Edible Chemistry Experiments

Chemistry experiments you can eat - from meringue to spherification

Edible Chemistry: Experiments You Can Eat

Food is chemistry you can taste. This guide covers experiments that demonstrate chemical principles through cooking and food science - and you get to eat the results.

Safety Notes

Use food-grade ingredients only
Follow food safety practices (clean hands, surfaces, proper temperatures)
Be aware of allergies
Adult supervision required for heat and sharp tools
Some experiments involve hot sugar - use extreme caution (burns severely)

Protein Chemistry

Meringue: Foam Stabilization

Difficulty: Easy | Time: 30 minutes

Egg whites transform from liquid to solid foam through mechanical action and protein denaturation.

Materials: - 3 egg whites (room temperature) - 150g sugar - Pinch of cream of tartar or lemon juice - Electric mixer

Procedure: 1. Ensure bowl and beaters are completely grease-free (fat destabilizes foam) 2. Beat egg whites on medium speed until foamy 3. Add cream of tartar 4. Increase speed, beat until soft peaks form 5. Gradually add sugar while beating 6. Continue until stiff, glossy peaks form 7. Bake at 100°C for 1-2 hours until crisp

The Science: - Proteins unfold: Beating denatures albumin proteins, exposing hydrophobic regions - Air incorporation: Unfolded proteins surround air bubbles, hydrophobic parts face inward - Acid stabilization: Cream of tartar (tartaric acid) lowers pH, strengthening protein bonds - Sugar stabilization: Sugar dissolves into protein film, adding viscosity and structure - Why no fat?: Fat molecules insert into protein films and destabilize them

Experiment variations: 1. Try without cream of tartar - notice less stability 2. Add a drop of oil - watch the foam collapse 3. Use cold vs. room temperature eggs - room temp whips faster 4. Add sugar early vs. late - early addition makes denser, chewier meringue

Cheese Making: Acid Coagulation

Difficulty: Easy | Time: 30 minutes

Make fresh paneer or ricotta by denaturing milk proteins with acid.

Materials: - 1 liter whole milk - 2-3 tablespoons lemon juice or white vinegar - Salt - Cheesecloth - Thermometer

Procedure: 1. Heat milk to 85-90°C (just below boiling) 2. Remove from heat 3. Add acid slowly while stirring gently 4. Curds (solid) separate from whey (liquid) within seconds 5. Let stand 10 minutes 6. Strain through cheesecloth 7. Rinse curds with cold water to remove acid taste 8. Squeeze out excess liquid 9. Add salt, press into shape

The Science: - Milk contains casein proteins suspended in water - Casein micelles have negative surface charges that repel each other - Acid (H\(^+\) ions) neutralizes these charges - Without repulsion, proteins clump together (coagulation) - Heat accelerates the process and denatures whey proteins too

Reaction: \[\ce{Casein^{-} + H+ -> Casein (precipitate)}\]

Variations: - Use rennet instead of acid for different texture (enzymatic coagulation) - Try different acids: lemon, vinegar, citric acid - taste differences! - Experiment with temperature: too low = no curds, too high = rubbery texture

Ceviche: Acid-Cooked Fish

Difficulty: Medium | Time: 2-4 hours (mostly waiting)

“Cook” fish using acid instead of heat - both denature proteins.

Materials: - 250g very fresh firm white fish (sea bass, halibut, snapper) - 150ml fresh lime juice (must be fresh) - 50ml fresh lemon juice - Salt - Diced onion, cilantro, chili (optional)

Procedure: 1. Cut fish into 1cm cubes 2. Place in glass bowl (not metal - reacts with acid) 3. Cover completely with citrus juice 4. Add salt 5. Refrigerate 2-4 hours, stirring occasionally 6. Fish turns opaque and firms up - it’s “cooked” 7. Drain most liquid, add aromatics, serve immediately

The Science: - Citric acid denatures fish proteins (breaks hydrogen bonds) - Proteins unfold and rebond in new configurations - Texture changes from translucent/soft to opaque/firm - Same structural change as heat denaturation, different mechanism - pH must drop below 4 for effective denaturation

Important: Use sushi-grade fish - acid doesn’t kill parasites like heat does!

Sugar Chemistry

Honeycomb Candy: Thermal Decomposition

Difficulty: Medium | Time: 20 minutes

Hot sugar + baking soda = explosive foam that hardens into crunchy candy.

