Potatoes are total starch.  So they must be broken down with an enzyme from either malted barley or hops. 

Potatoes

Today they are a staple food in many parts of the world and an integral part of much of the world’s food supply. As of 2014, potatoes were the world’s fourth-largest food crop after maize (corn), wheat, and rice. After a millennia of selective breeding, there are now over 5,000 different types of potatoes. It is an essential crop in Europe, especially Northern and Eastern Europe, where per capita production is still the highest in the world, while the most rapid expansion in production over the past few decades has occurred in southern and eastern Asia, with China and India leading the world in overall production as of 2018.

Potatoes are total starch.  So they must be broken down with an enzyme from either malted barley or hops. 

Sweet Potatoes

Sweet Potato contains within it alpha and beta amylase.  A regular potato has none.  It has the enzymes within it to covert the fermentable sugars into alcohol … Put a drop of iodine on a slice and you will see a very black spot indicating the potato is loaded with starch that will be converted to alcohol. 

149F is temp for 30 to 40 minutes to use up the beta amylase (middle portion).  Then raise temp to 155F for 2 hours for the alpha amylase (layer under the skin) to work its best.  Then to 170F to break down the potato material to mash it.