How microwave popcorn is made

Cure on the stalk

Growers leave the crop standing as long as they dare, weighing drier kernels against fall damp and toppling stalks. Machines now do almost all the picking.

Dry to popping moisture

Picked ears dry in ventilated cribs or with heated air until they hold 13.5 to 14 percent water. A cereal chemistry study found that the best level shifts a little with kernel size, and that missing it costs expansion.

13.5 to 14% moisture

Shell, screen and polish

At the plant the kernels come off the cob and ride over screens and separators that pull out broken pieces and debris. Polishing machines then rub away any clinging chaff.

Fold the empty bag

Tubular bag stock, usually paper plies around a microwave susceptor film, is cut to length and sealed at the bottom. The lower third folds up, so the charge will sit in the middle of the bag.

Drop in the kernels

A chain with clips carries each open bag upright to a filling station, where a device such as a dispensing wheel measures out the kernels.

Jet in the slurry

At the next station melted fat carrying very fine salt shoots down as a confined stream called a pencil jet. One patent's example gives about 35 grams in half a second. Coarse salt can plug that nozzle, so that patent drops it in at a third station.

Seal the top

Jaws close on the open end with heat or pressure and lock the charge inside. Heat or an adhesive holds the seal.

Fold and overwrap

A second fold gives the familiar three-folded packet. A moisture-barrier overwrap goes around it, and the wrapped bags are counted into cartons.