Materials: - 200g sugar - 5 tablespoons golden syrup or corn syrup - 1 tablespoon baking soda (sodium bicarbonate) - Heavy-bottomed pot - Candy thermometer - Greased baking tray

Procedure: 1. Combine sugar and syrup in pot 2. Heat over medium, stirring until sugar dissolves 3. Stop stirring, let boil until 150°C (hard crack stage) 4. Remove from heat immediately 5. Quickly whisk in baking soda 6. Mixture foams up dramatically (5-6× volume) 7. Pour immediately onto greased tray - don’t spread! 8. Let cool completely, break into pieces

The Science: \[\ce{2 NaHCO3 ->[\Delta] Na2CO3 + H2O + CO2 ^}\]

Baking soda decomposes at high temperature, releasing CO\(_2\) gas
Hot sugar is viscous enough to trap gas bubbles
As sugar cools and hardens, bubbles are frozen in place
Result: aerated glass-like structure (like frozen foam)

Caution: Molten sugar is extremely hot (150°C+) and causes severe burns. Keep children away during cooking.

Variations: - Dip in chocolate (like Crunchie bars) - Add a pinch of citric acid for tangier flavor

Caramel vs. Maillard: Two Types of Browning

Difficulty: Easy | Time: 15 minutes each

Two different chemical reactions both create brown colors and complex flavors.

Caramelization (Sugar Only)

Materials: - 100g white sugar - 2 tablespoons water - Heavy pot

Procedure: 1. Dissolve sugar in water over medium heat 2. Stop stirring once dissolved 3. Watch color progression: - 160°C: Light gold - 170°C: Amber - 180°C: Dark caramel - 190°C+: Bitter/burnt 4. Remove from heat, carefully add cream or butter for caramel sauce

The Science: - Pure thermal decomposition of sucrose - Sucrose breaks into glucose and fructose - These react and polymerize into hundreds of compounds - Brown polymers (caramelans, caramelens, caramelins) form - Flavor compounds: diacetyl (buttery), furans (nutty), maltol (toasty)

Maillard Reaction (Sugar + Protein)

Materials: - Bread - Butter - Toaster or pan

Procedure: 1. Toast bread until golden brown 2. Observe: browning starts where butter was applied 3. Compare toasted vs. untoasted flavor

The Science: - Amino acids react with reducing sugars - Requires both protein AND sugar present - Produces melanoidins (brown pigments) - Creates thousands of flavor compounds - This is why seared meat, baked bread, and roasted coffee taste complex

Key difference: - Caramelization: sugar alone, higher temperature (160°C+) - Maillard: sugar + protein, lower temperature (110°C+)

Experiment: Compare plain sugar syrup heated to caramel vs. milk (lactose + casein) heated to dulce de leche. Both brown, but flavors are completely different!

Rock Candy: Supersaturation and Crystal Growth

Difficulty: Easy | Time: 1-2 weeks

Grow large sugar crystals from supersaturated solution.

Materials: - 3 cups sugar - 1 cup water - Wooden skewers or string - Tall glass jars - Food coloring (optional) - Clothespins

Procedure: 1. Boil water, gradually dissolve sugar until no more dissolves 2. Add food coloring if desired 3. Let cool slightly (5 minutes) 4. Wet skewer, roll in sugar (seed crystals) 5. Let dry completely 6. Pour syrup into jars 7. Suspend skewers using clothespins, not touching sides or bottom 8. Cover loosely, place in undisturbed location 9. Crystals grow over 1-2 weeks 10. Remove, let dry, enjoy!

The Science: - Hot water dissolves more sugar than cold (increased solubility) - Cooling creates supersaturated solution (more dissolved than should be possible) - System is unstable - sugar wants to crystallize out - Seed crystals provide nucleation sites - Slow cooling = larger crystals; fast cooling = many small crystals

Troubleshooting: - Crystals on jar not stick? Solution wasn’t saturated enough - Cloudy/grainy? Cooled too fast, add more sugar and reheat - Nothing happening? Wait longer, or solution cooled before supersaturating

Starch Gelatinization: Thickening a Sauce

Difficulty: Very Easy | Time: 15 minutes

Watch starch granules absorb water and transform a liquid into a thick gel.

Materials: - 2 tablespoons cornstarch (or arrowroot, or plain flour) - 250ml cold water or stock - Small pot - Stirring spoon

Procedure: 1. Whisk cornstarch into cold liquid until fully dissolved (no lumps). 2. Place over medium heat and stir constantly. 3. At around 60–70°C, the liquid suddenly thickens — stir quickly to keep smooth. 4. Continue to boil for 1 minute (this “cooks out” the starchy taste). 5. Remove from heat. The sauce continues to thicken as it cools.

