A common concern on homebrewing forums is, “Help! I’ve got a stuck fermentation”—an “unfinished” fermentation, where the final gravity of the beer is higher than the brewer expected it to be or higher than what would normally be expected of the yeast strain being used. Often, the issue is not a true stuck fermentation at all. Sometimes the brewer used a refractometer to check final gravity instead of a hydrometer and failed to account for the false reading due to the alcohol in solution. Sometimes the mash temperature for the beer in question was high, resulting in a higher concentration of unfermentable sugars and thereby rendering the brewer’s expectations of appropriate FG as unrealistic. Sometimes the beer’s FG is slightly higher than what the recipe or recipe calculator stated, even though the level of attenuation is in line with what can be expected from that yeast strain.

Simple solutions exist for the problems mentioned above: use a refractometer calculator to adjust the reading; perform a forced fermentation test to have an accurate expectation of FG; ensure your thermometer is calibrated to avoid mash temperatures that are too high; and calculate the percent attenuation the yeast has achieved and compare it to the range that is normally expected from that yeast strain (which can generally be found on the yeast manufacturer’s website). Sometimes though, the issue truly is a stuck fermentation due to poor yeast health, under-aeration, under-pitching, or any other number of yeast-related issues. If this is truly the problem, then raising the temperature of the fermentor and rousing the yeast, pitching more yeast (same strain), adding a small portion of actively fermenting wort (krausening), or pitching a more attenuative or alcohol-tolerant strain into the beer are practices that will generally yield good results if applied correctly.

The problem comes when some people take that last idea and run with it. If pitching a more alcohol-tolerant strain (for high gravity beers) or a more attenuative strain works, why not use champagne yeast? It’s a recommendation that I’ve heard many times (typically for high gravity beers), but it is usually a bad one. Even though champagne yeast can produce bone dry wines at high alcohol levels (showcasing its ability to be highly alcohol tolerant and highly attenuative), one cannot simply take those truths at face value and apply them to beer.

Champagne Yeast and Sugars

Champagne and other wine yeasts can bring a wine down to an FG of below 1.000. That said, the makeup of sugars in wine must is far different than what we find in beer. The sugars that make up the must are simple, single-molecule sugars, and wine yeast is excellent at fermenting these sugars. Wort, however, is made up of a much more complex matrix of sugars. In addition to simple sugars, there are also double and triple-chain sugars (in particular maltose and maltotriose) and more complex, unfermentable sugars. Ale and lager yeast strains are capable of and efficient at utilizing maltose and maltotriose (though some strains are able to ferment this to a lesser degree than others). Most wine yeast strains, however, are at best moderate consumers of maltose and incapable of fermenting maltotriose at all. Exceptions do exist, but these strains are the exception and not the rule, and none of them are champagne yeast. In fact, most wine strains of yeast are only capable of hitting somewhere around 50% attenuation in wort.

Ale and lager strains tend to consume simple sugars first before they move on to the harder work of fermenting maltose and maltotriose. So if a stuck fermentation is the problem, it is highly likely that those simple sugars are gone by that point and adding champagne yeast will do nothing.

Champagne Yeast is a Killer

Though it’s true that champagne yeast can be used effectively in the brewing process, it’s not generally done in the primary fermentation. Some commercial breweries utilize champagne yeast for bottle conditioning or in a stagger-pitched method—though not at the same time as an ale or lager strain (co-pitched). Homebrewers and some commercial breweries use champagne or other wine yeast to increase the alcohol of a beer after primary fermentation is done by doing a true secondary fermentation, e.g., adding simple sugars to the finished beer and pitching wine yeast. One brewery near me uses this method to produce their extremely high ABV anniversary beer by adding champagne yeast to the finished beer and then continually adding simple sugars in small doses.

There is at least one very good reason to never add champagne yeast to a beer that has not completed fermentation: champagne yeast is a killer. In fact, most wine strains are. Most wine yeasts have what is called a kill factor, which is a competitive strategy used by those yeast strains to ensure they are the ones who survive and get to consume the available sugars. There are a couple different categories of these yeast with the kill factor, with some yeast not being impacted by another yeast’s production of these toxins (to clarify with the use of the word “toxin,” these toxins do not impact humans—only other yeast). However, almost all ale and lager strains are sensitive to the kill factor and will be rendered useless to finish fermenting the beer. Since this compound remains in solution, pitching another yeast later (unless it’s not killer sensitive) will also do nothing. Adding champagne yeast to a beer that has not attenuated properly is an almost guaranteed way to ensure the problem will never be solved and that the beer will not attenuate any more.

