Twelve things from a kitchen shelf, each with the protein that does the work. Pick one: see the protein,
how sure AlphaFold's model of it is, one paragraph on how it works and one thing to try at the kitchen table.
Mechanism only: nothing here is advice about food, health or medicine.
the Sketcher's drawingPrediction Computed by a model, with how sure it is. Not an experiment.
Rennet
Why do a few drops of rennet set warm milk into a curd?
Rennet was first taken from a calf's stomach. Much rennet sold today is chymosin made by microbes from the calf gene (fermentation-produced chymosin), the same protein.
336 of 381 residues in ink (the model is sure: pLDDT 70 or more), 45 in pencil (less sure). Mean pLDDT 88.1 over 381 residues: very high 67%, confident 21%, low 6%, very low 6%. AlphaFold DB model v6 for UniProt P00794, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
Chymosin is a protein-cutting enzyme (a protease). In milk, casein proteins gather into tiny clusters called micelles, and one of them, κ-casein, forms a hairy outer layer that keeps the clusters apart. Chymosin cuts κ-casein at one bond near the middle of its chain. With the hairy layer cut away, the clusters stick together and the milk sets.
Try it in the kitchen
Warm a cup of milk until it feels just warm on your wrist. Stir in rennet as the packet says, then leave the cup still for half an hour. Tip it gently: the milk holds its shape. A second cup with no rennet stays runny.
Mechanism only: nothing here is advice about food, health or medicine.
Fresh pineapple
Why won't jelly set with fresh pineapple in it, when tinned pineapple is fine?
Fruit bromelain, from Ananas comosus ·
UniProt O23791 (found by protein name: UniProt gives it no gene name)
Fresh pineapple fruit holds fruit bromelain; the stem holds a related enzyme, stem bromelain. UniProt gives fruit bromelain no gene name, so it is found by its protein name and the pineapple taxon.
307 of 351 residues in ink (the model is sure: pLDDT 70 or more), 44 in pencil (less sure). Mean pLDDT 90.7 over 351 residues: very high 85%, confident 3%, low 1%, very low 11%. AlphaFold DB model v6 for UniProt O23791, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
Jelly sets because long gelatin chains tangle into a net as it cools. Fruit bromelain is a protease: it cuts gelatin chains into short pieces that cannot form a net, so the jelly stays runny. Tinned pineapple has been heated during canning, which unfolds the bromelain and stops it cutting.
Try it in the kitchen
Make two small cups of jelly from a packet, with a grown-up pouring the kettle. When the mix has cooled, add fresh pineapple pieces to one cup and tinned pineapple to the other. Chill both overnight and compare.
Mechanism only: nothing here is advice about food, health or medicine.
Meat tenderiser
What is the papaya in a meat-tenderiser powder?
Papain, from Carica papaya ·
UniProt P00784 (found by protein name: UniProt gives it no gene name)
Some meat tenderisers list papain, from the latex of unripe papaya. UniProt gives papain no gene name, so it is found by its protein name and the papaya taxon.
297 of 345 residues in ink (the model is sure: pLDDT 70 or more), 48 in pencil (less sure). Mean pLDDT 90.2 over 345 residues: very high 84%, confident 2%, low 7%, very low 7%. AlphaFold DB model v6 for UniProt P00784, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
Papain is a protease. On the surface of meat it cuts muscle proteins and connective tissue into smaller pieces, so the surface softens. It only works where the powder touches.
Try it in the kitchen
Use the jelly test: make two cups of jelly mix and let them cool. Stir a pinch of tenderiser that lists papain into one. Chill both overnight: the papain cup stays runnier.
Ovalbumin is the main protein of hen egg white, more than half of its protein.
359 of 386 residues in ink (the model is sure: pLDDT 70 or more), 27 in pencil (less sure). Mean pLDDT 92.1 over 386 residues: very high 82%, confident 11%, low 5%, very low 2%. AlphaFold DB model v6 for UniProt P01012, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
In raw egg white each ovalbumin chain is folded up and the white is clear. Heat jostles the chains open (they unfold, or denature), and the open chains stick to one another into a tangled net. The net scatters light, so the white turns opaque and firm. Cooling does not fold them back.
