Lesson 8 - Mashing End of Unit SAQ

*** With reference to the process and technology used, discuss the advantages and disadvantages of isothermal, decoction, and single-vessel temperature programmed mashing.

Response

Isothermal mashing advantages

Isothermal mashing is the simplest form of mashing. The equipment used is relatively simple and costs less than that required for the other two forms of mashing. It also uses a lower cost mill and is easy to perform manually. All of these factors mean it is the best (and often the only practical) form of mashing for small breweries. The mashing in temperature of isothermal mashing can be high enough (if < 65°C) to minimise the operation of LOX enzymes in the mash. As it is a thicker mash than the other two methods, pH buffering is also greater in an isothermal mash.

Isothermal mashing is a shorter process than decoction and temperature programmed mashing, where a number of temperature stands are completed. However, as wort separation is undertaken in the same vessel, the total time taken for wort production in the one vessel is longer than most single-vessel temperature programmed mashes. Isothermal mashing uses the least energy of all the mashing methods. The gentler handling of the mash in isothermal mashing means that worts produced are lower in lipids and polyphenols. This can benefit the foam and colloidal stability of the beer produced. The gentler handling also means that wort viscosity does not increase due to shear forces on the mash, which is very important as the viscosity is already higher in isothermal mashing owing to the lower water to grist ratio.

Isothermal mashing disadvantages

Isothermal mashing requires well-modified malt, which tends to come at a higher cost and may not always be available. This means that if well-modified malt is not delivered or not available, problems with wort separation, extract recovery and downstream problems with the beer will be encountered, which isn’t the case with the other two methods. Isothermal mashing provides the poorest extract efficiency of all the mashing methods. Control of fermentability is limited with isothermal mashing, although if the process is performed consistently, fermentability will remain consistent.

Isothermal mashes need to be fed into the mash tun from above the vessel, and the filter bed needs to be suspended in the wort so the process allows significant oxidation of the mash. This means the shelf life of the beer is reduced. Although this is mitigated to a degree by the inactivation of LOX, the effects of autooxidation alone can still give the beer comparatively poor flavour stability. The use of adjuncts in isothermal mashing is restricted to pre-gelatinised products. Because of the many constraints, we have described the range of beer types that can be brewed successfully with isothermal mashing is relatively narrow.

Decoction mashing advantages

Decoction mashing provides good control of fermentability with both highly fermentable and minimally fermentable worts possible. It can process under-modified malt effectively to produce worts that lauter quickly. Decoction mashing is capable of producing worts with good levels of FAN and good foam stability. Due to the boiling part of the mash decoction, mashing can also reduce the concentration of DMS and its precursors. Boiling also helps extract β-glucans and proteins for degradation in the main mash.

The way in which the mash is handled is likely to form flavour compounds not formed in the other mashing methods, so decoction is likely to lead to a product with individual characteristics. There are also potential marketing benefits from using an elaborate and traditional approach. With maltase mashing, decoction allows us to produce a specific wort sugar spectrum while brewing in accordance with the Reinheitsgebot. Decoction mashing can produce higher extract recovery than the other two mashing methods. Adjuncts with a higher gelatinisation temperature can be added to the first decoction and boiled to gelatinise their starch, so there is more flexibility on adjunct use than is the case with isothermal mashing.

Decoction mashing disadvantages

The main disadvantage of decoction mashing is the amount of energy required to carry it out. It uses roughly 11.0 MJ/hL for single decoction mashing and 11.6 MJ/hL for double decoction mashing compared to 8.5 MJ/hL for single-vessel temperature programmed mashing. Isothermal mashing will be lower still. Decoction mashing uses the greatest number of vessels out of our three methods, so it is the most expensive option in terms of capital costs. The boiling of the mash increases the thermal load on the wort, so it is likely to reduce flavour stability. This also causes a pickup in colour and flavour that might not be desirable. The high temperatures and additional processing of the mash increase the dissolution of lipids and polyphenols in the wort, potentially reducing foam and colloidal stability. Decoction mashing can also take the longest of the mashing methods under consideration, with triple decoction mashing taking around six hours.

Single-vessel temperature programmed mashing advantages

Single-vessel temperature programmed mashing gives us the greatest control of the mashing process and allows us to process poorly modified malt and better cope with malt which doesn’t match our specifications. It is the most flexible mashing method and gives excellent control of fermentability, FAN and the breakdown of proteins that help stabilise foam. We do need to know the degree of modification of the malt to be able to ensure control is effective. Single-vessel temperature programmed mashing adds less thermal load to the mash than decoction mashing and avoids excessive colour and flavour pick up and lipid and polyphenol extraction. It is the most technically advanced method of mashing, so the equipment available to undertake it provides excellent control of oxygen and shear. This provides good flavour stability and easy wort separation. Single-vessel temperature programmed mashing gives the best extract recovery of all the methods, although this is only marginally better than that of decoction. We can undertake maltase and jump mashing using single-vessel temperature programmed mashing to make beers of specific characteristics. Single-vessel temperature programmed mashing can produce mashes that will process efficiently and effectively in both lauter tuns or mash filters.

Single-vessel temperature programmed mashing disadvantages

Single-vessel temperature programmed mashing requires more equipment than isothermal mashing and is not suited to manual control. The equipment requires more maintenance and calibration checks than the equipment used for the other two methods. For processing adjuncts with higher starch gelatinisation temperatures than barley large starch granules, an additional vessel is required to gelatinise their starch, although these integrate well with the method.