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Live yeast cultures are pure, which means they contain no contamination or other organisms. Live yeast cultures are also available in many more varieties than dry yeast, since not many yeasts can be dried successfully. 

If you replace dried yeast with a live yeast culture, you'll improve the quality of the beer.  Good yeast makes beer with better flavor and aroma.

Dried yeasts are changed by the drying process.  The drying process leaves physical scars on the yeast cells as evidence.  Because yeast reproduces by budding, every cell in later generations will show these changes, too.  All dried yeasts have a characteristic flavor, so all f the beers made with them tend to have the same flavor.  Live yeast cultures have much more variety.

It’s easy to pick a live yeast culture to match your beer style.  Your choice of which yeast to use will effect the beer in a number of different ways, most importantly in attenuation, flocculation, and flavor.

Attenuation is the amount of sugar consumed by the yeast during fermenting. 

If your wort has an original gravity of 1.040 (realize that 1.000 is water, and the remaining portion, .040, is dissolved sugars).   During fermentation the yeast will consume a certain percentage of the sugars in the wort.  This causes the specific gravity to drop.

Let's assume that an example yeast is supposed to have an apparent attenuation of 75%.   That means you should observe a 75% reduction in dissolved sugars during fermentation. 

Therefore, after fermentation, the specific gravity should have dropped to about 1.010 (the original sugar content of .040 has been reduced by 75%).

Using less attenuative yeasts produces beer with higher finishing gravity.  Higher finishing gravity is due to more residual sugars in the beer, this gives a beer more malt sweetness and fuller body.  Lower finishing gravities, from more highly attenuative yeasts, will produce a beer with lighter body and little or no malty sweetness.

Flocculation is the tendency of yeast to clump together, and therefore to fall to the bottom of the fermentor. Highly flocculant yeasts settle to the bottom of the fermentor quickly, which clarifies the beer. Yeasts with low flocculation tend to stay suspended longer, such as in hefeweizen. Gelatin will clear non-flocculant yeast.

Flavor, to a greater extent than attenuation and flocculation, will depend on your fermentation temperature. As a rule, a cooler fermentation will proceed slower but yield a cleaner flavor. As the temperature rises, fermentation is faster and produces more by-products. Some are described as fruity, spicy, minerally, tart, smooth, soft, etc.. If you want the flavors of malt and hops to dominate the beer, choose a clean yeast and ferment at the cooler end of the yeast’s temperature range. Many beer styles, however, rely on the yeast to contribute flavors to the beer, especially wheat beers. The warmer you ferment these styles, the more of the yeast’s distinctive flavor characteristics will be evident in the finished beer.

Temperature is especially important for lager yeast, since they ferment below normal room temperatures. The best way to produce lagers is to have a refrigerator with a temperature controller which will let you maintain any temperature effortlessly. Used refrigerators are very cheap, and can usually hold 2 fermentors. If you don’t have temperature control, put the fermentor in the coolest part of your house.

Some people ferment lagers at room temperature with good results. The secret to good room temperature lagers is the selection of proper yeast strain.   There are two main genetic families of lager yeast... the Carlsberg and the Tuborg strains. 

Carlsberg lager yeast strains are indigenous to Germany, and many other continental European regions.  They produce good lagers when fermented at low temperatures, in the 48-58 degree range.  Only after fermentation is the beer "lagered," which means that it is put into extremely cold (near freezing) storage to smooth and mature for a few weeks or months.

Tuborg lager yeast strains are much better at making lagers at higher temperatures, up into the mid 70's.  WYeast #2007 and #2278 are good examples of these yeasts.  At the higher temperatures, your beer may be somewhat harsh when you bottle it, but some time in the refrigerator will smooth it out considerably.