Cream Filled Donut Day

What the day is

Cream Filled Donut Day is observed on September 14. A filled donut has no hole, for the obvious reason that the hole is where the filling goes.

Origin and background

The classic filling is pastry cream: milk, sugar, egg yolks and a starch, cooked until thick. It carries a rule that looks like superstition and is not. The mixture must be brought to a full boil for a short time, even though it has already thickened well before that point, because egg yolks contain an enzyme called alpha-amylase that digests starch. Leave it active and the cream will thicken beautifully in the pan and then go slack and soupy in the refrigerator hours later. Boiling denatures the enzyme and the set holds.

That egg content also determines how the donut has to be handled. Pastry cream is a low-acid, high-protein food and needs refrigeration, whereas a jelly-filled donut can sit on a counter all day because sugar and acid between them leave very little water available for bacteria. The two look like variations on one product and are not equivalent at all in this respect.

Many commercial cream fillings avoid the problem by not being custard. They are shortening, sugar and stabilizers whipped together, which is shelf-stable, pipes cleanly and does not weep, and the texture is the giveaway.

The donut underneath is the yeast-raised kind rather than the cake kind. Yeast dough is stretchy and builds an open interior that can be displaced by a filling nozzle, while cake donut batter is chemically leavened, tender and crumbly, and would tear.

Filling is done after frying and cooling, never before, since the filling would boil.

How to take part

• Boil pastry cream properly, or it will loosen overnight.
• Press a sheet against the surface as it cools to stop a skin forming.
• Refrigerate anything custard-filled, and do not do that with fried dough for long.
• Fill from the side, and stop when it gets heavy in your hand.