Originally Posted by jdlev
What's the purpose of the 15 minute step at 160 degrees?
From Homebrewing Wiki: German brewers commonly apply a multi step sacchrification rest to achieve better fermentability. The genatinization of barley starch happens between 140ºF and 150ºF [Palmer, 2006]. This means that at the optimal temperature for beta-amylase not not all starch may have gelatenized and is accessible to the enzymes. A multi step saccrification rest would employ a first rest between 140ºF and 150ºF which gives the beta amylase plenty of time to produce maltose from the accessible starches. Due to the limit dextrinase and already existing alpha amylase activity, the 1-6 links of amylopectin don't pose a limit for the beta amylase. This rest is commonly known as maltase rest. The lower the temperature of this rest, the longer the beta amylase will last and the more maltose is produced which increases the fermentability. Since the mash is generally not completely converted after the 30-60 min maltose rest, a second conversion rest, called saccrification or dextrinization rest is employed. This rest is held between 160ºF and 164ºF which is well above the gelatinization temperatuere for barley starch and within the optimal temperature range for alpha Amylase which will quickly convert the remaining starches. This rest is usually held until conversion of the mash is complete. An other benefit of this rest is the formation of foam positive glyco proteins [Fix, 1999]