Resumen de Articulos de Levaduras

Only available on StudyMode
  • Download(s) : 97
  • Published : December 11, 2012
Open Document
Text Preview
How does temperature affect the fermentation of yeast?
In science, we stretched a balloon over the top of a bottle filled with sugar, warm water, and dry yeast. It inflated a little after a few minutes. We did the same thing with another bottle filled with sugar, cold water and dry yeast. The balloon didn't inflate. Apparently fermentation occurs more in hot temperatures than in cold. Why is this? Chemical reactions within yeast are facilitated by enzymes, which are large organic catalysts. Each enzyme has an "optimal temperature range" -- a temperature range at which it performs best. For many enzymes, the optimal temperature range is what we would perceive as warm -- about the same as normal internal human body temperature.

So: in the warm water, enzymes are within their optimal temperature range, and they catalyze chemical reactions more quickly, therefore the fermentation (which is a series of chemical reactions) proceeds more quickly.
Effect of Temperature on Fermentation
Temperature changes have profound effects upon living things. Enzyme-catalyzed reactions are especially sensitive to small changes in temperature. Because of this, the metabolism of a poikilotherm, an organism whose internal body temperature is determined by its environment, is often determined by the surrounding temperature. Bakers who use yeast in their bread making are very aware of this. Yeast is used to leaven bread (make it rise). Yeast leavens bread by fermenting sugar, producing carbon dioxide, CO2, as a waste product. Some of the carbon dioxide is trapped by the dough and forms small “air” pockets that make the bread light. If the yeast is not warmed properly, it will not be of much use as a leavening agent; the yeast cells will burn sugar much too slowly. In this experiment, you will watch yeast cells respire (burn sugar) at different temperatures and measure their rates of respiration. Each team will be assigned one temperature by your teacher and will share their results with other class members. You will observe the yeast under anaerobic conditions and monitor the change in air pressure due to carbon dioxide released by the yeast. When yeast burn sugar under anaerobic conditions, ethanol (ethyl alcohol) and carbon dioxide are released as shown by the following equation: C6H12O6 2 CH←→⎯3CH2OH + 2 CO2 + energy

glucose ethanol carbon dioxide
Thus, the metabolic activity of yeast may be measured by monitoring the pressure of gas in the test tube. If the yeast were to respire aerobically, there would be no change in the pressure of gas in the test tube, because oxygen gas would be consumed at the same rate as carbon dioxide is produced

Fermentation Temperature Control
Fermentation temperature control is the single most important thing you can do that will make the most dramatic improvements in your beer. And it can be a big problem, especially when brewing in the Deep South. Winter brewing is great but summer brewing can be brutal in the 100°+ days. Without temperature control, it's simply impossible to brew most beers correctly. Many homebrewers underestimate its importance and therefore are doomed to brew mediocre beers. Some of the major problems associated with fermenting too warm are: * The biggest problem is theoff flavors from esters and fusel alcohols that the yeast produce. Sometimes the flavors are not so much "off" as they are inappropriate for the style. * Your yeast can blast out of the starting gate, consuming everything in sight, then run out of nutrients before finishing the sugar. This usually ends in an incomplete fermentation. * Poor temperature control often results in fermentations that are too hot, causing the yeast to become too sensitive to alcohol toxicity (meaning that they will die off from the alcohol before their usual tolerance is met). * Yeast begin to die off from heat stress, leaving the remaining yeast to do all the work. In effect...
tracking img