Shabbat 140 - Making mustard
In general, sorting on Shabbat is prohibited. However, what kind of sorting is that? - One that separates the bad from the good, because this is similar to the work done while constructing the Tabernacle. However, one may put an egg into a mustard strainer - that same strainer that was prohibited in the case of wine . Why? The mustard seeds in this case were already ground and strained before Shabbat and are found at the bottom of the strainer. The custom was to crack an egg in the strainer, so that the yolk would go down and color the mustard. The yolk just goes down and the albumen remains above. Since the albumen is not refuse but can be used, this is not sorting. And coloring the mustard is not prohibited since the prohibition of coloring does not apply to foods.
On the subject of food preparation, there was a bitter herb called asafetida, which people used to soak in water and drink for health reasons. This is prohibited on Shabbat because healing in general is prohibited - lest one comes to grind the medicine. However, if he soaks it in vinegar, then this is perfectly allowed: since it was a common condiment used at the table, one can eat it, even though it has a therapeutic effect.
Art: Joseph-Alphonse Planson - Still Life Of A Chocolatier, Together With Boiled Eggs, A Coffee Grinder, A Pipe And A Pouch Of Tobacco