Are we talking black scary stuff or a white film on the lemons? I think a white film is normal and just needs rinsing off anything more dramatic than that obviously needs to be tested on prisoners or students first.
I've just been googling around a bit and the Jamie Oliver recipe says wax free lemons. Your best bet for them might be an organic store or farmer's market or jump the fence of a garden with a nice fruitful tree (you could ask but that's not as exciting as midnight fruit theft).
His recipe also calls for squeezing lemon over the lemons.
I have preserved my own lemons as well.It was my first time and they turned out great,i actually added chilli to it so they are spicy as well.Seeing as my DH is moroccan i cook alot of moroccan food and they get used quite a bit.
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