In today’s post, we take a closer look at fermenters and the fermentation process itself. We’ll share several practical tips on how to run this crucial stage so your wash ferments smoothly and without unnecessary complications.

Let’s start with the basics—what exactly is fermentation? It is a process in which yeast converts sugars into ethyl alcohol and carbon dioxide. Put simply, yeast “eats” sugar and “exhales” alcohol and CO₂. This is a fundamental stage of home alcohol production, largely determining both yield and the final quality of your spirit. It’s important to remember that yeast are living organisms—they need proper conditions to work efficiently: nutrients (sugar), minerals, the right temperature, and at the beginning, also oxygen.

At the start of fermentation, the presence of oxygen in the wash is actually desirable. Oxygenating a freshly prepared wash (e.g., vigorous stirring or pouring the sugar solution from a height) helps the yeast multiply quickly and build a strong population. The more healthy yeast cells begin working, the more efficiently the vigorous fermentation will proceed. However, as soon as fermentation takes off, oxygen supply must be reduced to the absolute minimum. In practice, this means sealing the fermenter and leaving as little headspace as possible above the liquid. The less air above the wash, the lower the risk of oxidation. After just a dozen hours or so, yeast will produce a layer of CO₂ that “blankets” the wash, pushing nearly all oxygen out of the container. This CO₂ cushion protects the mash from unwanted microorganisms—such as acetic bacteria or mold, which require oxygen to grow. That’s why once fermentation is underway, you should avoid frequently opening the fermenter or stirring the wash. Every unnecessary lid opening introduces oxygen, which can slow down yeast (a phenomenon known as the Pasteur effect) and increase the risk of contamination.

The standard image of a fermenter includes a container fitted with an airlock filled with water. This simple tool allows the CO₂ produced during fermentation to escape while preventing ambient air from entering. It works perfectly for washes that ferment in a relatively calm manner—such as wine or beer, where gas release is moderate. However, with very vigorous fermentations (as with sugar washes on turbo yeast), the airlock may not be able to release gas quickly enough. Large volumes of CO₂ and foam can fill and clog the airlock, causing pressure inside the fermenter to rise dangerously. In extreme cases, the lid may pop off, and the fermenter may “explode”—creating a spectacular mess (and losing valuable wash). To prevent this, many experienced distillers avoid using an airlock during the most active stage of sugar-wash fermentation. Instead, the lid is left loosely in place (not snapped shut), and in the case of glass carboys, the opening may simply be covered with clean gauze rather than a cork and airlock. The idea is to allow CO₂ to escape freely through any gaps without building excessive pressure. This “open” fermentation method is used only during the first, most active days. Once fermentation calms down, you can seal the fermenter more tightly or install an airlock for the remainder of the fermentation—especially for washes that require longer aging.

Temperature is another crucial factor. Yeast works best within a specific range—typically 20–28°C for strains used in home brewing and distilling. If the environment is too cool, yeast will ferment sluggishly (or stop entirely), while excessive heat promotes off-flavors and can weaken or kill the yeast. It’s therefore important to keep the fermenter in a place with a stable, appropriate temperature. Remember that fermentation is exothermic—meaning it generates heat—so the wash is often several degrees warmer than the room. If the wash gets too warm, move it somewhere cooler. If too cold, insulate the fermenter (e.g., wrap it in a blanket or use a heating belt). Never try heating the wash with an immersion heater! Beginners sometimes use aquarium heaters to maintain 25°C in a cold garage. Unfortunately, this often ruins the wash—the surface of such heaters becomes extremely hot, instantly killing any yeast that come into contact with it. The wash heats unevenly, part of the yeast dies, and fermentation may stop altogether. It is far safer to heat the fermenter from the outside or warm the room instead.

Now let’s compare different types of fermenters. You can choose from glass, stainless steel, and the most common—plastic. Let’s start with plastic, as it is the most widespread option in home fermentation. Plastic fermenting buckets of 20–30 liters are cheap, lightweight, and very convenient. Their wide opening makes it easy to add sugar, fruit, or other ingredients, and also to clean them afterward. A bucket with a lid (with a gasket and optionally an airlock) is basic equipment found in every home brewing store. Larger plastic barrels (50, 100 liters, or more) are also available for those who ferment in bigger quantities. Plastic has many advantages—it doesn’t react with the wash, doesn’t rust, and is easy to handle. But it also has drawbacks: the material is relatively soft and prone to scratches, and over time it may absorb odors and stains. Plastic is also not completely gas-tight—small amounts of oxygen can slowly permeate through the walls. With long fermentations (lasting months), this may negatively affect flavor. Despite these limitations, for short fermentations (such as 1–2 week sugar washes), plastic fermenters work exceptionally well.

