Can Yeast Metabolize Artificial Sweeteners?
Many brewers, bakers, and others in the fermentation and yeast industries are interested in yeast metabolism and fermentation. And in the age of low fat, low sugar, low gluten, low everything, the question will inevitably come up, “can yeast metabolize artificial sweeteners?”
The answer is almost certainly no. Yeast needs fermentable sugars.
But sometimes, artificial sweeteners contain fermentable sugars, so it can be a bit tricky.
Let’s discuss.
Yeast and Fermentable Sugars
First, let’s cover what yeast can do.
Yeast is a single celled eukaryotic living organism existing, it seems, for one purpose, to find fermentable sugars as an energy source, consume them, and then produce as waste products alcohol and carbon dioxide.
That is, as far as science can tell us, what yeast cells have been doing for millions of years, if not hundreds of millions of years.
Yeast cells are microscopic, but they group and travel together, collecting on sugary surfaces like plants, on our skin, and in the atmosphere, constantly seeking their next sugar source.
Yeast can break down some carbon sources, like organic acids and amino acids, but those sources provide very little energy and as a result very little waste (alcohol and carbon dioxide). Yeast cells clearly prefer what we call fermentable sugars – hexoses like glucose, fructose, galactose, and mannose, or disaccharides like maltose and sucrose.
By far its favorite, the most fermentable of all sugars, is sucrose, which we find occurring naturally in sugarcane, sugar beets, dates, honey, and sugar maple sap.
Sucrose is 100% fermentable, which means yeast can convert sucrose in its entirety.
The ability of yeast to ferment sugars, and to what extent, depends largely on the molecular structure of those sugars. Indeed, through acts like roasting or boiling various foods, we can actually release enzymes in those foods that change their molecular structure and make them easier to ferment.
This reality is why we malt barley and other grains for brewing, to make them easier to digest, and by extension ferment, for yeast.
In general, most artificial sweeteners cannot be metabolized by yeast because of their very artificial nature.
What Are Artificial Sweeteners?
Artificial sweeteners are, by definition, not natural and are not sugar. Yeast will only ferment sugar.
Artificial sweeteners are created through a chemical synthesis process in a lab. Even those made from plant extracts are still created through synthetic chemical pathways that produce an end result distinct from the molecular structure of fermentable sugars.
In short, yeast does not recognize artificial sweeteners and so is not activated by them.
Sweeteners like Splenda, Stevia, aspartame, Sucralose, Saccharin, Xylitol, and Acesulfame K are all chemically produced and metabolically similar to each other but highly differentiated from naturally occurring sugars that are fermented by yeast.
Can Any Artificial Sweeteners Be Fermented?
The exception to this rule, that yeast cannot ferment artificial sweeteners, comes into play when artificial sweeteners are packaged with naturally occurring sugars, like dextrose.
Still, it will take yeast much longer to activate any small sugars and leftover enzymes in order to ferment and produce a viable beer or wine.
Further, yeast, if left with no alternative, may ultimately work hard to break down some artificial sweeteners like Splenda, but it will take so long that you may still end up with stressed out yeast that stagnate.
Use of Artificial Sweeteners in Brewing
Where artificial sweeteners are sometimes used in brewing is in the sweetening of the beer, cider, or even wine after fermentation is complete.
Some brewers and winemakers worry that adding too much fermentable sugar to make a sweet end product will naturally restart fermentation with any remaining yeast in the liquid and produce more alcohol and carbon dioxide.
This extra alcohol will surpass the expected ABV, and the extra carbon dioxide can lead to exploded cans, bottles, and casks.
Thus, brewers and winemakers may add Splenda, Stevia, or another artificial sweetener in order to make the beverage a bit sweeter without those worries.
Still, the pushback from a lot of brewers and winemakers is that artificial sweeteners, while not continuing the fermentation process, are responsible for an undesirable after taste.
As with most things brewing and winemaking, it is up to the individual brewer, and his or her loyal fans, to decide which flavors and aromas work best with which sweeteners.
This decision will necessarily arise from a wealth of experimentation.
Cheers!
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Sources:
- https://agsci.oregonstate.edu/sites/agsci.oregonstate.edu/files/bioenergy/k12/brewingbiofuels_interactive.pdf
- https://chem.libretexts.org/Bookshelves/Biological_Chemistry/Fermentation_in_Food_Chemistry/01%3A_Modules/1.10%3A_Yeast_Metabolism
- https://www.frontiersin.org/articles/10.3389/fmolb.2014.00017/full
- https://www.researchgate.net/figure/Yeast-energy-metabolism-Yeasts-have-two-pathways-for-ATP-production-from-glucose_fig3_273511895
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