Hollow-Staff Plunger Churn: A Plunger in a Perforated Inner Cylinder Draws Air Down Its Staff on the Up Stroke

"On the descent of the dasher said valve closes, and such admitted fresh air is forcibly made to permeate the body of milk and to abruptly counteract its tendency to fill the partial void below the dasher."

Use a 20-litre food-grade bucket as the tub A and cut a 12 mm HDPE lid to it with a 24 mm hole in the middle. Cut a strip of 1 mm stainless sheet 320 mm wide and 645 long, drill twelve rows of 6 mm holes along it 25 mm apart, 36 to a row, the rows staggered, and roll it into a cylinder B 200 mm across, riveting the lap.

Cut a 22 mm stainless tube with a 19 mm bore 600 mm long as the hollow staff D. Glue the plunger on it 25 mm above its foot with silicone and pin it, and glue the valve seat to its foot. Cut a 30 mm disc of 2 mm natural rubber sheet as the valve b and fix it under the seat by one edge with a small stainless pin, so it hangs open when pulled down and lies shut when pushed up. Turn a hardwood T handle 240 mm long and fit it on the staff's top, leaving the tube's mouth open.

Stand the cylinder on its feet in the bucket and pour about 12 litres of heavy cream at about 15 °C, checked with the thermometer, into it; it runs out through the holes to fill the bucket. Put the plunger in, the lid over the staff, and work it up and down briskly, timing it. When the butter comes, lift out the plunger and the cylinder, then give the cream a few gentle strokes with the plunger to gather the butter. Take it out, pour the buttermilk into a bowl, wash the butter in cold water until it runs clear, salt and weigh it.

**William Hamilton** of St. Catharine, Linn County, Missouri, US 31,715, 19 March 1861, "Churn". He claimed, in a plunger churn with a hollow staff and air valve and the dasher's cylinder inside a tub with a milk space between, "a reticulated dasher cylinder or inner case so perforated as that a constant communication is established through the meshes of the inner cylinder between the inner and outer cylinders both above and below the dasher". He wrote that three to five minutes suffice and good cream makes butter in two; we have not tested that. He left the valve's form open ("any suitable valve"); ours is a rubber flap. The patent gives no sizes; every size here is ours.