Have you even heard someone comment about fusel alcohols or higher alcohols and wonder what they were talking about? It’s not the fuel used to power rockets to the moon. That was actually liquid oxygen, liquid hydrogen, and kerosene. When yeast convert sugar into alcohol, ethanol is what most of that alcohol is. However, it can also create stronger alcohols call fusel alcohols or higher alcohols. These alcohols are one of many compounds that are created during the fermentation process. These alcohols are not the poisonous methanol that can be produced through distillation, which is why most countries highly regulate or forbid home distillation.
In general, you will hear most people talk about them in a negative connotation. However, that is not necessarily true. Like most things involving fermentation, there is a balance that you are seeking to achieve. Fusel alcohols add aroma and flavor just like esters, phenols, and other compounds. These are what define beer and wine styles as well as some hard ciders. The farmhouse aromas of leather, barnyard, spice, clove, and similar earthy elements are what make these hard ciders the farmhouse style. Without these compounds, you wouldn’t have farmhouse. If they make aromas and flavors, you might be thinking the more the merrier. But, that also isn’t good. When you get too many of these compounds, they overwhelm and are often considered faults.
Fusel alcohols along with other compounds can also have negative health effects as they are said to be the source of headaches and or digestive irritation. They are by-products of the fermentation process and often associated with some type of deficiency in that process. Those deficiencies are numerous and can include the following.
- The fermentation happens at too cold or too hot of a temperature for the yeast used.
- The fermentation has temperature swings from hot to cold.
- The juice has too much or too little (more common) oxygen in it.
- The juice lacks nutrients like nitrogen, amino acids, or enzymes.
- The yeast count was too low (Example: under pitching).
These are just a few examples of what can create off flavors, which are flavors not true to the expected results of the yeast you use. Fusel alcohols are just one of these off flavors but, they are common enough that it’s good to understand what creates them, how to identify them, and what you can do about them. As you know if you’ve read my book, I do like to get into a little of the science. So let’s explore fusel alcohols and how they are created during the fermentation process.
Fusel alcohol are generally created in the lag phase of fermentation. In his book, Yeast, Chris White defines three phases of fermentation: Lag, Exponential Growth, and Stationary. The Exponential Growth phase is when the yeast reproduces and creates ethanol. However, this process is actually an anaerobic fermentation. That means it doesn’t use oxygen. Where the oxygen is needed is to support the lag phase. This is when the yeast processes various components and prepares all the elements they need to reproduce and create the ethanol and CO2 we desire as home hard cider makers. Oxygen is critical component in generating the proteins the yeast will need in the Exponential Growth phase. But so are other component like nitrogen and amino acids. If the juice is lacking the needed nutrients, the yeast will find ways to create them. That is where the fusel alcohols are created. That is also where a lot of the esters, phenols, and another aroma and flavor compounds are formed. The yeast will work to process compounds to create the nitrogen and others elements it needs to reproduce if they aren’t available. This extra work or stress on the yeast is what creates the esters, phenols, and fusel alcohols. This is the argument for using yeast nutrients. The goal is to ensure healthy reproduction of the yeast with minimal stress.
I respect this approach. My only concern is that most research has been done for beer and wine. Beer has malt sugars that can be complex and hard for some yeast to ferment. This is where beer yeasts have attenuation ratings as to how much of the malt sugars they can process. Wines generally have higher alcohol by volume (ABV). This is because the grapes have much higher sugar levels and the yeast used is most likely to ferment the sugars found in grapes fully. Grapes don’t have malt sugars like beer. Therefore, wine yeasts don’t really have an attenuation level. It is normally, 100%. Wine yeasts will generally make any hard cider dry because apples don’t have enough sugar to reach alcohol levels that would kill most wine yeasts. If you want a naturally sweet hard cider, what is the answer? There must be yeasts or processes we can follow that will not produce excessive off flavors and leave some residual sweetness. I refuse to believe the only viable solution is to ferment all ciders dry using wine yeast and back sweeten after treating the hard cider with sulfite and sorbate preservatives. That does bring up the questions, how do you know if you have too many fusel alcohols and what do you do with them if you do have too many.
Fusel or high alcohols, which tend to predominantly be amyl alcohols, have a distinct aroma. There are 8 varieties of amyl alcohols but they all contain 5 carbon molecules, 12 Hydrogen molecules, and one oxygen molecule in various configurations. This is different from ethanol’s chemical formula, C2H6O, which has fewer carbons and hydrogen molecules. Amyl alcohols are often used in solvents, which is why the aroma can be one of the key ways to identify them. The other is taste. They tend to have a distinct burning sensation. In small amounts, these aromas and warming sensations can be pleasant and even desirable. In larger amounts, it might seem like you are trying to drink rubbing alcohol or nail polisher remover. You can have a gas chromatograph performed, which will tell you the alcohol types as well as other compounds in your hard cider. However, the equipment needed isn’t cheap and most likely out of reach for most home hard cider makers. The taste and smell method will have to suffice.
If you have found yourself with a hard cider that smells like solvent and does more than warm your throat, there are some methods to help address these fusel alcohols. The first is the standard fix for many hard cider issues, which is time. Fusel alcohols are slower to be processed by yeasts so allowing your hard cider to age, should give the cider time to help reduce these naturally. They are also more volatile, which should allow them to dissipate if you age them. You can also remove them through carbon filtration. This is how some spirits are prepared and you could use a similar approach with your hard cider if you find your cider smells like solvent or burns your throat as they go down. While there are still scientific debates about whether fusel alcohols cause headaches or not, aging and carbon filtering are still your best two options for headache inducing hard ciders even if they don’t smell like solvent or taste like fire. Other compounds known to cause headaches may be present that time or carbon could also eliminate.
Ultimately, like most things in life, a little of something can add spice and interest to life and fusel alcohols are like that. They can bring some great aromas and sensations to your hard cider but can also quickly overwhelm a cider and may cause headaches. As I often state, your yeast and your fruit are the most important ingredients for determining how your hard cider will turn out. The best way to manage your yeast is to experiment and take good notes. We still have a lot to learn about yeast and how it ferments hard cider.
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