Compare: - Cornstarch: Very clear, glossy gel. Thinned by prolonged boiling or acids. - Arrowroot: Similar clarity, but breaks down if overcooked or frozen. - Flour roux: Opaque, nutty flavor from Maillard reaction with fat. More forgiving.

The Science: Starch granules are tightly packed structures of amylose and amylopectin. In cold water they are insoluble. When heated, water penetrates, the granules swell enormously (up to 100×), and amylose leaches out. The swollen granules and loose amylose chains form a tangled network that immobilizes the liquid — a gel.

The mixture must be stirred constantly during heating because swelling granules can clump together, forming lumps that are impossible to dissolve.

Experiment: Make three identical sauces. Leave one plain. Add 1 tablespoon of lemon juice to the second. Freeze and thaw the third. Compare consistency. (Acid and freeze-thaw both break down the starch gel.)

Mayonnaise: Emulsion Formation

Difficulty: Medium | Time: 15 minutes

Create a stable emulsion of oil in water using egg yolk as emulsifier.

Materials: - 1 egg yolk (room temperature) - 1 tablespoon lemon juice or vinegar - 1 teaspoon mustard - 200ml neutral oil - Salt - Whisk or immersion blender

Procedure: 1. Combine yolk, acid, mustard, and salt in bowl 2. Whisk thoroughly 3. Add oil DROP BY DROP while whisking constantly 4. After ~50ml, can add oil in thin stream 5. Continue until thick and creamy 6. Taste and adjust seasoning

The Science: - Oil and water don’t mix (immiscible) - Lecithin in egg yolk is an emulsifier - Emulsifier molecules have hydrophilic (water-loving) and hydrophobic (oil-loving) ends - They surround tiny oil droplets, hydrophobic end in oil, hydrophilic end in water - This prevents droplets from merging (coalescence) - Mustard adds additional emulsifiers and flavor

Why it can break: - Adding oil too fast: droplets too large to stabilize - Cold ingredients: lecithin less effective - Too much oil: not enough emulsifier

Recovery: If broken (separated, curdled), start new yolk in clean bowl, slowly whisk in broken mayo.

Experiment: Try making mayo without mustard, then with. Notice stability difference.

Butter: Breaking an Emulsion

Difficulty: Very Easy | Time: 15-20 minutes

Cream is an emulsion - mechanical action breaks it into butter (fat) and buttermilk (water).

Materials: - 500ml heavy cream (high fat content, not ultra-pasteurized if possible) - Jar with tight lid, or stand mixer - Cold water - Salt (optional)

Procedure: 1. Pour cream into jar (fill halfway) or mixer bowl 2. Shake vigorously (jar) or beat on high (mixer) 3. Cream thickens to whipped cream (3-5 min) 4. Continue - suddenly separates into butter clumps and liquid (5-10 min) 5. Pour off buttermilk (save for baking!) 6. Rinse butter in cold water, kneading until water runs clear 7. Knead in salt if desired 8. Press out remaining water, shape

The Science: - Cream is fat droplets suspended in water (emulsion) - Fat globules are protected by membrane proteins - Agitation damages membranes - Exposed fat sticks together - Eventually fat clumps large enough to separate from water phase - Temperature matters: too cold = hard to break membranes, too warm = fat melts

Experiment: Try different cream temperatures (cold from fridge vs. room temp). Notice how long each takes and final texture.

Vinaigrette: Temporary Emulsion

Difficulty: Very Easy | Time: 5 minutes

Unlike mayo, a simple vinaigrette separates - demonstrating unstable emulsions.

Materials: - 3 tablespoons olive oil - 1 tablespoon vinegar - 1/2 teaspoon mustard - Salt, pepper - Jar

Procedure: 1. Combine all ingredients in jar 2. Shake vigorously - becomes cloudy/creamy 3. Time how long until separation begins 4. Try again with vs. without mustard - compare separation times

The Science: - Without strong emulsifier, oil droplets merge quickly - Mustard contains mucilage that slows separation but can’t prevent it - This is a temporary or unstable emulsion - Contrast with mayo: enough emulsifier for permanent stability

Gel Chemistry

Fruit Juice Gummies: Gelatin Gels

Difficulty: Easy | Time: 30 min + 2 hours setting

Transform liquid into solid using protein-based gelation.

