Fermenter King Junior 20L: Setup, Brew Day Steps and Tips for Homebrewers

By Caleb Morgan

Updated November 2026

A fermenter king junior 20l is a compact, budget-friendly vessel that lets you ferment a full batch of beer, wine or kombucha without committing to a large carboy or bucket. This guide walks you through choosing the right setup, preparing the fermenter before brew day, filling and pitching yeast, managing fermentation, and racking or bottling at the end. By the time you finish, you will have a repeatable process you can run in a small kitchen or garage.

What the Fermenter King Junior 20L Is Built For

The fermenter king junior 20l is sized for roughly five gallons of finished liquid, which is the standard homebrew batch. That size suits most extract kits, partial mash recipes and small all-grain brews. Because the working volume is limited, you need to leave headspace for foam, usually at least a third of the vessel during active fermentation. For a 20-liter unit, that means you should aim for a batch of about 15 to 17 liters at the start, not a full 20.

Shopping for one? See our guide: FastFerment Conical Fermenter 7.9 Gallon Review (2026).

Most people who buy a fermenter in this size range do so because it fits under a counter or on a shelf, and it is easy to lift when full. Keep in mind that a full 20-liter fermenter is heavy. Plan your transfers so you are not carrying a full vessel up stairs or across a slippery floor.

What You Need Before Your First Brew Day

Before you fill the fermenter, gather the equipment that touches your beer after the boil. Sanitation is the step most likely to make or break a batch, so have everything ready.

• Fermenter lid with airlock or bung (check that the grommet fits snugly)
• Airlock, filled to the marked line with water or sanitizer
• Sanitizer rated for homebrewing (no-rinse types are common)
• Thermometer that reads wort temperature accurately
• Hydrometer and sample jar or tube
• Auto-siphon or racking cane with tubing
• Large spoon or paddle, sanitized
• Yeast, pitched at the correct rate for your gravity
• Blowoff tube, if your recipe is likely to foam heavily

Step 1: Clean and Sanitize the Fermenter

Start by washing the vessel with warm water and a mild cleaner. Rinse thoroughly to remove soap residue, since soap can suppress yeast. Next, sanitize all surfaces that will contact the wort. Fill the fermenter with the diluted sanitizer solution, put the lid on, and swirl so the solution reaches the inside of the lid and the spout. Let it sit for the contact time listed on the label, then drain. If you use a no-rinse sanitizer, do not rinse afterward, or you will reintroduce contaminants.

Sub-steps for a clean seal

1. Inspect the lid gasket for cracks. Replace it if you see any.
2. Wet the grommet and insert the airlock. Confirm it sits flush.
3. Fill the airlock to the line with sanitizer solution or water.
4. Set the assembled lid aside, keeping it covered.

Step 2: Transfer and Chill the Wort

Once the boil is complete, cool the wort as quickly as you can. Rapid cooling reduces the window for bacteria and helps create a clean cold break. Many brewers use an immersion chiller, a plate chiller or an ice bath. Aim to bring the wort down to your yeast’s recommended pitching temperature, which is often in the upper 60s Fahrenheit for many ale strains and lower for lagers.

When the wort is cool, transfer it into the fermenter. Pour gently to limit splashing, which picks up oxygen. Oxygen is useful before pitching yeast because it supports yeast growth, but it becomes a problem once fermentation begins. Top the fermenter up with cold, sanitized water to reach your target batch volume of about 15 to 17 liters, leaving headspace for krausen.

Step 3: Take a Gravity Reading and Pitch Yeast

Use your hydrometer to record the original gravity. Take the reading after the wort is well mixed and at the temperature the hydrometer is calibrated for, usually around 60°F (15.5°C). Write it down. You will need it to calculate alcohol content later.

Next, pitch the yeast. Dry yeast can often be sprinkled directly onto the wort after rehydration instructions are followed. Liquid yeast should be added according to its package guidance. Seal the lid, and make sure the airlock is bubbling within 24 to 48 hours in most typical setups.

Step 4: Manage Fermentation in the Fermenter

Fermentation is where the fermenter king junior 20l earns its place. Keep it in a spot with a stable temperature, away from direct sunlight and drafts. Small temperature swings can cause off-flavors, so a closet, basement or insulated cabinet often works well. If you ferment in a warm room, consider a fermentation chamber or a water bath to hold a steady temperature.

