Enzymes for a bit of blood from a paper cut in the case of my sheets. Soil is not suspended in soaking. Specific soils are meant to be dissolved or attacked before the main wash. I did not have to let my laundry soak overnight; it was just convenient.
Overnight soaking was a very important step in washing, especially in the days of washboards and wringer washers. The 3 to 6 minute Bendix Power Soak in warm water with the washing product was billed as better than overnight soaking, although according to Consumer Reports, in the original Automatic Home Laundry it was not shown to improve cleaning. The cool to warm water soaking, with washing soda or other caustic builder to make sure the water soaked the textile fibers, was to soften soil and assure the removal of any protein stains, like from undergarments, sheets from the master bedroom, or the teenage daughter or son's sheets or the crib sheets. As you know, protein is soluble twice unless it is cooked. That is why powdered blood is mixed with many plant sprays. The mixing is the second time it is dissolved and when it dries on plant leaves, it keeps the agent in contact with the leaves longer because it does not dissolve in the rain, although over time it does break down. This treatment of protein-based soils was important because, with a non-automatic, the linens were washed first when the water was hotest, often almost boiling, and without the cool water soaking, the stains would be set. In the time of the washboard, soaking was followed by rubbing on the washboard with a bar of lye soap and then, for linens, boiling to whiten and dissolve any small bits of soap so that they would rinse out and not turn the fabric yellow when it was heated by the iron. Loosening the soil by soaking resulted in lessening the need for back-breaking scrubbing on the board.