Materials: - 200ml fruit juice (not pineapple, kiwi, or papaya!) - 2 tablespoons (14g) unflavored gelatin - 2 tablespoons sugar (optional) - Silicone molds

Procedure: 1. Pour 50ml cold juice in bowl 2. Sprinkle gelatin over surface, let bloom 5 minutes 3. Heat remaining juice until steaming (not boiling) 4. Add sugar if using, stir to dissolve 5. Pour hot juice over bloomed gelatin, stir until dissolved 6. Pour into molds 7. Refrigerate 2+ hours until firm

The Science: - Gelatin is collagen protein extracted from animal bones/skin - In hot water, proteins are random coils (sol state) - Cooling allows triple-helix structures to form (gel state) - Helices create 3D network trapping water - Process is reversible: heating returns to liquid

Why not pineapple/kiwi/papaya? These contain proteases (bromelain, actinidin, papain) that digest gelatin proteins, preventing gel formation. Test it - make one batch with canned pineapple (enzyme destroyed by heat) and one with fresh. Fresh won’t set!

Agar Fruit Jellies: Polysaccharide Gels

Difficulty: Easy | Time: 30 min + 1 hour setting

Vegetarian alternative using seaweed-derived agar.

Materials: - 250ml fruit juice or flavored liquid - 2g agar powder (or 8g agar flakes) - Sugar to taste

Procedure: 1. Whisk agar into cold liquid 2. Bring to boil, stirring constantly 3. Boil 2 minutes (agar must fully dissolve) 4. Pour into molds 5. Sets at room temperature in 1 hour 6. Refrigerate for firmer texture

The Science: - Agar is a polysaccharide from red algae - Forms gels at much lower concentrations than gelatin - Sets at ~35°C, melts at ~85°C (large hysteresis) - Gel structure: double helices of agarose aggregate into bundles - Unlike gelatin, agar gels don’t melt in your mouth - different texture

Comparison Experiment: Make identical jellies with gelatin vs. agar. Compare: - Setting time - Texture when eaten - What happens left at room temperature - Resistance to pineapple juice

Jam Making: Pectin Gels

Difficulty: Medium | Time: 1 hour

Pectin from fruit creates gels only under specific conditions.

Materials: - 500g fruit (strawberries, raspberries, or other) - 400g sugar - 2 tablespoons lemon juice - Pectin (if using low-pectin fruit)

Procedure: 1. Crush fruit in heavy pot 2. Add sugar and lemon juice 3. Heat slowly until sugar dissolves 4. Boil rapidly until setting point (~105°C) 5. Test: drop on cold plate, push with finger - should wrinkle 6. Pour into sterilized jars

The Science: Pectin gels require THREE conditions: 1. Pectin: Polysaccharide from plant cell walls 2. Sugar (60-65%): Dehydrates pectin, allows bonding 3. Acid (pH 2.8-3.5): Neutralizes pectin’s negative charges

Without enough of any component, gel fails: - Low sugar = runny jam - Low acid = won’t set (add lemon juice!) - Low pectin = add commercial pectin or use high-pectin fruit

High-pectin fruits: Apples, citrus, quince, gooseberries Low-pectin fruits: Strawberries, peaches, cherries (need added pectin)

Gas Production

Bread: Yeast Fermentation and Gluten

Difficulty: Medium | Time: 3-4 hours

Bread combines gas production (leavening) with protein structure (gluten network).

Materials: - 500g bread flour - 7g instant yeast - 10g salt - 325ml warm water - Olive oil

Procedure: 1. Mix flour, yeast, salt 2. Add water, mix until shaggy dough 3. Knead 10 minutes until smooth and elastic 4. Oil bowl, place dough, cover 5. Let rise until doubled (1-2 hours) 6. Punch down, shape, let rise again (1 hour) 7. Bake at 220°C for 30-40 minutes

The Science:

Yeast fermentation: \[\ce{C6H12O6 -> 2 C2H5OH + 2 CO2}\] Yeast converts sugars to alcohol and CO\(_2\). Gas creates bubbles; alcohol evaporates during baking.

Gluten development: - Flour contains glutenin and gliadin proteins - Water + mechanical work = gluten network - Gluten is elastic (stretches) and plastic (holds shape) - Network traps CO\(_2\) bubbles, allowing rise

Experiment: Make two doughs - knead one for 10 min, one for 2 min. Compare rise and final texture. Under-kneaded = dense, tears easily.

