Alcohol Fermentation


Let us start by saying that alcohol is quite easy to make. Humans have been making hooch for thousands of years, and for one very good reason: it alters our consciousness. In nature, not many substances have the power to alter minds, and the ones that do are highly revered and coveted. The pursuit of this mind-altering buzz has built entire empires, is likely responsible for the advent of settled agriculture, and has changed the course of human history.

While making alcohol is quite simple, making really good alcohol is something else altogether. The fermentation science is very complicated, and each type of alcohol—wine, beer, mead, cider—has its own very different requirements, processes, and fermentations. For this reason, in this section we will be discussing the alcohol fermentation in a broad sense, as there are commonalities with all the previously mentioned alcohol ferments. For example, wine fermentation is very complicated at the commercial level, with all kinds of processes and additions, but you can make very tasty wine by simply crushing grapes and allowing the native microbes to ferment the sugars into alcohol. You don’t need to be an expert or a microbiologist to make tasty homemade wine, beer, or mead, but having a basic understanding of the science behind the process will give you a better chance for success.

The catalyst for alcohol fermentation is yeast, and the yeast specifically responsible for all these fermented beverages is Saccharomyces cerevisiae. This species is widely used by humans for alcohol and bread fermentation, and within this species there are literally hundreds of different strains for the home brewer to choose from.

It should be noted that while the alcohol fermentation will benefit from having some oxygen present in the initial phase, in the form of dissolved oxygen in the must (the liquid mixture prior to fermentation), the process should otherwise be carried out anaerobically in a sealed carboy. It could be said that the art of making alcohol is the art of not making vinegar. Acetobacter (the bacteria responsible for producing vinegar) is essentially everywhere: in the air, on the skins of fruit, and, if you use raw vinegar in your kitchen, most definitely there. If this bacteria infiltrates your hooch, it will turn it into vinegar. Vinegar is easy to make for this reason, whereas alcohol requires more care and vigilance.

Okay, now that you’ve been warned about the perils of Acetobacter, let’s begin. Alcohol fermentation has three main phases:

  • The lag or adaptation phase
  • The primary fermentation phase
  • The secondary fermentation or conditioning phase

In an optimal fermentation where the yeast population is significant, the nutrition is adequate, and the sugar content and temperature are within the yeast’s optimal range, the yeast should be able to move through all these stages in two to three weeks.

Large fermentation metal cauldron hanging from chains

The exact ingredients and quantities will vary by type of beverage, but generally speaking, alcohol fermentation begins as soon as a sugar source is combined with water, creating what is called the must (an unfermented water and sugar solution), and the must is then exposed to the catalyst for the yeast fermentation, Saccharomyces, which is either added or naturally present in the must.

The lag phase, also called the adaption phase is essentially the period where the yeasts are acclimating to their new environment (temperature, nutrients, pH, and sugar level) and preparing for reproduction by strengthening their cell walls and accumulating nutrients that will be needed to reproduce and proliferate. Once the yeast cells have acclimated to their new environment, they begin their asexual reproduction. The cells form a bud in their cell walls, which eventually becomes a new yeast cell. Producing this new cell requires the yeast to utilize oxygen, nitrogen, and other nutrients, consuming all of them at a rapid rate. This phase is sometimes called the “respiratory” or “aerobic” phase because the yeast cells benefit from oxygen, which is dissolved into the must, in order to reproduce rapidly. The yeast can take other metabolic pathways to grow and reproduce in the absence of dissolved oxygen, but they can do so much more efficiently and rapidly with an adequate amount of dissolved oxygen in the must. For this reason, most experienced brewers utilize some method for getting oxygen dissolved into the must, as having enough dissolved oxygen will enable the yeast to acclimate and reproduce more rapidly and effectively, which in turn will ensure a good fermentation. This is the reason our alcohol recipes call for both the agitation of the must prior to fermentation, which incorporates oxygen into the liquid, as well as using a yeast nutrient, which supplies the yeast with much-needed nitrogen and other nutrients. Alcohol is often fermented in an open-top fermenter up through the first three to five days to allow oxygen from the air to be diffused into the must. Winemakers employ this strategy, and you can as well, provided that you cover the fermenting must with a porous cloth such as cheesecloth. The fruit also contributes nutrients to the fermenting must, as well as other beneficial sensory-enhancing characteristics such as tannins and flavor compounds. This will ensure that you get a steady supply of oxygen and nutrients through this crucial stage. Make sure that the porous cloth is not so porous that flies can get through it, as they are attracted to alcohol and carry Acetobacter (which, as you know, will turn your hooch into vinegar!). If flies are a problem, you can hang some fly strips nearby to keep them at bay. After fermenting with the fruit, the must is then strained off the fruit and transferred by siphon (to limit oxidization and exposure to Acetobacter) into a carboy fitted with an airlock to facilitate an anaerobic environment. If you don’t know about smoking meat than you may read more about smoking meat.