Try it in the kitchen
Put a spoonful of raw egg white in a cup and have a grown-up pour freshly boiled kettle water over it. It clouds and sets. Leave it to cool: it stays white.
16 of 190 residues in ink (the model is sure: pLDDT 70 or more), 174 in pencil (less sure). Mean pLDDT 53.4 over 190 residues: very high 2%, confident 6%, low 46%, very low 45%. AlphaFold DB model v6 for UniProt P02668, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
κ-casein sits on the outside of milk's casein clusters (micelles), and its loose, charged tail sticks out into the milk, so the clusters push one another apart. Acid from lemon juice cancels much of that charge, so the clusters stop pushing apart and clump into curds.
Try it in the kitchen
Stir a tablespoon of lemon juice into a cup of warm milk and leave it for five minutes: soft curds form. A cup with no lemon stays smooth.
Mechanism only: nothing here is advice about food, health or medicine.
A lactase tablet
What is the protein in a lactase tablet, and what does it cut?
Beta-galactosidase A, from Aspergillus oryzae (strain ATCC 42149 / RIB 40) ·
UniProt Q2UCU3
Many lactase tablets and drops are made with a β-galactosidase from a mould such as Aspergillus oryzae: a fungal protein, not the human lactase made in our gut. The label names the source. The reviewed UniProt entry is from one lab strain of the mould (RIB 40).
964 of 1005 residues in ink (the model is sure: pLDDT 70 or more), 41 in pencil (less sure). Mean pLDDT 95.4 over 1005 residues: very high 94%, confident 2%, low 1%, very low 3%. AlphaFold DB model v6 for UniProt Q2UCU3, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
β-galactosidase cuts lactose, the sugar in milk, into two smaller sugars, glucose and galactose. Lactose-free milk is made by adding a lactase enzyme to milk.
Try it in the kitchen
Taste a sip of ordinary milk and a sip of lactose-free milk side by side. The lactose-free milk tastes sweeter: glucose and galactose taste sweeter than the lactose they came from.
Mechanism only: nothing here is advice about food, health or medicine.
Biological washing powder
Why does biological washing powder lift egg and grass stains?
Subtilisin Carlsberg, from Bacillus licheniformis ·
UniProt P00780
Biological detergents carry proteases such as subtilisins, made by Bacillus bacteria. Subtilisin Carlsberg, from Bacillus licheniformis, is one of them.
340 of 379 residues in ink (the model is sure: pLDDT 70 or more), 39 in pencil (less sure). Mean pLDDT 91.2 over 379 residues: very high 86%, confident 3%, low 1%, very low 9%. AlphaFold DB model v6 for UniProt P00780, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
Stains such as egg, blood and grass hold proteins stuck to the cloth. Subtilisin cuts those proteins into small pieces that rinse away in the wash water.
Try it in the kitchen
Smear a little egg yolk on two cotton scraps and let them dry. Soak one in warm water with biological powder and one with non-biological powder for an hour, then rinse and compare. Wear gloves and keep the powder away from eyes.
Mechanism only: nothing here is advice about food, health or medicine.
A cut apple
Why does a cut apple turn brown, and why does lemon juice slow it?
Polyphenol oxidase, chloroplastic, from Malus domestica ·
UniProt P43309 (found by protein name: UniProt gives it no gene name)
Apple polyphenol oxidase. UniProt gives the reviewed apple entry no gene name, so it is found by its protein name and the apple taxon.
482 of 593 residues in ink (the model is sure: pLDDT 70 or more), 111 in pencil (less sure). Mean pLDDT 85.9 over 593 residues: very high 74%, confident 7%, low 3%, very low 16%. AlphaFold DB model v6 for UniProt P43309, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
Cutting an apple breaks its cells, so polyphenol oxidase meets the apple's phenol molecules and oxygen from the air. The enzyme turns phenols into quinones, which link up into brown pigments. Lemon juice is acidic, which slows the enzyme, and its vitamin C turns quinones back before they brown.
Try it in the kitchen
Cut three slices of apple. Leave one bare, brush one with lemon juice and dip one in plain water. Look again after an hour.
Invertase from baker's yeast, Saccharomyces cerevisiae. The reviewed entry is from the lab strain S288c.