I did manage to find a couple charts that show some known wine strains that have this kill factor and which are sensitive/not sensitive to it, but I was unable to locate any research on which ale and lager strains might be resistant to the kill factor. But again, almost all beer yeast are killer-sensitive.

Real World True Facts

Besides just spouting out some facts about yeast metabolism and some strains’ ability to produce a compund that is toxic to other yeast strains, I wanted to have some actual numbers to add to the conversation. I thought it might be somewhat difficult to purposefully create the environment for a stuck fermentation and be able to ensure that my yeast would peter out with enough fermentable sugar left to test anything with any reliability; so instead, I decided to test the attenuation of a champagne yeast, ale yeast, and (pseudo) lager yeast side by side in the same environment. I completed this attenuation comparison in a small amount of high gravity wort in order to both amplify the effects and also replicate the scenario for which I generally see people recommending the use of champagne yeast to help dry out or finish off a beer.

Armed with a couple mason jars and a pound of dry malt extract, I set to work.

I boiled the DME in one half gallon of water in order to produce a high gravity wort. After chilling the wort in an ice bath in my sink, I took a gravity reading. Adjusting for temperature, the OG of this wort was 1.094.

At this point, I split the wort into two mason jars and a one-gallon carboy. I put 16 ounces of wort into each mason jar and 32 ounces of wort into the carboy. (I had other plans for a further test with the wort in the carboy after this comparison, which was the reason for the difference in volume; unfortunately, I screwed up, so that further testing ended up being meaningless.) I then weighed out 2 grams of US-05 ale yeast and 2 grams of EC-1118 champagne yeast and pitched each (dry) into separate mason jars of wort. My calculation showed this to be an overpitch by a good bit, but I wanted to ensure that these worts showed full attenuation by each strain.

I also had a slurry of WLP-810 San Francisco Lager yeast from a previous brew, and as that yeast is only moderately attenuative, I opted to use that as a counterpoint in the other 32 ounces of wort. I sanitized a spoon, pulled a small amount of slurry out, and added this to the wort that was in the carboy. This method was far less calculated than pitching the dry yeast by weight, but even if I under pitched by a fair amount, I figured that would provide another (though less exact) comparison to the attenuation of the champagne yeast. If you’re inclined to do so, feel free to ignore this third wort since the volume, container size, and pitch rate added additional variables into the mix.

I left the wort to ferment and noticed some immediate differences. The wort with EC-1118 began vigorously fermenting within 2 hours and activity seemed to stop within the first day or two. The batch with US-05 progressed along with what I would consider a standard fermentation timeline (based on appearance alone). The carboy containing the wort with WLP-810 took longer to get started and was a much less vigorous fermentation. I also noticed that the finished beer fermented with US-05 was a little lighter than the beer fermented with champagne yeast. My first thought was to wonder if the difference in color was due to more sugars remaining in the beer fermented with EC-1118, but even if the final gravities ended up being different, I had no way of verifying that that was the sole cause of the color difference. The more I thought about it, the more I also realized that this color difference was likely due to having more yeast remaining in suspension (as US-05 is known for not being very flocculent).

Once signs of fermentation had stopped in all beers, I took some gravity readings:

US-05: 1.020 FG 9.7% ABV 77% attenuation

WLP-810: 1.025 9.1% ABV 72% attenuation

EC-1118: 1.034 FG 7.9% ABV 62% attenuation



Judging by these final gravity numbers alone, it seems that the champagne yeast could not handle as much of the sugars in the wort as either beer strain could. The additional gravity points (and subsequent ABV difference) shows the champagne yeast’s inability to ferment more complex sugars. Even the moderately attenuative lager yeast performed better in this wort than the champagne yeast. The 9 gravity point difference (WLP-810) and 14 gravity point difference (US-05) seem to indicate that both of these beer strains perform better than EC-1118 in a high gravity wort, likely due to the wort’s composition.

If we want to ignore the lager yeast fermentation since there are additional variables that I did not control for, the ale yeast performed better in a side by side fermentation. Extrapolating this, it makes sense that this ale yeast would also perform better in restarting a stalled fermentation where most (or all) of the simple sugars in the wort have been consumed.

I’m aware that my test was not perfect, nor is it a direct test of these yeasts in a stuck fermentation; however, if the beer yeast is more attenuative than the champagne yeast in an environment free of the extra stresses of limited oxygen and additional alcohol, then it makes sense that they would still be more attenuative than the champagne yeast in the more stressful environment. To put it another way, the added stress will only inhibit the yeast; it would not make any yeast perform better, including the champagne yeast.