Do i need beer yeast for cultivating my own beer yeast? because i tried to brew beer with bread yeast and the result was not satisfying. Also, in my country as an islamic country it's not easy to find beer yeast. thanks for your answer.
90% of the flavour of beer is from the yeast. It's important. But ... are you sure the undesirable flavours you encountered were from the yeast you used?
You really should use brewing yeast. Obviously you can buy yeast, or possibly grow up a small amount from a bottle of beer that has not been pasteurised.
For a long time bread yeast and brewing yeast were the same thing。It was not until 1883 when Emil Hansen isolated a single strain of yeast that the concept of "pure yeast brewing" came into beer production.
So if you cannot get beer yeast at all, using a bread making yeast would be the next best alternative. Most wild-captured yeasts perform much like a saison-type yeast, and have relatively low alcohol tolerance. Also it's difficult to remove other things from your microbial culture, like bacteria - which may add a sour note to your beer flavour.
Yeast produces the bulk of the flavour during the initial growth phase. So you can increase the flavour by using less yeast, or decrease the flavour by pitching more.
Thus I recommend you get a good quality bread yeast. Make a few batches with differing amounts, maybe starting around 0.2 grams per litre (i.e. 10g for 20 litres).
There is a great book called "Yeast" by Chris White & Jamil Zainasheff. It can tell you all you need to know about growing yeast.
In addition to this, it's very important to ensure all aspects of your brewing process are sanitary and your fermentation process is best-practice. It may be worth reading of a few brewing sites.
Well, first of all check your local legislation to make sure you're not in trouble with the law for making alcohol at home :)
Second, yes, to make e.g. beer of the taste you might be familiar with (e.g. english ale or european lager) you need a cultured yeast. While liquid yeast should be most likely too difficult to find, you could order dry yeast via internet (again, subject to legal restrictions). Google for something like "fermentis dry yeast" or "mangrove jacks dry yeast".
If you definitely can't get your hands on real yeast.. well, if I had such an issue, I'd try to cultivate something. After all, yeast are ubiquitous and exist everywhere, you just need to capture and tame the right kind. One option might be from wild yeast from grapes/fruits. To avoid conditioning of yeast on fructose (brewing yeast should be able to eat maltose), I'd just wash freshly picked grapes/apples with boiled lukewarm water and then add that wash into sanitary malt extract. In a rural environment, you might try and put out plates with malt extract solution overnight, collect them next morning, then incubate and check what taste you get within a couple of weeks. 1 from 5 chance you get something suitable, so you need to keep trying. Google "spontanous fermentation" for more details. Good luck!
You can make decent beer using bread yeast, and certainly stuff that you'll enjoy drinking. You might have a problem trying to match a particular style of beer with bread yeast, but you can easily make beer, wine and mead with bread yeast because bread, ale, and lager yeast are all Saccharomyces cerevisiae. They all eat the same kind of sugars, including maltose. Their differences are are more subtle in how they react to their environment (e.g., temperature, pH), what byproducts they produce, and how well they flocculate. You'll have a hard time making a classic German hefeweizen with bread yeast because you won't be able to produce its distinctive banana and clove taste, but you can make a tasty wheat beer, or you'd have trouble making a crisp and clear lager because bread yeast (in my experience) doesn't flocculate as well.
As part of a science fair project with my son, we went the other way and made bread using different kinds of yeasts. We used bread, ale, lager, two different wine yeasts, and a strain of Brettanomyces bruxellensis. We made a basic white loaf out of all of them and gave out samples for taste tests. They all made decent bread, but (I think) the lager and the brett did just as well as the bread yeast. Personally, my least preferred was the wine/champagne yeast EC-1118; there wasn't much yeasty flavor and it was pretty bland (though others picked it as their preferred).