Final answer:
Pre-fermentation of the base material for grain vodka requires a grain malting process to activate enzymes that convert starches into fermentable sugars to which yeast is later added for fermentation.
Step-by-step explanation:
The pre-fermentation process for grain vodka typically requires a grain malting process. Grain malting activates enzymes within the grains that convert starches into sugars, which are then fermentable by yeast. Although pressure cooking with water can release starch, the conversion to fermentable sugars usually requires the malting step first. The addition of yeast comes after malting and mashing when the fermentable sugars are present, leading to fermentation. Thus, the correct answer would be 1) a grain malting process.