Lye + water + oil = soap

Fiona would like to be a chemist, or so she thinks. Until we get to the chemistry section in her science course, we’re having fun little forays into the world of household chemistry.

We had fun making soap a couple of weeks ago. We used a combination of sweet almond oil, olive oil and coconut oil, and a great on-line lye calculator. We weighed things out with our digital kitchen scale (love that thing!) and got a mixture that was accurate and reliable. Much better than the guess-work I’d been used to from my previous soap-making forays.

We added some rosemary and lavender, and essential oils of each, plus a little green soap dye. It smells lovely and we are patiently waiting for it to cure whilst testing out little scraps from time to time. It lathers beautifully.

Sugar syrup + baking soda = foam

Today we made sponge toffee. I hadn’t done this in years and had mistakenly thought it was a acid-base reaction with the baking soda which was responsible for all the bubbles. In fact the baking soda remains inert and simply acts as an nidus for bubble formation in the boiling syrup. There’s no acid involved at all: just the thermal decomposition of sodium bicarbonate.

We made our sponge toffee with a bit of butter rum flavouring left over from Sophie’s summer hard candy business and it tastes fabulous. Our digital infrared thermometer made easy work of the syrup boiling. Again, good tools make such a difference!

Sponge Toffee


2 1/2 cups sugar
2/3 cup corn syrup
90 ml water
2 tsp. vanilla extract
1/2 tsp. butter rum flavour (optional)
2 tsp. sifted baking soda

Line a 9×13″ pan with foil and brush foil with oil or butter. Mix sugar, corn syrup and water in a large heavy saucepan. Bring gradually to a boil. Cover with tight lid for 5 minutes to dissolve any sugar crystals that may be adhering to the sides of the saucepan. Remove lid and continue boiling, checking temperature frequently. Once syrup has reached 300ºF, remove from heat. Stir in flavouring(s). Whisk in baking soda and quickly pour into prepared pan. Allow to cool to room temperature. Remove foil and break apart, consuming ad lib.

Chemistry around here