Butterscotch Beer Off Flavor: What Causes It?
There exists a great misconception about butterscotch beer off flavors and about off flavors in general as they tend to get a bad reputation as spoilers of beer.
In point of fact, most of the flavors and aromas we love in beer come from the same origin as those “off flavors.”
So, what makes a flavor an off flavor? Where do we get butterscotch beer off flavors? And what can we do about it?
The Role of Yeast in Fermentation
First, it is critical to understand that almost all flavors and aromas in beer outside of the grain and the hops come from yeast.
Strange, right?
You would not think that such a small microbe would have such a large impact, but it does.
Yes, you can create texture and flavor by using varying combinations of wheat and barley or working with oats. You can malt your grain more or less.
And hops certainly add an element of bitterness and herbiness to your beer.
But without yeast, you basically just have oatmeal, mead, or cream of wheat.
Yeast is almost magical in its performance during fermentation.
We tend to think of yeast only as contributing alcohol and carbon dioxide, but it does so much more than that.
And it undergoes an entire process during fermentation that allows for interesting blends of flavors and aromas.
After the brewers has ground the malted grain, boiled it and steeped it, and added hops, it really comes down to the yeast and what it can do.
The best thing a brewer can do at this point is facilitate the yeast’s job of fermentation to the best of our ability, and this is where the craftsmanship really comes into play.
You see, during fermentation, yeast cells convert cereal derived sugars into ethanol and CO2, but they also produce hundreds of secondary metabolites that influence aroma and taste.
And each substrain of Saccharomyces cerevisiae (ale yeast) and Saccharomyces pastorianus (lager yeast) has its own metabolites, which means brewers have hundreds of aroma and flavor profiles to experiment with.
Bacteria in Fermentation
Add to the work yeast does the added potential of bacterial influence, and you have even more flavor and aroma profiles to choose from.
Again, bacteria get a bad reputation in typical human conversation.
We only talk about bacterial infections and how we try to avoid bacteria with all of our anti-bacterial soaps and antibiotics.
Of course, in some cases, avoiding or getting rid of bacteria can be a good thing, even a lifesaving issue.
But there are also hundreds of beneficial bacterial colonies, like the ones alive and well (ideally) in the human gut.
Humans have been coexisting and thriving alongside yeast, bacteria, and even viruses for as long as we have been alive, and quite often it is the good yeast and the good bacteria that will kill off their bad counterparts for us.
It’s all about balance.
From the beginning of brewing, thousands of years ago, bacteria have been involved in fermentation, joining yeast to contribute to the flavors and aromas. And because bacteria contribute in the form of lactic acid (the same compound that creates yogurt, kefir, and kimchi), beer has always been a bit on the sour side.
Since Industrialization, however, we learned to control for bacteria, and have largely seen it as a bad thing in beer, until more recently when craft brewers have allowed the reentry of bacteria into our realm of awareness in brewing.
Off Flavors
By off flavors, we usually mean unwanted flavors in beer, and that can often mean just a little too much of something.
And those off flavors can come from either yeast or bacteria.
If we want beer to be sour, but not too sour, we would call it an off flavor if we are overwhelmed by sourness.
If we like a hint of banana or butterscotch, we only call it an off flavor if there is too much of those notes for our senses, so we cannot enjoy the beer.
Rarely, we find an off flavor that is simply not palatable at all, like the baby vomit flavor that comes from a butyric acid metabolite that has a very, very low flavor and aroma threshold. Once you can detect it in beer, it ruins the whole experience.
Most “off flavors,” in contrast, are not only acceptable but even desirable in specified quantities.
Diacetyl
The butterscotch, or buttered popcorn, off flavor is one such example.
It comes from a metabolite called diacetyl, which is naturally produced by yeast during fermentation, and can also be produced by bacteria, so if you have both in your beer, either intentionally or unintentionally, you will want to control for it, so it does not become overwhelming.
Diacetyl is much adored in many foods and is in fact the same amino-acid metabolite that is added to popcorn, to butterscotch candy, and is found in buttermilk to add that buttery flavor.
You just don’t want to overwhelm your beer with it.
How to Resolve Butterscotch Beer Off Flavor
Most often, if your beer has too strong a butterscotch beer off flavor, it is either because the beer has not been allowed to undergo its diacetyl rest or because you have unidentified bacteria exposure, perhaps in your lines.
This resting period explains why butterscotch beer off flavors have not been a constant source of concern for brewers.
Over time, they discovered that while yeast may make the mess, it will also clean up its own mess.
To resolve the too strong flavors, brewers will raise the temperature of their wort just a few degrees toward the end of fermentation, agitating the yeast, which signals the yeast to come in and “mop up” any residual metabolites that have not integrated well into the beer.
It really is an amazing science.
The other step you can take is to ensure your lines are sanitized and you don’t have a hidden bacteria waiting to increase your diacetyl levels in your beer.
Either way, this process is one you will hone over time, getting better and better at identifying too much of a good thing.
Cheers!
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