(128. In other words, frying doughnuts using doughnut power is entirely self-sustainable.)
EDIT: I redid the math, and the number of doughnuts that you can fry is closer to, 160. 160 dozen, that is. My calculations had been going off of the assumption that the oil was to be heated from a temperature of zero degrees, which is of course inaccurate.
Here’s my logic (and you see what I mean when I say this project has a load of typography):
There is a simple mathematical formula to determine how many kilowatt hours it takes to heat any given body of oil to any given temperature in any given time. It goes:
Gallons × Temperature Rise (°F)
/
860 × Heat-up time (hrs.)
Oil tends to have a 15 minute reheat time, to the temperature of 375° F at which doughnuts are ideally cooked. Let’s say we’ve got a 50-pound capacity fryer- 6 gallons. Heating up to 375° from a room temperature of 70° F takes 1830/215 =~8.512 kilowatt hours to heat that much oil in 15 minutes and cook the first batch of doughnuts. Doughnuts absorb up to 30% of the oil you cook them in (so 15 grams per doughnut; in 6 gallons of oil that’s 2.5 grams per gallon, which is .7th of a percent oil per batch that gets absorbed assuming a batch size of 64 doughnuts (see below.)) The readdition of room-temp oil over subsequent batches is negligible but the addition of one part room temperature doughnut to 6 parts oil is going to bring down the batch of oil 1/7th (or 14%) of the way from 375° to 70°, or 43.57°, which we’ll round up to 44° assuming the addition of that .7% oil lost due to absorption each batch. 6 gallons multiplied by a temperature rise of 44°, and a 15 minute (.25 hour) reheat time, means that it’s going to take 1.228 kwh to reheat the oil to proper re-doughnut-cooking temperatures.
A batch of 100 doughnuts has, according to Google’s estimate of a typical doughnut (going based off the low end of the scale*) and converting from kilocalories to kilowatt hours, 22.315 kilowatt hours in it- turning the fryer on with a 15 minute heatup time to get to 375° (which is about right, though some commercial fryers can get it done in two thirds of the time,) followed by reheating it subsequently over succeeding batches, means you can get a little over 12 batches of doughnuts from the kwh of the kilocaloric energy of 100 doughnuts, from room temperature. If you started off with the fryer already on at 375° f, 22.315 / 1.228 means that you can get 18 batches out of it. And that’s at the low end of the doughnut calorie estimation scale!
How much is 12-18 doughnut batches?
8 twin-sized fry baskets can fit into a 50-pound fryer- 3 each on the side fry pots, 2 in the middle; each fry basket (17 1/2" x 9 1/8" x 6") can hold 8 doughnuts, so each batch contains 64 doughnuts.**768 doughnuts are in 12 batches, 1,152 doughnuts are in 18 batches- between the two batches are 160 dozen doughnuts. 150 dozen doughnuts a day is about average bakery output, so with 120 doughnuts left over there’s enough to take home twenty for yourself, and use the remaining hundred to power the fryer for the next day’s bake.
I've got illustrations and a list of sources for my claims in the project itself, which should be going up to you overmorrow, over at Pretzelize Me, Cap'n!.
*Different sites estimate the typical doughnut to have different numbers of calories; Wolfram Alpha gives us 22,509 kilocalories present in 100 doughnuts, while CalorieKing suggests it'd be closer to 24,108. I went with Google's estimation for the reasons stated above.
**The ideal ratio is one part of food to 6 parts of oil. The fry basket is 6 inches deep, submerged in oil deeper than that, about perfect for a doughnut one point five inches in height.
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