How thermo-stable α-amylases work in adjunct liquefaction

Adjuncts such as maize (corn), rice, cassava and sorghum have very high gelatinization temperatures. Malt α-amylases are deactivated at high temperatures. Heat-stable α-amylases are not. They break down amylose and amylopectin to improve yields and reduce the risk of haze in the final beer.

Adjuncts containing starch with low gelatinization temperatures include barley, wheat and oats. These have gelatinization temperatures of <65°C. You can mash them together with the malt in the mash-tun. 

Adjuncts including maize (corn), rice, cassava and sorghum have much higher gelatinization temperatures. You may need to gelatinize these in a separate cereal cooker at temperatures of 85°C - 100°C. These higher temperatures deactivate malt α-amylases. That's why heat-stable α-amylases are often used for these types of adjuncts. Their activity isn't affected by high temperatures. 

α-amylases are endo-acting enzymes. They act on 1,4-α-glucosidic linkages in amylose and amylopectin, bypassing the 1,6- linkages.  Breaking these links reduces the risk of retrogradation. Retrograded starch precipitate means lower extract yields. It can also appear as haze in the finished beer.   

α-amylases also lower wort viscosity. That's because they break large amylose and amylopectin molecules down into smaller dextrins and oligosaccharides. 

Thermo-stable α-amylases are added to the cereal cooker with the adjunct at the start of liquefaction. If you're running a single-vessel brewhouse you can add them to the mash-tun with the adjunct at the start of liquefaction.