Alan Bradley said this quote

I had found by experience that putting things down on paper helped to clear the mind in precisely the same way, as Mrs. Mullet had taught me, that an eggshell clarifies the consommé or the coffee, which, of course, is a simple matter of chemistry. The albumin contained in the eggshell has the property of collecting and binding the rubbish that floats in the dark liquid, which can then be removed and discarded in a single reeking clot: a perfect description of the writing process.