Coffee Percolator

Goodrich claims a base, an up-pipe, and a perforated basket of grounds, so that heating makes water circulate up the tube and shower the grounds "continuously." No pump — the heat is the pump.

Set a narrow copper tube upright in the middle of a clear heatproof vessel of water, its bottom near the base, its top above the water. You will watch the water climb it.

Sit a small perforated cup (a filter-lined basket) over the top of the tube so water leaving the tube falls onto it and drains through.

Put coffee grounds in the basket. They stay trapped up top, away from the water below — the drink never boils with loose grounds in it.

With an adult, heat the vessel gently. Watch the base: as it nears boiling, bubbles form in the tube.

Each bubble in the narrow tube pushes a slug of hot water up and out the top — a little fountain over the basket. This is the whole engine: a bubble pump.

The water ejected up top rains down through the grounds and drips back into the pot, carrying dissolved coffee with it. Round and round it goes.

Every pass pulls more coffee out of the grounds, so the water in the pot gets darker and stronger cycle by cycle. Note how the colour deepens.

Lift the tube out and heat again: the water just boils in place and nothing circulates. The narrow tube is what turns random boiling into a one-way pump. Put it back.

Too gentle and it never pumps; too fierce and it boils hard and turns bitter. A steady, gentle perk is best — the water should be hot, not roiling. This is why percolators are set to just tick over.

Pour a cup, and make another by boiling grounds loose and straining. The percolated cup is clear of grit and evenly strong; the boiled one is muddier. Note the difference the basket makes.

Because the same water passes the grounds again and again, a percolator can over-extract and turn harsh if left too long — the reason later drip and espresso methods pass water through once. Every design is a trade.

The patent. US 408,707, "Coffee-Pot", granted 13 August 1889 to Hanson Goodrich of Illinois. Goodrich's patent is the modern stovetop percolator: a base chamber, a central pump-tube, and a perforated basket, arranged so that ordinary boiling drives a continuous circulation. Earlier percolators existed (the idea goes back to the French in the early 1800s), but Goodrich's simple, self-contained arrangement is essentially the one that filled twentieth-century kitchens and campsites.

The physics is a bubble pump — a percolator has no moving parts. Heat the base and bubbles of steam form at the hottest spot. In the open pot a bubble just rises and pops, but a bubble caught in the narrow tube expands against the water above it and can only go one way — up — so it shoves a plug of hot water out the top of the tube (step 6). Bubble after bubble, the tube becomes a one-way pump lifting hot water from the base and raining it over the grounds (step 7), where it dissolves coffee and drips back to be pumped again (step 8). Remove the tube and the trick vanishes (step 9): the whole invention is the geometry of a narrow vertical channel over a heat source — the same principle as an airlift pump or a coffee-maker's siphon.

Where it sits. The percolator dominated home coffee until the 1970s, when automatic drip machines took over, because passing water through the grounds only once (rather than re-circulating it) avoids the bitter over-extraction a percolator risks (step 12). But the percolator survives on the stovetop and the campfire precisely because it needs nothing but a flame — no filter paper, no electricity, no moving parts. Your clear-jar model shows the entire idea: a tube, some heat, and a basket, brewing coffee by making boiling water pump itself.