Here is a very special way of recycling leftovers: simple, quick and delicious.
I have basically only bought organic lemons since I found this option.
Whenever I need lemon juice for a salad or something else, I peel the lemon with a zest ripper and put the zest in a jar with rapeseed oil.
After about a week I sieve the contents into a second glass of the same size and fill up the loss of oil.
Next lemon and the procedure starts over. That means, put the zest in the oil, which is already flavored with lemon, let it steep for 1 week, sieve and adjust the oil level.
Little by little I get an oil that tastes very strongly of lemon and has no acidity. I like to use it for fish, seafood and also desserts.
If I always keep the oil on the same sand, I always have a sufficiently strongly flavored oil on hand, even when I use it for cooking.