Quick Bread: Chemical Leavening

Difficulty: Easy | Time: 45 minutes

Baking soda + acid = instant CO\(_2\), no waiting for yeast.

Materials: - 200g flour - 1.5 teaspoons baking powder (or 1/2 tsp baking soda + acid) - 50g sugar - 1/4 teaspoon salt - 180ml buttermilk (acidic) - 1 egg - 60g melted butter

Procedure: 1. Mix dry ingredients 2. Whisk wet ingredients separately 3. Combine wet into dry, mix just until combined (don’t overmix!) 4. Pour into greased loaf pan 5. Bake immediately at 180°C for 35-40 minutes

The Science:

Baking soda (sodium bicarbonate): \[\ce{NaHCO3 + H+ -> Na+ + H2O + CO2}\] Requires acid to react. Acid sources: buttermilk, yogurt, lemon, brown sugar, cocoa.

Baking powder = baking soda + dry acid (cream of tartar or sodium aluminum sulfate) - “Double-acting”: reacts once when wet, again when heated - Self-contained, doesn’t need acidic ingredients

Why not overmix? Mixing develops gluten. For tender quick breads, you want minimal gluten = minimal mixing.

Popcorn: Steam Explosion

Difficulty: Very Easy | Time: 5 minutes

Water trapped inside kernel becomes steam, causing explosive expansion.

Materials: - Popcorn kernels - Oil - Covered pot or air popper - Salt

Procedure: 1. Heat oil in pot over medium-high 2. Add kernels in single layer 3. Cover, shake occasionally 4. Kernels pop when steam pressure exceeds hull strength 5. Remove when popping slows to 2-3 seconds between pops 6. Season immediately (salt sticks to hot oil)

The Science: - Each kernel contains 13-14% moisture - Hard hull (pericarp) seals in water - Heating converts water to steam - At ~180°C, pressure reaches ~135 psi (9 bar) - Hull ruptures, starch expands rapidly (up to 50× volume) - Starch cools instantly into foam structure

Experiment: Dry out kernels in oven (100°C, 1 hour) before popping. Many won’t pop - insufficient moisture!

Why old kernels don’t pop: Moisture has escaped through micro-cracks in hull.

Casein Plastic: Protein Polymerization

Difficulty: Easy | Time: 30 minutes + drying time

Turn milk into a moldable solid — the same material used for early 20th-century buttons, buckles, and billiard balls.

Materials: - 250ml whole milk - 3-4 tablespoons white vinegar - Small pot - Cheesecloth or paper towels - Food-grade molds (optional)

Procedure: 1. Heat milk to just below boiling (85°C), stirring occasionally. 2. Remove from heat. Add vinegar a tablespoon at a time, stirring. 3. Curds form immediately and clump together — same as cheese making. 4. Let cool 5 minutes, then strain through cheesecloth. 5. Squeeze out as much liquid as possible. 6. While still warm and pliable, knead for a few minutes. 7. Mold into any shape — roll flat, press into a mold, or sculpt. 8. Leave to harden for 24–48 hours. The plastic becomes firm and can be sanded or painted.

The Science: Vinegar lowers the pH until casein proteins reach their isoelectric point (~pH 4.6), where their net charge is zero and they aggregate. The compressed, dehydrated casein forms a continuous polymer network — a simple bioplastic. When heated, the chains are still mobile enough to shape; cooling locks them in place.

This material is called Galalith (Greek: milk stone) commercially, patented in 1897. It was widely used before petroleum-based plastics took over in the 1940s.

Experiment: Compare plasticity at different temperatures — warm curds mold easily, cold curds crumble. What does this tell you about the polymer network?

Color-Changing Drinks: Butterfly Pea Flower

Difficulty: Very Easy | Time: 10 minutes

Create drinks that change color when acid is added.

Materials: - Dried butterfly pea flowers (available online or at Asian markets) - Hot water - Lemon or lime juice - Sparkling water - Sugar or simple syrup

Procedure: 1. Steep 5-6 flowers in 250ml hot water for 5 minutes 2. Strain - you have deep blue tea 3. Add sugar if desired 4. Pour over ice 5. Add citrus juice - watch it transform to purple/pink! 6. Stir - color changes throughout drink

The Science: - Butterfly pea contains anthocyanins (see natural-indicators.qmd) - Blue at neutral pH - Acid shifts equilibrium to flavylium cation form (purple/pink) - Great for cocktails: start blue, add lime, becomes purple

Variations: - Layer carefully: blue tea on bottom, clear lemonade on top, watch colors mix - Add baking soda to turn it green - Make gradient drinks with different acidity levels

Turmeric pH Indicator

Difficulty: Very Easy | Time: 15 minutes

Turmeric changes from yellow to vivid red-pink in strongly basic conditions — make kitchen indicator paper.

