How to Tell When an Apple Is Ripe — Apelil — Apples as a food product: varieties by sugar and

Two home tests replace guesswork: a thumb-press on the flesh and an iodine stain on a cut face.

The squeeze test: press the flesh near the stem with your thumb. Ripe flesh yields slightly and springs back; stony-hard means underripe, and a dent that stays means the apple is past its best.

The starch-iodine check: cut the apple across its equator and brush iodine on the cut face. Starch stains blue-black while sugary areas stay pale — mostly dark means wait, mostly clear means ripe.

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Professionals use the same ideas with instruments. A penetrometer reads flesh firmness, and most dessert apples are harvested at 14-18 lb (6.4-8.2 kg).

Sugar readings tell the same story from the other side: at harvest Granny Smith reads 12-14 °Bx, Honeycrisp 12-15 °Bx and Fuji 14-18 °Bx.

One test that does not work: floating. About 25 % of an apple's volume is air, so nearly all apples float — it says nothing about ripeness. Once an apple passes the tests, store it at 0-4 °C as described at /storing-apples, and pick the right variety for the job at /apple-varieties.

Wash and dry the apple, then cut it across the equator.
Brush the cut face with iodine tincture.
Wait a moment for the stain to develop.
Mostly blue-black: starchy, leave it longer. Mostly pale: sugars converted, ready to eat or store.