Carboys and Demijohns: Glass vs. Plastic Guide

Understanding Carboys and Demijohns

Carboys and demijohns are narrow-necked containers used primarily for secondary fermentation and aging in home winemaking. While the terms are sometimes used interchangeably, there are subtle differences. A carboy typically refers to a large bottle with a narrow neck, available in glass or plastic, and commonly found in 3-gallon, 5-gallon, and 6.5-gallon sizes. A demijohn traditionally refers to a large glass bottle, often encased in a wicker basket, with capacities ranging from 1 gallon to 15 gallons or more.

Both serve the same fundamental purpose: providing a sealed environment where wine can undergo secondary fermentation, clarification, and aging with minimal oxygen exposure. The narrow neck is key, as it limits the surface area exposed to air and makes it easy to seal with a bung and airlock.

For home winemakers, carboys and demijohns are indispensable. They allow you to observe the wine's progress, monitor clarity, and detect any issues such as renewed fermentation or sediment buildup without disturbing the wine itself.

A Brief History

The word "carboy" derives from the Persian word "qarabah," meaning a large flagon. These vessels have been used for centuries to transport and store liquids. In winemaking, glass carboys became the standard for home production in the mid-20th century and remain enormously popular today. Demijohns with wicker casings were common throughout Europe and are still widely used in Mediterranean winemaking traditions.

Glass Carboys: Pros and Cons

Advantages of Glass

Glass carboys are favored by serious home winemakers for several compelling reasons. Glass is completely non-porous, meaning it will not absorb colors, odors, or flavors from previous batches. This makes glass easy to sanitize to a truly clean state every time. Glass is also impermeable to oxygen, which is critical during extended aging periods when even tiny amounts of oxygen ingress can cause oxidation and spoilage.

The transparency of glass allows you to monitor your wine's color, clarity, and sediment levels without opening the vessel. You can watch fermentation activity, observe fining agents at work, and determine when the wine is ready to bottle simply by looking at it.

Glass is also chemically inert, meaning it will not react with the acids, alcohol, or sulfites in your wine. This ensures that the vessel itself contributes no off-flavors or contaminants to the finished product.

Disadvantages of Glass

The most significant drawback of glass carboys is their weight and fragility. A standard 6-gallon glass carboy weighs approximately 12 pounds empty and over 55 pounds when full of wine. Moving a full glass carboy requires care and ideally a carboy handle or brew hauler strap. Dropping a full glass carboy is not only costly but genuinely dangerous, as the combination of broken glass and 6 gallons of liquid creates a serious hazard.

Glass carboys can also be challenging to clean, particularly if sediment has dried inside. The narrow neck limits access, so a carboy brush or specialized cleaning equipment is often necessary. Despite these drawbacks, many winemakers consider glass the gold standard for secondary fermentation and aging.

Price range: $25 to $55 depending on size and source.

Plastic Carboys: Pros and Cons

Advantages of Plastic (PET)

Modern PET (polyethylene terephthalate) carboys have addressed many of the traditional concerns about plastic in winemaking. PET is significantly lighter than glass, making transport and handling much easier, especially for larger volumes. A 6-gallon PET carboy weighs only about 2 pounds empty compared to 12 pounds for glass.

PET carboys are also virtually unbreakable. They can be dropped without shattering, making them safer for use in garages, basements, and other spaces where accidents are more likely. This durability also makes them excellent for outdoor winemaking events and classes.

Many PET carboys now feature wide mouths that make filling and cleaning dramatically easier than traditional narrow-neck designs. Some models include graduated markings for volume measurement, which is convenient when topping off or calculating additions.

Disadvantages of Plastic

The primary concern with plastic carboys is oxygen permeability. While PET is far less permeable than older plastics, it does allow slightly more oxygen transfer than glass over extended periods. For wines aged less than six months, this difference is negligible. For long-term aging of a year or more, glass or stainless steel is the better choice.

Plastic can also develop micro-scratches over time, particularly from cleaning brushes and rough handling. These scratches can harbor bacteria and become increasingly difficult to sanitize. For this reason, many winemakers replace PET carboys every three to five years.

Some winemakers also report that certain plastic carboys develop a slight static charge that attracts dust and makes them harder to keep visually clean on the outside.

Price range: $15 to $35 depending on size and design.

Better Plastic (BPA-Free and Tritan)

Newer carboy designs use Tritan copolyester or other BPA-free plastics that offer improved clarity, scratch resistance, and reduced oxygen permeability compared to standard PET. These premium plastic carboys bridge the gap between traditional PET and glass, offering many of the visual benefits of glass with the practical advantages of plastic.

Price range: $25 to $45 for Tritan models.

Choosing the Right Size

Small Carboys (1 to 3 Gallons)

Small carboys are ideal for experimental batches, topping off larger carboys, and making country or fruit wines in limited quantities. A 1-gallon glass jug is one of the most useful items in any winemaker's collection, as it serves double duty for small batches and as a source of topping wine for larger vessels. Three-gallon carboys are perfect for winemakers who want to make multiple varieties without committing to large volumes of each.

Standard Carboys (5 to 6.5 Gallons)

The 5-gallon and 6-gallon carboy are the workhorses of home winemaking. Most recipes and wine kits are designed for these sizes, and the vast majority of winemaking accessories (bungs, airlocks, brushes, and carriers) are made to fit them. A 6-gallon carboy holds approximately 30 standard 750ml bottles of wine, making it a practical batch size for personal consumption and sharing.