Materials: - Ground turmeric — 1 teaspoon - Rubbing alcohol (or vodka) — 50ml - White paper or coffee filters - Household test substances: baking soda solution, vinegar, soap, lemon juice, antacid tablet

Procedure:

Make turmeric paper: 1. Stir turmeric into alcohol until dissolved (deep yellow). 2. Dip strips of paper into the solution, let soak 30 seconds. 3. Hang to dry — paper turns yellow-orange.

Testing: 4. Drop different household liquids onto separate strips. 5. Baking soda or soap (basic): strip turns bright pink/red almost instantly. 6. Vinegar or lemon juice (acidic): strip stays yellow. 7. Let dry — the red color may shift or fade depending on pH.

The Science: The active molecule in turmeric is curcumin, a natural pigment. Like other pH indicators, its color depends on whether it has donated or accepted a proton. In acidic and neutral conditions curcumin is yellow; in strongly basic conditions (pH > 8), it converts to a red-pink form. The transition is particularly striking because the red is so vivid against the yellow.

Turmeric is less precise than universal indicator — it doesn’t distinguish between mildly and strongly acidic, just between “not basic” and “basic.” But the strong base color change is one of the most dramatic of any kitchen indicator.

Warning: Turmeric stains everything it touches permanently. Use paper you don’t mind discarding and protect work surfaces.

Self-Inflating Balloon (Edible Version)

Difficulty: Very Easy | Time: 10 minutes

Demonstrate CO\(_2\) production with ingredients you can taste.

Materials: - Bottle - Balloon - 2 tablespoons baking soda - 100ml vinegar (or citric acid solution)

Procedure: 1. Put vinegar in bottle 2. Put baking soda in balloon 3. Stretch balloon over bottle opening 4. Tip balloon up - baking soda falls into vinegar 5. CO\(_2\) inflates balloon

Edible version: 1. Mix citric acid and baking soda (equal parts) in small dish 2. Taste a tiny bit - fizzes on tongue! 3. This is the basis of sherbet powder and fizzy candy

\[\ce{C6H8O7 + 3 NaHCO3 -> Na3C6H5O7 + 3 H2O + 3 CO2}\]

Antioxidants and Apple Browning

Difficulty: Very Easy | Time: 30 minutes

Find out which treatments best prevent enzymatic browning — and why.

Materials: - 2 apples - Vitamin C tablet (ascorbic acid) dissolved in 50ml water, or fresh lemon juice - Several small dishes - Saltwater (1 tsp salt in 100ml water) - Vinegar - Plain water - Optional: honey dissolved in water, commercial fruit preserver

Procedure: 1. Cut apple into identical slices and immediately place one in each dish: - Dry (control, nothing) - Plain cold water - Saltwater - Lemon juice or ascorbic acid solution - Vinegar - Honey solution 2. After 20–30 minutes, compare the browning on each slice. 3. Rank them from most to least browned.

The Science: Apple flesh contains phenolic compounds and an enzyme called polyphenol oxidase (PPO). When cells are damaged (by cutting), the enzyme contacts its substrates and oxidizes phenols into brown quinone pigments.

Ascorbic acid (vitamin C): Directly reduces quinones back to phenols, and also depletes dissolved oxygen. Very effective — the same reason it’s used commercially.
Acid (lemon, vinegar): Low pH inhibits PPO activity. Effective, but changes flavor.
Salt: Slightly inhibits PPO. Less effective than acid or vitamin C.
Honey: Contains trace PPO inhibitors, mild effect.
Plain water: Dilutes and partially excludes oxygen. Minimal effect.

Extension: Leave all slices for 2 hours. Which treatments hold out longest? Does vitamin C eventually run out?

Colloids and Non-Newtonian Fluids

Oobleck: Shear-Thickening Fluid

Difficulty: Very Easy | Time: 5 minutes

A mixture that flows like liquid when handled gently but acts like a solid under impact.

