Another approach to laundry prewashes is oxidation.
This is an approach where fragile, intensely coloured dye molecules such as those in beetroot, red wine and grass are oxidised by an oxidising chemical. In years gone by, this was achieved by bleach. My mother used to get grass stains out of my cricket whites years ago by soaking them in bleach. It worked, but eventually destroyed the fabric.
A more modern approach these days is to use a gentler bleach that will still destroy the colours but not the fabric. This is generally achieved with perborates, compound salts that release hydrogen peroxide, a chemical that is just strong enough to do the job at low concentrations.
There are two laundry prewashes that use this approach – Preen Oxy Action and SARD Oxy Plus. The Preen works the better of the two. In a recent trial I did for Today Tonight of twelve different laundry prewashes, it was the only one that completely removed the red wine stain.