Another option is the classic glass fermenter—the carboy (demijohn). Many people still use them for wine, mead, or liqueur fermentation. Glass offers a major benefit: it is completely chemically inert—it does not affect the flavor or aroma of the wash, does not absorb oxygen, and does not retain odors. Glass fermenters also clean easily—you can even rinse them with boiling water (which you cannot do with plastic). However, glass fermenters also have downsides. They are heavy and fragile—one drop or strong impact may shatter the vessel (and the wash will be lost). Their narrow neck makes it difficult to add ingredients and clean the inside. Removing fruit pulp or yeast sediment through such an opening can be challenging. If you ferment something that produces a lot of foam or contains solids (fruit pieces, grain), the foam may clog the narrow neck, and vigorous fermentation can force the wash out. For this reason, buckets or barrels are more commonly used for fermentations with solids, while glass carboys are preferred for clear juices, wines without pulp, or secondary fermentation after racking.

More advanced setups include stainless steel fermenters, often with a conical design. Stainless steel is an ideal material—it withstands nearly anything, does not react with the wash, does not absorb smells, and will last for years. The conical bottom allows yeast sediment to collect in one place and be removed through a bottom valve without disturbing the clear liquid above. Many stainless fermenters come with useful features such as sampling valves, sight glasses, thermometer ports, or even cooling jackets. The only drawbacks are their high cost and weight.

A good compromise between basic and professional fermentation gear is the modern high-quality plastic fermenter, such as FermZilla. These are made from thick PET plastic shaped into a conical form. They also allow yeast harvesting and fermentation similar to stainless steel conicals. FermZilla is transparent, allowing you to observe fermentation without opening the lid. Some models are rated for fermentation under slight pressure—a popular technique in homebrewing, allowing oxygen-free secondary fermentation and CO₂-assisted bottling. They are lighter and cheaper than stainless steel but offer many similar features (such as easy yeast collection). However, they require careful handling—while durable, the plastic can crack or scratch if mishandled. And as with all plastic, long-term durability cannot match stainless steel—gaskets, valves, and seals will eventually wear out, and the vessel may need replacement after a few years of heavy use.

Finally, a few universal words on sanitation. No matter which type of fermenter you use, it must be thoroughly cleaned and sanitized after each fermentation. Residual yeast, pulp, or sediment must never be left behind—this is an easy path to infection. The rule when cleaning is: clean effectively, but gently. Never use abrasive scrubbers or wire brushes, as they damage the surface of the vessel. Plastic, in particular, scratches easily, and scratches become breeding grounds for bacteria and wild yeast that resist normal sanitizers. The best method is washing immediately after transferring the wash—using warm water and a mild, unscented detergent. Stubborn deposits should be soaked before removal with the soft side of a sponge. It is also a good idea to apply a sanitizing agent (e.g., potassium metabisulfite or an oxygen-based sanitizer) according to the manufacturer’s instructions. After washing, the fermenter should be dried and stored closed so it does not collect dust.

Keep in mind that plastic fermenters have a limited lifespan. Even with excellent care, after several cycles small micro-scratches appear that are invisible to the eye, and the material may permanently absorb the smell of previous washes. In practice, many experts recommend replacing a plastic bucket or barrel after around 5–6 fermentations (or after about half a year of use). This ensures that each new wash ferments in a clean vessel without the “baggage” of previous batches. Glass carboys and stainless steel tanks, on the other hand, last much longer—usually only gaskets need replacement, while the glass or steel itself can withstand dozens of fermentations, as long as the carboy isn’t dropped.

As we can see, a fermenter is not just a simple container—it is the small kingdom of your yeast. Treat it well, and it will reward you with a successful fermentation and a delicious homemade spirit. Good luck, and cheers!