Large Demijohns (10 to 15 Gallons)

Large demijohns are used by winemakers who produce bigger batches or prefer to ferment and age in a single large vessel before splitting into smaller containers for finishing. Italian-style glass demijohns in 14-gallon (54-liter) sizes are popular among winemakers of Italian heritage and those who process larger quantities of fresh grapes. These oversized vessels require sturdy stands and careful handling due to their considerable weight when full.

Price range for large demijohns: $40 to $120 depending on size and source.

How to Use Carboys and Demijohns

Setting Up for Secondary Fermentation

After primary fermentation is complete (typically 5 to 7 days for most wines), rack the wine from the primary fermenter into a clean, sanitized carboy using a siphon. Fill the carboy to within an inch or two of where the bung will sit, minimizing the headspace. Insert a sanitized bung fitted with a three-piece or S-shaped airlock filled with sanitizer solution or clean water.

Place the carboy in a location with a stable temperature between 60 and 70 degrees Fahrenheit, away from direct sunlight. Sunlight can degrade wine quality and promote unwanted chemical reactions, particularly in white wines.

Topping Off

As sediment settles and you rack the wine, the volume decreases slightly each time. Topping off means adding wine (ideally the same variety or a neutral wine) to fill the carboy back to the neck, eliminating excess headspace. Keep a 1-gallon jug of the same wine specifically for this purpose.

Racking from Carboy to Carboy

Most wines benefit from two to three rackings during secondary fermentation and aging. Each racking separates the clear wine from the sediment (lees) that accumulates at the bottom. Use an auto-siphon and food-grade tubing, being careful not to disturb the sediment layer. Position the racking cane about an inch above the lees for the cleanest transfer.

Cleaning and Maintenance

Cleaning Glass Carboys

Immediately after emptying, rinse the carboy with warm water to remove loose sediment. Fill with a solution of PBW (Powdered Brewery Wash) or a similar oxygen-based cleaner and let it soak for 30 minutes to several hours for stubborn deposits. Use a carboy brush with soft bristles to scrub the interior, paying special attention to the shoulder area where residue tends to collect. Rinse thoroughly with clean water.

For extremely stubborn stains or deposits, a handful of uncooked rice with warm water and a small amount of cleaner can be swirled inside the carboy as a gentle abrasive.

Cleaning Plastic Carboys

Use the same cleaning solutions as for glass, but avoid abrasive brushes or pads that could scratch the surface. Soft cloths, sponges, or dedicated non-scratch carboy brushes are best. Soaking is your primary cleaning method with plastic, as the smooth surface releases most residues with chemical action alone.

Sanitizing Before Use

After cleaning, sanitize with a no-rinse sanitizer such as Star San or an iodophor solution. Swirl the sanitizer to coat all interior surfaces and allow proper contact time as directed on the product label. Drain but do not rinse, as the residual sanitizer at proper dilution is safe and effective.

Storage Tips

Store carboys upside down on a drying rack or right-side up with a loose cover of aluminum foil or a paper towel over the opening. Never seal a damp carboy tightly, as trapped moisture promotes mold growth. Keep glass carboys in protective cases or padded areas where they won't be knocked over.

Frequently Asked Questions

What is the difference between a carboy and a demijohn?

The terms overlap significantly. Carboy generally refers to any large narrow-necked bottle used for fermentation, available in glass or plastic. Demijohn traditionally refers to a large glass bottle, often with a wicker or plastic protective casing, and is more common in European winemaking terminology.

How long can I age wine in a plastic carboy?

For best results, limit aging in a PET carboy to six months or less. For longer aging, transfer to glass or stainless steel to minimize the risk of oxidation through the slightly oxygen-permeable plastic.

Do I need a carboy handle or carrier?

A carboy handle or brew hauler is strongly recommended for glass carboys, especially when full. These inexpensive accessories dramatically reduce the risk of dropping and breaking a heavy, slippery carboy. They typically cost $5 to $15 and are well worth the investment.

Can I use a carboy for primary fermentation?

While possible for white wines and juices (which don't require cap management), carboys are not ideal for primary fermentation. The narrow neck makes it difficult to add and remove fruit, and vigorous fermentation can clog the opening or blow out the airlock. Use a wide-mouth bucket or fermenter for primary fermentation instead.

How do I remove stubborn stains from a glass carboy?

Soak with PBW or OxiClean Free overnight. For persistent stains, use a combination of warm water, uncooked rice, and cleaner as a gentle abrasive scrub. Barkeeper's Friend (oxalic acid-based cleaner) can also be effective for mineral deposits and stubborn discoloration.

Should I buy one large carboy or several small ones?

Both have advantages. One large carboy simplifies the process for single-batch winemakers. Multiple smaller carboys offer flexibility to make different wines simultaneously, experiment with different treatments (oaked vs. unoaked, for example), and provide topping wine. Most winemakers eventually accumulate a collection of both sizes.

How many carboys do I need to get started?

At minimum, you need one carboy for secondary fermentation and ideally one or two 1-gallon jugs for topping off. As your winemaking progresses, a second full-size carboy becomes essential for racking wine from one vessel to another without reusing the same container before it has been cleaned.

Are colored glass carboys better than clear ones?

Colored glass (amber or green) provides some UV protection, which can benefit wines aged for extended periods in areas with ambient light. However, if you store your carboys in a dark location, clear glass works perfectly well and has the advantage of allowing you to see the wine's true color during aging.