Second fermentation (F2) is the key to creating that delightful fizz in your kombucha, and choosing the right bottles and caps is crucial for success. In this guide, we’ll walk through the best options for bottles, what to avoid and why caps are just as important as the bottles themselves. 

What to Look For in F2 Bottles 

When selecting bottles for F2, prioritise good-quality, food-grade glass that is thick enough to handle the pressure created during carbonation. You’ll also need a cap that forms a tight, airtight seal to trap the carbonation in the liquid. This will ensure that your kombucha becomes fizzy while it ferments in the bottle. 

What to Avoid 

Using poor-quality or thin glass can be dangerous during second fermentation. As carbonation builds, the pressure in the bottle increases, which could lead to a bottle explosion if the glass isn’t strong enough. Here’s what to steer clear of: 

Decorative or coloured glass not designed to hold liquids. 

Flip-top bottles from IKEA, as they may not form a proper seal. 

Square-shaped bottles, which are more prone to cracking or exploding under pressure. 

Recycled beer bottles (details below). 

Best Bottle Options for Second Fermentation 

1. Flip-Top Bottles 

Flip-top bottles are extremely popular among home brewers because they create a very tight seal. These bottles are made of thick glass and are perfect for trapping carbonation. They can be a little pricey, and the tops can be stiff initially, but once broken in, they are great for consistent results. 

2. Specialty Bottles 

If you’re brewing large quantities of kombucha, specialty bottles are another great option. These come in various sizes (8 oz., 16 oz., etc.) and shapes, allowing you to choose what suits your needs. They’re less bulky than flip-top bottles and can be bought in bulk from wholesale bottle suppliers for a lower cost. 

The Importance of Bottle Caps 

The cap is just as critical as the bottle itself. A proper cap will ensure that your bottles stay sealed tightly, trapping the carbon dioxide inside for carbonation. Here are two of the best types of caps to use: 

1. Polycone Seal Caps 

Polycone caps have a conical liner on the inside, which is designed to make a very tight seal. While they are often touted as the best option for holding carbonation, they can be more expensive. In my experience, these work well, but the price difference doesn’t justify the minimal improvement over F217 caps. 

2. F217 Caps 

F217 caps are basic black caps with a white foam liner inside. These caps are affordable and highly effective at trapping carbonation. They’re my favourite choice because they are reliable, inexpensive and easy to find. Plus, once your kombucha is carbonated, the caps will become slightly convex, giving you a visual cue that they’re ready to refrigerate. 

Iffy Options for F2 Bottles 

1. Beer Bottles 

While beer bottles are readily available and affordable, they aren’t the best option for second fermentation. Thin glass beer bottles can break under pressure, especially if left at room temperature for more than a day. If you must use them, move the kombucha to the fridge quickly to avoid any risk of breakage. 

2. Mason Jars 

Mason jars are another iffy option. Although they are easy to find, they are unreliable for building consistent carbonation. The seal isn’t tight enough, often leading to flat kombucha. 

Dark vs. Clear Glass 

When it comes to choosing between dark and clear glass, it’s mostly a matter of preference. If your bottles will be exposed to sunlight, opt for dark glass to avoid any anti-microbial effects from the sun, which could slow or halt fermentation. If you store your kombucha in a dark cupboard (which is ideal), clear glass is perfectly fine and allows you to monitor the carbonation more easily. 

Conclusion 

Choosing the right bottles and caps for second fermentation is essential for building great carbonation and ensuring the safety of your brew. High-quality, food-grade glass with airtight seals is the key to creating fizzy, flavourful kombucha. Whether you opt for flip-top bottles, recycled store-bought bottles, or specialty bottles, make sure to prioritise thick glass and secure caps to get the best results!