Writing on a piece of white paper with lemon juice is a simple mechanism for hiding writing. If the paper is exposed to a heat source such as a warm lightbulb, the lemon juice will change color, exposing the message.
The juice of lemons used for flavouring, souring and to prevent cut fruit and vegetables from browning or to whiten fish and fish bones for stock. Cooking Tips: Before extracting the juice from a lemon, roll it on a hard surface and apply pressure with the palm of your hand. Boil the lemons in particular for 5 minutes to produce more juice. We could also bake them in the oven for 5 minutes at 160°C. If the lemons we have are not enough, replace a small quantity of lemon juice with 1/2 tablespoon vinegar for each tablespoon of lemon juice. To avoid the seeds falling in the juice, wrap a cloth around them when squeezing. If you need just drops of lemon juice then pierce a lemon with a fork and squeeze.