Materials: - 1 cup (about 120g) cornstarch - ~½ cup (100ml) water - Bowl - Food coloring (optional)

Procedure: 1. Pour cornstarch into bowl. 2. Add water slowly while mixing with your hands. Start with less water and add more until it barely comes together. 3. The ratio is roughly 2:1 cornstarch to water by volume. Too much water = runny; too little = crumbly. 4. Explore: - Hit the surface sharply with your fist — it feels solid. - Rest your hand gently on the surface — it sinks in slowly. - Try to grab a handful and squeeze — it feels solid. Release the pressure — it flows through your fingers. - Try stirring quickly vs. slowly.

The Science: Oobleck is a shear-thickening (dilatant) fluid — its viscosity increases with applied stress. The cornstarch particles form a dense suspension. Under gentle, slow forces the particles have time to rearrange and flow past each other. Under sudden, high forces there isn’t time to rearrange, so the particles jam together and the mixture behaves like a solid.

This is the opposite of many common substances: ketchup is shear-thinning — it flows more easily when shaken. Oobleck is shear-thickening.

Real-world application: liquid body armor research uses shear-thickening fluids because they are flexible during normal movement but stiffen on impact.

Experiment: Try varying the water ratio. Find the minimum water amount where it still flows at all. Does adding a pinch of salt change the behaviour?

Osmosis and Diffusion

Pickles: Osmotic Preservation

Difficulty: Easy | Time: 15 min + 24+ hours waiting

Salt draws water out of vegetables through osmosis.

Materials: - Cucumbers (small, pickling type) - Salt (non-iodized) - Water - Garlic, dill, spices - Glass jar

Procedure for quick pickles: 1. Dissolve 3 tablespoons salt in 500ml warm water 2. Pack cucumbers in jar with garlic, dill 3. Pour brine over cucumbers 4. Keep submerged (weight if needed) 5. Refrigerate 24-48 hours 6. Taste - crunchy, salty, tangy!

The Science: - High salt concentration outside cells - Water moves from low to high solute concentration (osmosis) - Cells lose water, vegetables soften slightly but stay crunchy - Salt inhibits bacterial growth - Over time, lactic acid bacteria produce tanginess (fermented pickles)

Experiment: Make pickles with different salt concentrations (2%, 5%, 10%). Compare texture and flavor.

Strawberry DNA Extraction

Difficulty: Easy | Time: 20 minutes

Extract visible DNA from fruit using kitchen ingredients.

Materials: - 2-3 strawberries - Dish soap - Salt - Ice-cold rubbing alcohol (isopropyl, 70%+) - Plastic bag - Coffee filter - Clear glass

Procedure: 1. Mash strawberries in bag until smooth 2. Add 1 tablespoon dish soap + 1/2 teaspoon salt + 2 tablespoons water 3. Mix gently for 1 minute 4. Filter through coffee filter into glass 5. Slowly pour cold alcohol down side of glass (layer on top) 6. Wait 2-3 minutes 7. White stringy material appears at interface - that’s DNA! 8. Spool it onto a toothpick

The Science: - Mashing breaks cell walls mechanically - Soap dissolves cell membranes (lipid bilayers) - Salt causes DNA to clump together (neutralizes phosphate charges) - DNA is insoluble in alcohol - precipitates out - Strawberries are octoploid (8 copies of genome) = lots of DNA

Note: While technically “edible,” the alcohol makes this more demonstration than snack!

Spherification (Expanded from experiments.qmd)

Basic Spherification: Juice Caviar

Difficulty: Medium | Time: 30 minutes

Create small spheres with liquid centers.

Materials: - 100ml fruit juice - 0.5g sodium alginate - 500ml water - 2.5g calcium chloride - Immersion blender - Syringes or squeeze bottles - Slotted spoon

Procedure: 1. Blend alginate into juice, let rest 15 min (removes bubbles) 2. Dissolve calcium chloride in water 3. Drip juice mixture into calcium bath 4. Spheres form instantly 5. Let sit 2 minutes for thicker skin 6. Remove with slotted spoon, rinse in water 7. Serve immediately

The Science: \[\ce{2 Na-Alginate + Ca^{2+} -> Ca-Alginate (gel) + 2 Na+}\]

Alginate (from seaweed) is a long-chain polysaccharide
Calcium ions cross-link alginate chains
Gel forms at interface where alginate meets calcium
Longer in bath = thicker membrane

Troubleshooting: - Tails on spheres: Lower slowly, don’t drop from height - Spheres don’t form: Juice too acidic (alginate needs pH > 3.5) - Flat spheres: Blend alginate better, let rest longer

Reverse Spherification: Large Spheres

Difficulty: Medium | Time: 45 minutes

Better for larger spheres and dairy-based liquids.

