I'm making the Modernist Vichyssoise for dinner tomorrow night and I just started the first part of the recipe: I am confused about the use of the diastatic malt powder, however, so was hoping someone could enlighten me (chemistry was never a strong subject!).
The recipe has you simmer the potatoes until fully cooked, then drain them, add diastatic malt powder, and puree in a blender. You then put the puree in a water bath set to 52°C/126°F for 30 minutes, followed by moving them to a saucepan and heating to at least 75°C/167°F. From the book regarding that step: "This halts the enzymatic reatcions."
My concern is that at the time I added the malt powder my potatoes were just off the boil, so were very hot. I then pureed in a blender, which certainly didn't cool them down! I checked the temp before putting them in the bath and the puree was at 86°C/187°F. So it would appear that the water bath actually serves to cool the potatoes down to 52°C, and then you reheat them to 75°C. Does this seem plausible? How does the enzyme work that it is stopped on its return to 75°C, but works fine being put in so far above that?