how to make brewers yeast!?

This is called culturing. It is a time consuming and laborsome process. It involves some knowledge of microbiology and sterile techniques yet anyone can do it. Remember the lay out costs will be high and you will not likely, for a long time anyway, recoup your capitol investment. [capital outlay] But it is a nice hobby and it will help you produce some superior beers. Here are some sites to help with the basic information on culturing yeast.

http://www.realbeer.com/spencer/yeast-culturing.ht...

http://www.unm.edu/~draper/beer/slantuse.html

http://www.maltosefalcons.com/tech/MB_Raines_Guide...

http://en.wikipedia.org/wiki/Aseptic_technique

Just a basis of knowledge you of course do not need to purchase a fume hood.

http://www.globalrph.com/aseptic.htm

http://www.engr.umd.edu/~nsw/ench485/lab8b.htm

If you can not find culturing equipment from a local brewing supplier or science shop then search online. Many will sell to you with just a credit card, I know because I make smei-regular purchases myself.

http://www.cbsscientific.com/index.asp?PageAction=...

http://www.microbeworld.org/microbes/tools_culture...

http://en.wikipedia.org/wiki/Brewing

Beers of Spontaneous Fermentation (wild yeasts)

Main article: Lambic

These beers are nowadays primarily only brewed around Brussels, Belgium. They are fermented by means of wild yeast strains that live in a part of the Zenne river which flows through Brussels. These beers are also called Lambic beers. However with the advent of yeast banks and the National Collection of Yeast Cultures,[2] brewing these beers, although not through spontaneous fermentation, is possible anywhere.

[edit] Beers of mixed origin

These beers are blends of spontaneous fermentation beers and ales or lagers or they are ales/lagers which are also fermented by wild yeasts.

[edit] The brewing process

The brewing process is typically divided into 7 steps: mashing, lautering, boiling, fermenting, conditioning, filtering, and filling.

Lambics are still brewed today and they represent the old way beer was fermented many years prior to the science disipline of microbiology.

http://en.wikipedia.org/wiki/Lambic

Brewers Yeast Wiki

Back in the day, beer was fermented in wooden barrels. If the brewers liked the end result, they simply fermented additional batches in the same barrel, recultivating the same yeast.

Today, homebrewers go to homebrew shops and buy the yeast. There's a lot to choose from.