507 of 532 residues in ink (the model is sure: pLDDT 70 or more), 25 in pencil (less sure). Mean pLDDT 93.3 over 532 residues: very high 88%, confident 8%, low 1%, very low 4%. AlphaFold DB model v6 for UniProt P00724, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
Yeast cells make invertase, much of it outside the cell. It cuts table sugar (sucrose) into glucose and fructose. The yeast takes those in and ferments them, giving off carbon dioxide gas, which puffs up the dough.
Try it in the kitchen
Put a spoon of dried yeast and a spoon of sugar into a bottle of warm (not hot) water and stretch a balloon over the neck. Set a second bottle beside it with yeast but no sugar. After half an hour, compare the balloons.
Mechanism only: nothing here is advice about food, health or medicine.
Gelatin
What is gelatin, and why does a jelly melt and set again?
Collagen alpha-1(I) chain, from Bos taurus ·
UniProt P02453
Gelatin is collagen boiled out of animal skin and bone, mostly from pigs and cattle. This is the cattle chain.
296 of 1463 residues in ink (the model is sure: pLDDT 70 or more), 1167 in pencil (less sure). Mean pLDDT 52.9 over 1463 residues: very high 15%, confident 6%, low 12%, very low 68%. AlphaFold DB model v6 for UniProt P02453, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
In the animal, three collagen chains wind together into a triple helix. Making gelatin pulls the chains apart. As warm gelatin cools, short stretches of chains wind back into helices and join many chains into a net that holds water: the jelly. Warm it and the net comes apart again.
Try it in the kitchen
Put one cube of set jelly on a saucer in a warm room and one in the fridge. The warm cube softens first. Put it back in the fridge and it sets again: unlike cooked egg white, the gelatin net comes and goes.
Mechanism only: nothing here is advice about food, health or medicine.
Glucose syrup
How is starch turned into glucose syrup?
Alpha-amylase, from Bacillus licheniformis ·
UniProt P06278
A heat-tolerant α-amylase from Bacillus licheniformis is one of the enzymes used to cut starch in factories.
482 of 512 residues in ink (the model is sure: pLDDT 70 or more), 30 in pencil (less sure). Mean pLDDT 95.1 over 512 residues: very high 94%, confident 0%, low 0%, very low 6%. AlphaFold DB model v6 for UniProt P06278, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
Starch is long chains of glucose. At high temperature, α-amylase cuts the chains into shorter pieces; a second enzyme, glucoamylase, then trims those pieces down to glucose.
Try it in the kitchen
Chew a plain cracker for a minute: it starts to taste sweet. The α-amylase in your own spit makes the same first cut.
Mechanism only: nothing here is advice about food, health or medicine.
Fresh kiwi fruit
Why does fresh kiwi fruit also stop jelly setting?
Actinidain, from Actinidia deliciosa ·
UniProt A5HII1 (found by protein name: UniProt gives it no gene name)
Actinidin (actinidain) from green kiwi fruit. UniProt gives it no gene name, so it is found by its protein name and the kiwi taxon.
316 of 380 residues in ink (the model is sure: pLDDT 70 or more), 64 in pencil (less sure). Mean pLDDT 88.4 over 380 residues: very high 75%, confident 8%, low 11%, very low 6%. AlphaFold DB model v6 for UniProt A5HII1, from Fold Commons' snapshot of 2026-10-08. A prediction, not an experiment.
How it works
Actinidin is a protease of the same family as papain and bromelain. Like them, it cuts gelatin chains into pieces too short to form a net.
Try it in the kitchen
Make two cups of jelly mix and let them cool. Add fresh kiwi pieces to one and apple pieces to the other. Chill both overnight and compare.
Mechanism only: nothing here is advice about food, health or medicine.
How this shelf is made
Each item names a gene and an organism (or, where UniProt gives the reviewed entry no gene name, its exact protein
name and organism). The accession, organism and protein name are looked up in UniProt's reviewed entries; an item
with no single reviewed match, or no AlphaFold DB model, is left off the shelf rather than guessed. Ink and pencil
and the confidence words are computed from the model's own per-residue confidence (pLDDT). Each model is one chain
on its own: the milk, the cell, the water and the other molecules it meets are not in the picture.