Materials: - 100ml cream or yogurt - 1g calcium lactate - 500ml water - 2.5g sodium alginate

Procedure: 1. Mix calcium lactate into cream 2. Blend alginate into water, rest 30 min 3. Carefully spoon cream mixture into alginate bath 4. Let set 3 minutes 5. Remove, rinse gently 6. Spheres can be stored in plain water

The Science: - Calcium is inside the sphere, alginate outside - Gel forms inward from surface - Sphere can be stored longer without gelling solid - Works with calcium-containing liquids (dairy, some juices)

Dehydration and Concentration

Fruit Leather: Moisture Removal

Difficulty: Easy | Time: 6-8 hours

Concentrate fruit by removing water.

Materials: - 500g ripe fruit - 2 tablespoons honey or sugar (optional) - Blender - Baking sheet - Parchment paper - Oven or dehydrator

Procedure: 1. Blend fruit until completely smooth 2. Add sweetener if desired 3. Spread thin layer (3mm) on parchment-lined sheet 4. Dry at 75°C for 6-8 hours (or dehydrator at 57°C) 5. Done when tacky but not sticky 6. Roll up in parchment, cut into strips

The Science: - Water evaporates, concentrating sugars, acids, and flavors - Pectin in fruit creates flexible texture when dried - Low water activity prevents microbial growth - Maillard reaction can occur during extended heating (browning)

Temperature and State Changes

Instant Ice Cream: Freezing Point Depression

Difficulty: Easy | Time: 15 minutes

Make ice cream in a bag using salt to lower freezing point.

Materials: - 120ml heavy cream - 120ml milk - 2 tablespoons sugar - 1/2 teaspoon vanilla - Small zip-lock bag - Large zip-lock bag - 2 cups ice - 1/2 cup rock salt (or table salt) - Towel or gloves

Procedure: 1. Combine cream, milk, sugar, vanilla in small bag, seal tightly 2. Put ice and salt in large bag 3. Place small bag inside large bag 4. Seal large bag 5. Shake and massage for 10-15 minutes (use towel - gets very cold!) 6. Remove inner bag, rinse briefly, open, and eat

The Science: \[\ce{NaCl(s) -> Na+(aq) + Cl^-(aq)}\]

Ice alone melts at 0°C
Salt dissolves in liquid water on ice surface
Ions disrupt ice crystal formation (freezing point depression)
Salt-water mixture can reach -18°C or colder
Cold enough to freeze cream mixture quickly
Fast freezing = small ice crystals = smooth texture

Experiment: Try different salt amounts. More salt = colder = faster freezing but potentially salty if bag leaks!

Summary: Chemistry Concepts Through Food

Experiment	Key Concepts
Meringue	Protein denaturation, foam stabilization
Cheese	Acid precipitation, isoelectric point
Casein plastic	Protein polymerization, bioplastics
Ceviche	Acid denaturation vs. heat denaturation
Honeycomb	Thermal decomposition, aeration
Caramelization	Pyrolysis, polymer formation
Maillard	Amino acid-sugar reactions
Rock candy	Supersaturation, crystal nucleation
Starch gelatinization	Polymer swelling, gel network
Mayonnaise	Emulsification, surfactants
Butter	Emulsion breaking
Gelatin gummies	Protein gelation, proteases
Agar jellies	Polysaccharide gelation
Jam	Pectin chemistry, water activity
Antioxidants / apple browning	Enzymatic oxidation, redox
Turmeric indicator	pH indicators, natural pigments
Oobleck	Non-Newtonian fluids, shear-thickening
Bread	Fermentation, gluten network
Popcorn	Phase transition, pressure
Color-changing drinks	Acid-base indicators
Pickles	Osmosis, preservation
Strawberry DNA	Cell structure, precipitation
Spherification	Polymer cross-linking
Ice cream	Freezing point depression

Resources

Books: - “On Food and Cooking” by Harold McGee (the definitive reference) - “The Food Lab” by J. Kenji López-Alt - “Modernist Cuisine at Home” by Nathan Myhrvold - “Cooking for Geeks” by Jeff Potter - “The Science of Good Cooking” (America’s Test Kitchen)

Websites: - Serious Eats: Food Lab - ChefSteps - Khymos (molecular gastronomy)

Videos: