Just wanted to add a few important points
When you see the fungal mat, you should either stir or end the process and clean the seed.It is fine to for it to stay there for a few hours or more, but not days.There is some evidence that the fungal mat could injure and or discolor the seeds.
Reference: Raymond, A.T.G., 1999. Vegetable Seed Production. 2nd Edn., CABI Publishing, Wallingford, Oxon, UK.
When I get quick fungal mats like I have been getting in 24 to 36 hours I see no reason to stir until I see a fungal mat.After that I stir a couple of times and let it sit another day, still within that important 3 day window.
Fermentation usually begins 12 hours after you start give or take and I think it is fine to stir before you see the fungal mat.But I also think it is important for a person who is doing a fermentation for the first time to see the fungal mat and stirring can delay that or can cause you not to get a fungal mat at all.
Also, I have read many research documents and their conclusions that the longer you ferment the more seed you will lose.I cannot as a rational individual dismiss this overwhelming evidence.There is even evidence that plant vigor of the seedling is affected with long fermentation.
Next up we will discuss the Lemon Juice method of tomato seed extraction which is close to being just as effective as fermentation
