Fermentation question

How do I know when to stop fermentation? And how do I do that without funny chemicals

The only way to stop fermentation is to pasteurize your brew. You can find out how to do that in the cider page. You can also add potassium sorbate after fermentation is complete to inhibit yeast reproduction and then back sweeten to your desired taste.

Fermentation will stop when it stops, there isn't a whole lot you (as a home brewer) can do to stop it.

One way is to let the yeast keep going until they drown in their own waste. That waste is the alcohol and most yeasts can't take more than 15 or so percent alcohol. This would be the least desirable method.

Other ways include sterile filtering (kinda expensive), pasteurization ( heat and wine,not good) cold crashing (not really easy for a home brewer) and finally chemically stopping the yeast from reproducing so that the leftover yeast cells eventually die of old age.

Those "funny chemicals" are the only easy way for a home brewer to stop a fermentation. The sulfites are naturally occurring and sorbate is found in almost everything you eat or drink. Its not that bad...