What is Malolactic Fermentation (MLF)?
In prior posts, and in our own due diligence, we have learned about the basics of fermentation. May the entire subject be too complex or something you experiment with, you generally have a simple understanding of how fermentation works. But, did you know, in the chasm that is fermentation, and the general cider making processes, there are multiple ways to ferment? One of the lesser known fermentation process is known as malolactic fermentation, or MLF. It is a fermentation process that can actually change the entire flavor profile of your cider, making your plain cider a bit more funky. And that’s groovy.
Recently hearing about it ourselves, we had to explore this process and get an in-cider look from two cider industry experts. We spoke with Bryan Holmes, the co-founder of Citizen Cider (also heads up the cider making), and Bri Ewing, a clinical assistant professor at WSU Mount Vernon, who specializes in fermentation. Bri was paramount in helping us understand the process and be able to ask Bryan, a cider maker, quality question about MLF and his product, Wit’s Up. Between the two of them, we were able to get the answers we were looking for. Let’s explore.
So what exactly is MLF? This fermentation is a biochemical process performed by lactic acid bacteria, like Oenococcus oeni, which convert malic acid to lactic acid. We typically identify malic acids as sour flavors and lactic acid as much smoother or buttery in flavor. This process is popular not only in cider but also in wine and it is done by either forced MLF or natural MLF through the spontaneous growth of natural bacteria. Forcing the process involves pitching commercial bacteria, a more reliable method. Naturally-occurring MLF is variable and can have wild outcomes, creating off-flavors or smells.
The next question is when would a cider maker want to use MLF and, if necessary, how can it be avoided? In the simplest of terms, it is used when acid levels are too high to provide a balance of flavors, or, as Bryan says “aroma, sourness, astringency, and sweetness.” Sourness can also block fruit aromas and flavors from occurring in a cider. A cider maker would desire the process when a cider batch yields a product that is highly acidic and sweet, especially if a dry finish to the said product is desired. Controlling the malic acid and softening it up can vary widely depending on the type of bacteria strain and the degree in which it is used. This includes “compounds such as fruity esters, the buttery compound, diacetyl, and those that smooth the mouthfeel, such as glycerol. Inoculating with a commercial strain of malolactic bacteria during the primary or during aging can provide a variety of effects, good and bad, on the cider. Timing, good nutrition, and strain selection is critical” as Bryan said.
How can you functional stop MLF? There are a few good methods: sulfites, lysozyme, filtering, temperature, or agricultural practices. Sulfites are not always desirable but are highly effective in avoiding MLF, as well as lysozyme, skilled at reducing malolactic bacteria vastly. Low temperatures and filtering are effective against a lot of yeast strains and this is no exception. Finally agricultural practices like using fresh fruit that is in great shape can help limit the growth.
Naturally, we wanted to discuss a cider that uses MLF to distinguish it’s flavors & aromas. Wit’s Up, by Citizen’s Cider, does just that. They co-innoculate the malolactic in their primary fermentation. At this point, Bryan says there is much less stress on the bacteria because the ethanol levels are low and there is still an abundance of nutrients like nitrogen. For the product that uses the process, Wit’s Up has a very clean taste that is crisp and refreshing. There are notes in the cider that are very close to beer and the acids are softer. It feels carefully crafted and is a great transitional product for beer & wine fans alike. Honestly, we are huge fans of this cider before we looked at the complexity of the process. And who knew this fermentation talk would be so much fun?
In the coming future, we will be looking further into Wit’s Up in an upcoming review as well as an a thorough interview with Bri to understand her background and why she chose fermentation as an area of study.