“You won't consider a lab coat?” Brie Larson’s Elizabeth Zott in Apple TV’s Lessons in Chemistry asks her TV producer. “It has more surface area than an apron. I don't understand why everyone doesn't cook in a lab coat.”
Chemists Dr. Rebecca Yardley and Celia Du reacted to the Emmy-nominated series and paused at Elizabeth’s claim. Though neither of them had considered this, they decided it would only be scientific to test it out for themselves before taking a stance.
What better way to test out lab coats in the kitchen than making a refreshing, colour-changing (and potentially staining!) cocktail or mocktail? Repeat the experiment yourself by following the recipe below:
Ingredients
Colour-changing ice
24-30 dried butterfly pea flowers
2 cups of water
Lemon syrup
1 cup sugar
1 cup water
1 cup lemon juice (about 4-6 lemons)
Cocktail/Mocktail
Plain crushed ice
Soda water
(Optional) 2.5 oz alcoholic or non-alcoholic spirit, e.g. vodka
Materials
Mesh strainer
Ice cube tray
Sealable bag
Mug
Small saucepan
Glass
Instructions
Colour-changing ice
Combine butterfly pea flowers with boiling water.
Stir to combine and let steep for 4 minutes.
Strain the tea through a mesh strainer.
Pour the tea into an ice cube tray.
Place the ice cube tray into the freezer and freeze until solid, at least 4 hours or overnight.
Once frozen, crush the ice by placing the ice in a sealable bag and hammering with a spoon.
Lemon syrup
Place the sugar and water in a small saucepan and bring to a simmer.
Stir so that the sugar dissolves completely and remove from heat.
Juice the lemons and add the juice to the simple syrup sugar water.
Cocktail/Mocktail
Crush plain ice cubes using the same method as above.
Fill glass halfway with plain ice.
Then fill the glass the rest of the way with the colour-changing ice.
Pour in 2 oz lemon syrup.
Add 2.5 oz alcoholic/non-alcoholic spirit (optional).
Finish off with as much soda water as you like.
How does it work?
The butterfly pea flower contains a family of molecules called anthocyanins, which act as a pH indicator. pH, an abbreviation of “power of Hydrogen,” relates to the concentration of hydrogen ions (H+) floating around. When we say a solution is acidic, what we are actually saying is “there are a lot of H+ ions in here!” The more acidic it is, the lower its pH is on the scale of 1-14. A solution is neutral when its pH is 7 and basic (or alkaline) when the pH is higher. A pH indicator are ‘halochromic’ molecules, which means they reversibly change colour depending on the range the solution falls within on the pH scale.
Anthocyanin molecules are blue when the solution is neutral or slightly basic. As acid is added, the solution changes colour, turning first purple then pink. This range from purple to pink is caused by different ratios of molecules turning pink to those that remain blue.
These molecules are also responsible for many of the red, blue and purple colours you see in nature! Red cabbage, blueberries, açai, blackberries and purple corn all have this family of compounds to thank for their amazing colours! This is also the reason you can make pH indicators from red cabbage because it contains similar compounds!