt whose cell walls and proteins have already been substantially degraded during malting.
- Mashing lasts for 1–2 h and is followed by mash sparging.
- This involves spraying water at 70–75°C onto the surface, which percolates through the grain bed and washes out the soluble extract.
- The grain bed sits on the false bottom of the mash tun, that has slots approximately 1 millimetre wide.
- These are kept clear by the large husk fragments in the mash that has as a filter aid.
- Resultant liquid extract is called ‘sweet wort’.
- Sparging is continued until the particular gravity of the wort falls to a specified level indicating that tiny or no more soluble sugars remain in the mash.
- Decoction mashing is very old and traditionally used in Europe and is suitable for less well-modified malts.
- The initial mash temperature starts at around 35–40°C, with a liquor to grist ratio of up to 5 : 1.
- This initial lower temperature facilitates more extensive hydrolysis of β-glucan and protein, and is often called a ‘protein rest’.
- The temperature is then raised to 50–55°C, by removing a portion of the mash, which is boiled and immediately returned to the mash vessel.
- This may be repeated once or twice more, with intermediate holding periods.
- The aim is to raise the temperature stepwise to about 65°C, to achieve starch degradation, and finally to 75°C.
- Wort separation is usually via a lauter system, aided by rakes or knives that cut the grain bed; alternatively, mash filter systems may be used.
Temperature programmed mashing systems:
- Temperature programmed mashing systems are well designed and operated by many modern breweries.
- The mash temperature is raised using a heating jacket from around 40°C to above 70°C through any number of holding stages.
- This allows much greater control over the mashing process and the programme can be adapted for variously modified malts.
- Mash separation is usually through a modern lautering device or mash filter.
- The result of mashing, irrespective of the system used, is an aqueous extract, the sweet wort (for typical composition, and insoluble spent grains.
- The latter byproducts are highly perishable and are often quickly transported away for direct use as cattle feed.
- Attempts have also been made to generate further fermentable brewing sugars from the cellulosic components of spent grains using acid or enzyme hydrolysis.