Expect a thick layer of foam, called krausen, during the first few days. Because the batch is near the top of the 20-liter capacity, use a blowoff tube if you see foam reaching the lid. Do not let the airlock become clogged with krausen, or pressure can build up. Check your fermenter daily for the first several days, then less often as activity slows.

Checking for completion

Fermentation is usually considered complete when the gravity reading stays the same over two or three consecutive days. Take a sample with a sanitized tube, cool it, and read the hydrometer. Compare the final gravity against the original gravity to estimate alcohol content and confirm that the beer is finished.

Step 5: Rack, Clean Up and Package

When fermentation is complete, you will usually transfer the beer off the yeast cake. Use a racking arm or auto-siphon so you do not stir up sediment, which can add off-flavors. Keep the outlet of the siphon near the bottom of the fermenter but above the trub layer. Move the beer into a clean, sanitized bottling bucket or keg.

After transferring, rinse the fermenter promptly with warm water to prevent residue from drying onto the walls. Wait until the next brew day to sanitize again.

Common mistakes

• Filling to the brim. Leave room for krausen. A full 20-liter fermenter often overflows.
• Using dirty equipment. Sanitize everything that touches cooled wort, including the spoon and siphon tubing.
• Skipping the gravity reading. Without an original gravity, you cannot judge fermentation or alcohol content.
• Opening the lid too often. Every opening raises contamination risk and can cause temperature shifts.
• Racking too early. Move the beer only after the gravity has stabilized, or you may get bottle bombs or a stuck fermentation.
• Letting the airlock run dry. Top it up with sanitizer solution if the liquid evaporates.

Tips for Getting Consistent Results

• Label each batch with the date, recipe and original gravity.
• Keep a brew log so you can compare results across batches.
• Store the fermenter on a stable surface, especially when full.
• Use a separate sanitizer container so you do not cross-contaminate tools.
• If you ferment a lager-style beer, plan for a cold, controlled environment, since the yeast needs it.

Recommended gear

A blowoff tube is useful because the batch size is close to the vessel’s limit, and foam can overflow quickly. View on Amazon

A digital thermometer with a probe helps you confirm wort temperature before pitching and during fermentation. View on Amazon

An auto-siphon makes racking cleaner, because it starts flow without mouth suction and helps you avoid disturbing sediment. View on Amazon

A no-rinse sanitizer simplifies cleanup and reduces the number of steps where contamination can occur. View on Amazon

For more background on fermenter types and setup, see What Is the Main Function of Fermenter? A Homebrewer's Guide (2026) and Plastic vs Glass Fermenter: Which Is Better for Your Brews?. If you plan to use a conical design later, Using a Conical Fermenter: A Step-by-Step Guide for Homebrewers covers that workflow. For troubleshooting surface problems during fermentation, see White Film on Beer in Fermenter: What It Is and How to Fix It. Racking tips are also covered in Racking Arm for Fermenter: How to Siphon Beer Without Stirring Up Sediment.

FAQ

What batch size works best in a fermenter king junior 20l?

Most brewers fill it to about 15 to 17 liters. This leaves room for foam during active fermentation and reduces the chance of overflow.

Do I need a blowoff tube with this fermenter?

Not always, but it is a good idea for vigorous ales or high-gravity recipes. A blowoff tube routes foam into a container so it does not clog the airlock.

How long should I ferment in this vessel?

Many ales finish in one to two weeks, while lagers and high-gravity beers can take longer. Base your decision on stable gravity readings rather than a fixed day count.

Can I use it for wine or kombucha?

Yes, many homebrewers use similar vessels for wine and kombucha. Check the material and seal for compatibility with acidic liquids and always sanitize thoroughly.

How do I know when fermentation is finished?

Take two or three gravity readings a day apart. If the reading stays the same, fermentation has likely stopped and the beer is ready to package.

Should I rinse after using sanitizer?

It depends on the product. Follow the label. No-rinse sanitizers should not be rinsed, while others may require a thorough rinse with clean water.

What temperature is ideal for fermentation?

It depends on the yeast strain. Check the manufacturer’s recommended range and keep the temperature as steady as possible throughout fermentation.

Conclusion

A fermenter king junior 20l gives you a practical, space-saving way to brew five-gallon-style batches at home. Sanitize carefully, leave headspace for foam, track gravity readings, and rack gently at the end. With a consistent routine and a simple brew log, you can improve your results with every batch.

About Caleb Morgan

Caleb Morgan is part of our editorial team and reviews and edits our home brewing guides, checking product details against manufacturer specifications and owner feedback.