The primary fermentation phase occurs in an anaerobic environment, as most of the oxygen was utilized during the previous stage and the yeast switch metabolic pathways. At this juncture, the yeasts shift their focus from reproduction to fermentation. Using enzymes, the yeast first breaks down complex sugar molecules (disaccharides) into simple sugar molecules (glucose). Then the yeast can begin to rapidly digest and metabolize the glucose. For every molecule of glucose digested, the yeast produce two ethanol molecules and two carbon dioxide molecules. This fermentation phase usually begins within two or three days of the initiation of the ferment and can be characterized by the vigorous fermentation action, visible to the naked eye as bubbling and foaming, as well as lots of bubbles and “blurps” coming from the airlock. At this point, if all has gone according to plan, the yeast rapidly consume the sugars and produce loads of alcohol and carbon dioxide. This vigorous fermentation will continue, as long as the yeast culture is healthy and well fed, until all the available sugars in the must have been converted or the yeast hits the point of its own alcohol tolerance. Once all the sugars have been digested, the yeasts begin to significantly slow down, becoming less and less active as they head into the final phase of fermentation. This can be visually detected by the slowing and eventual stopping of the bubbling in an airlock, as well as the settling of the dead yeast cells at the bottom of the fermentation vessel. A hydrometer is used to assess how much sugar remains and to determine when to bottle.

In the secondary fermentation phase, all or nearly all the sugar has been converted to alcohol, or the yeast strain has reached its tolerance level for alcohol, and the yeast cells start to die off or prepare for dormancy. The dead and dormant yeast cells begin to sink to the bottom of the fermentation vessel and form flocs, which are clumps of dead or dormant yeast cells that eventually form a unified layer at the bottom of the vessel. A yeast’s ability to flocculate is predetermined by its genetics, and how well a yeast strain flocculates, meaning how quickly and compactly it settles to the bottom of the fermenter, is one of the aspects that producers use to judge a yeast’s viability. The vigorous fermentation phase is over at this point; most of the sugars have been digested and the majority of yeast cells have died off or gone dormant, but some of the yeast cells are still active, and they continue to metabolize the remaining fermentables. These remaining yeasts continue the fermentation at a slow pace as they digest heavier sugars and even some by-products that were produced during the primary fermentation phase. The fermentation continues until the fermentable products are mostly digested, the yeast continually slowing over time. Allowing for a total fermentation time of three to four weeks should provide enough time for these secondary fermentation reactions to occur, although temperature will be a defining variable in determining fermentation time.

Close-up of a glass jar with a sealed lid filled with jam or preserves

At this point in the process, fermentation is pretty much complete, and all that’s left to do is bottle and age (condition) your fermented alcoholic beverage (or drink immediately, if you so choose). Bottle aging (conditioning) improves the quality of most alcoholic beverages, as the slow fermentation still persists in the bottle and continues to alter the beverage, often mellowing and improving the flavor over time. Meads really benefits from an extended conditioning period and we recommend that you age meads for at least six months before drinking (three months absolute minimum if you are dying to get at it!). Racking, the process of using a siphon and a racking cane to transfer the fermented liquid from one vessel to another or into bottles, will help clarify the beverage and result in a less yeasty flavor. The more yeast cells that end up in the bottle, the more yeasty flavor will come through in the finished beverage. You can rack straight into the bottle and forgo the many racking steps that many home brewers suggest are necessary if you don’t mind having some of the dead yeast bodies in your finished beverage—they’re full of protein and nutrients. Also, if you are careful when bottling, you can get most of the liquid out and leave behind most of the floc, yielding quite a clear beverage. Salt curing is the very important to cure foods easily in this time, learn more about salt curing.

If you want a sparkling finished beverage, you can prime the bottles (meaning that you add a small amount of sugar to the bottles giving the microbes the food they need to produce additional CO2), seal the bottles, and allow for a conditioning period in the bottle. This should be decided before you start the process, as the quantity of sugar, the strain of yeast, and the desired alcohol content all play into the original equation. Sometimes, if the yeast cells are no longer active in your beverage, you may need to add additional yeast to the bottles for a successful secondary fermentation in the bottle (most often, though, this isn’t necessary).

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