As I mentioned a couple of weeks ago, I watched quite a bit of TV at the end of last semester.  One of the shows I watched was a show about celebrities who had lost amazing amounts of weight.  Most of the “amazing” part really came down to having enough money to pay for personal chefs, personal trainers, and nutritionists, or enough fame to have a company like Jenny Craig or Nutrifast pay for these things for them, but everyone once in a while they would credit the weight loss to something less likely than a good diet and lots of exercise.

For example: yeast.

Yeast is a misunderstood organism.  First off, it’s not an animal or a plant like you were taught as a child (I spent many misinformed years imagining tiny elephants living their lives inside those Fleichman’s packets), it’s a fungus like a mold or a mushroom.

Now yeast is used to make lots of foods because it’s good at two things: eating sugar and excreting carbon dioxide or alcohol or both.  You see this in bread where the carbon from the yeast creates the air pockets that make the bread light and fluffy, you see it in wine where the yeast creates alcohol, and you see it in beer where the yeast does both to make the alcohol and the carbonation.

What this E! show seemed to be saying was that consuming beer and wine would make you bloated because of the yeast in these drinks.  Umm…no.  While yeast does produce carbon dioxide during the creation of beer and bread eating or drinking these products will not fill your body with carbon burping microorganisms that will make you bloated.  The reason for this is that the yeast in these products is either non-existent or dead.

Let’s look a little more closely at how bread and beer are made.

Consider bread.  Bread is made using a species of yeast called Saccharomyces cerevisiae (notice the similarity to the Spanish word “cervesa” for beer), which is frequently known as baker’s or brewer’s yeast.  To make bread you first mix up warm water with some flour and sugar, then you add the yeast.  The yeast eats up the sugar and creates both alcohol and carbon dioxide. 

Bread isn’t alcoholic the way that beer is for two reasons: 1) the fermentation period is much shorter.  Bread rises for maybe 24 hours whereas beer ferments for weeks.  2) heat cooks off alcohol, which means that the tiny amount of alcohol that is created by the yeast is cooked off when the bread is baked.  This, by the way, is also why yeast from bread could never survive to final product that you eat: it’s all killed during baking.  There is no way for live yeast to survive the baking process and take up residence in your body.

Now let’s think about beer.  Beer is made using two types of yeast, the same Saccharomyces cerevisiae used to bake bread and Saccharomyces pastorianus.  These yeasts are also known as “top fermenting” and “bottom fermenting;” the former makes ales and the latter makes lagers.  However, at the risk of sounding incredibly repetitive, both of these yeasts work the same way: they eat sugar and excrete alcohol and carbon dioxide.

Unlike in bread where the carbon dioxide is the goal, the primary goal of using yeast to make beer is the alcohol (In most beers the bubbles come from an injection of CO2 rather than a yeasty secondary fermentation in the bottle.  This is because beers given a secondary fermentation have a cloudy look and a layer of dead yeast at the bottom of the bottle, which is unappealing to most consumers).  This is also why there is no chance that live yeast could move from a finished beer to your body. 

See, the yeast happily converts sugar to alcohol for as long as there is sugar to convert.  The problem for the yeast is that alcohol is deadly to it.  This means that eventually the alcohol content of the beer rises to a point where it is poisonous for the yeast and the yeast dies.  The same thing happens during wine production, although wine makers use a different type of yeast that can survive in more alcoholic environments.  In both cases the yeast is normally filtered out before bottling, so you don’t find it in the finished product.

All this is not to say that eating large quantities of bread or drinking beer and wine can’t make you gain weight and feel bloated.  It’s just that the yeast in these products is not responsible.  In both cases it’s excess calories, but in beer and wine it’s also an interesting metabolic process involving the alcohol.  More on that later, but for now it’s good enough to know that yeast, while interesting and useful, will not turn you into a beach ball.