Tempered-Air Bellows Churn: Bellows Blow Air Past a Can of Water and Up Through the Cream

"The bellows are then operated by working the lever G up and down, forcing the current of air created by them first through the reservoir C, where it is cooled or heated as needed, by coming in contact with the cooled or heated surface of the interior reservoir, and from thence through the air-pipe M, which distributes it through the milk or cream in the body of the churn."

Print the air chamber, two flap valves and the branch foot. Print in PETG at 0.2 mm layers, 30 % infill, 4 walls; wash before first use.

Glue a flap valve inside each inlet port of the chamber so it opens inward. Stand a clean tin can inside the chamber as the water reservoir and seal the chamber's lid round its rim with food-safe silicone. Glue a 20 mm food-grade pipe from the chamber's outlet, through the churn's lid, down to the branch foot near the bottom of a food-grade container.

Fix two hand bellows on the lid, one each side, their nozzles in the chamber's ports. Pivot a pine lever on a post between them and join it to each bellows' top board with a pine rod, so one bellows closes as the other opens.

US 17,439 drawing sheet, public domain (expired patent).

Let the heavy cream stand until it reaches about 15 °C, checked with the thermometer. Pour in 2 litres. Fill the can with cold water if the room is warm, or lukewarm if it is cold. Work the lever steadily so the air bubbles up through the cream; time until the butter comes. Pour off the buttermilk, add cold water, churn a little and pour off again until it runs clear; work in a pinch of salt and weigh the butter.

**Robert McCutcheon** of Towanda, Bradford County, Pennsylvania, US 17,439, 2 June 1857. He made the outer chamber of wood "for its non-conduction of heat" and the inner one of tin plate. He did not claim using air in a churn; he claimed the bellows, the two chambers and the air pipe arranged together. Bought bellows, a tin can, a container and printed parts stand in for his. FDM prints hold food in their layer lines, so wash well and replace when worn.