When we talk about yeast fermentation, we often say that yeast needs sugar to ferment. While this is true, it is also true that the type of sugar matters. The amount of sugar matters. Also there are fermentable sugars and non-fermentable sugars, of course. But we also have to consider that yeast utilizes different types of sugar differently.
How Much Sugar Do You Need for Fermentation?
First, how much sugar does matter. Too little sugar, and you’ll have your yeast lying dormant and potentially producing off-flavors. Too much sugar, and your yeast will rush through the fermentation process, potentially get overwhelmed and stressed out, and produce off-flavors. Striking the right balance is essential.
Typically, you’ll want a minimum of .2 grams of sugar for every gram of yeast.
What Are Fermentable Sugars?
Now, what kind of sugar also makes a huge difference in your fermentation.
Because remember, we are dealing with a single celled living organism that has to break down the sugar it consumes to get energy and then expel carbon dioxide and alcohol as waste products.
In the sugar family, there are simple sugars and complex sugars, called monosaccharides and disaccharides. Monosaccharides only have one glucose molecule and are super easy to consume and convert. Disaccharides are trickier, with two or more molecules and they take more time to break down.
Grains, like those used to make beer, on the other hand, are rich in maltose, which is a disaccharide, composed of two glucose monosaccharides, which can be difficult to breakdown for yeast.
To help the fermentation process, brewers for hundreds of years have been germinating the grains, or soaking them until they begin to sprout and then drying them out.
This process kicks the maltase enzyme into action, which breaks the glucose molecules up, so they are easier to digest and ferment for the yeast.
Sucrose is a disaccharide sugar found in fruits and vegetables, most commonly in sugar cane and sugar beets. The purification process helps break down the molecules, so yeast can more easily digest the sugars and ferment.
In experiments, sucrose has contributed immensely to the fermentation process, which is why you will see some brewers adding cane sugar or high fructose corn syrup to their brew to help feed the yeast.
As opposed to fermentable sugars, some brewers and winemakers like to work with non-fermentable sugars once fermentation is complete, particularly when attempting to create a sweeter beverage.
Xylitol, stevia, maltodextrin, splenda, and erythritol are all naturally occurring sweeteners that can be added to a wine, beer, or cider once fermentation is complete that will increase the sweetness of the beverage without continuing the fermentation process.
In the end, which sugars you use during fermentation will depend greatly on what beverage or product you hope to create, how sweet you want that product, and how much you have invested in the entire fermentation process.
And, of course, as with everything related to fermentation, a willingness to experiment and gain insight from experience is key. The more you play, the more you learn.
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