Corking

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Corking refers to closing a bottle with corks (either synthetic or natural). This page focuses on why and how to cork a beer. For information on other package types and general guidelines on when and how to package your beer see the Packaging page. See Floor Corker for more information on floor corker products.

Why choose to cork bottles?

Deciding between corks and other closures such as caps will depend on the specific beer and the brewer's goals with the beer. Caps are a cheaper closure and are also easier to apply. Aside from aesthetics, you may choose corks when intending to age or store beers lying down in order to keep the beer from interacting with the cap. Some producers have observed that crown caps contribute to an off-flavor in their beer, especially if the beer is acidic. Pierre Tilquin closes some bottles of every blend with crown caps in order to test carbonation levels. He has noticed that the crown capped bottles have an off flavor not present in the corked bottles [1]. Other producers regularly package their acidic beer with crown caps (e.g. the Rare Barrel, Boon Geuze in 25 cl bottles) and have not mentioned a problem with doing so.

In addition to practical concerns such as carbonation, storage orientation, and intended storage time, corks are also chosen for aesthetic reasons.

Types of cork-finished packages

There are multiple bottle and closure types brewers may choose when corking their beers. Generally corks are used with bottles that have 29 mm openings or larger, but some producers have corked bottles with standard 26 mm openings without problems. If the beverage being packaged is carbonated, you will probably want some sort of closure in addition to the cork to keep the cork in place. The most common choices for this are either caps or wire cages, though some producers use string instead.

Corks do not need to be sanitized [2].

Cork and Cage

 
Colin Burton shows mushrooming a cork with a bench capper after inserting the cork with a floor corker.

Corking and caging can be used for both champagne-type bottles and the brown glass 'fat-lipped' Belgian bottles, both of which are generally thicker glass and rated for higher CO2 pressure. Generally corking and caging is used for bottles with 29 mm openings, though some have cork and cage finished bottles with 26 mm openings. Make sure your bottle type can take corks before using it.

Corking and caging does require some more special equipment. Most wine corkers are designed to push the cork all the way into the bottle, which is not what you want. Brewers will at least want a floor corker for standard wine bottling. These corkers are designed to push the cork entirely into the bottle but they can be modified/adjusted to control the cork depth and leave some cork protruding from the bottle, which is necessary for caging. Bench corkers such as the Colonna capper/corker work as well. Champagne floor corkers are available and make the task of partly rather than fully inserting corks easier, though they are more expensive. It is difficult to control the exact depth of the cork with a two arm corker, and we do not recommend this for corking and caging.

The following gives a step by step process for corking and caging with a non-champagne floor corker. For a more detailed description with pictures, see Dave Janssen's blog post about corking. The more common floor corkers work by both compressing the cork and pushing it into the bottle with the movement of the arm. In order to leave the cork partly exposed, and to control the exposed cork level, place a standard carboy bung on the rod which pushes the cork. This positioning can be adjusted as needed. Push the cork into the bottle until you reach the bung, then bring the arm all the way up. Remove the bung and lower the spring-loaded pedestal holding the bottle. Then, while holding the bottle with one hand, lower the corking arm completely and bring the bottle down, letting the cork be pushed fully out of the compression section of the corker. Play around with cork depth to find the right amount for you for ease of removal based on your corks, bottles and carbonation levels. The amount of cork sticking out should be more than how it appears when it is caged, as the cork is vertically compressed or "mushroomed" during the caging process. See Mushrooming below.

Some corkers may leave a crease or indentation in the cork from the compression mechanism. This is generally not a problem but it if severe enough it may result in leaking of gas or liquid [3]

Raf Soef of Bokkereyder suggests using 26.5 mm cage hoods; champagne cages are too large for beer corks [4].

See also:

Cork Depth

Inserting the cork too far into the bottle can result in a cork that is difficult to remove. It might be necessary to manually "mushroom" the cork in order for the cage to fit. The first image below demonstrates a cork that was inserted about 3-4mm too deep, while the second image demonstrates a cork that was inserted with less depth into the bottle and mushroomed so that the cage will fit [5]:

Example photos provided by Ryan Beal:

  • Cork inserted about 3-4mm too deep. Cork difficult to remove.

  • Proper depth with manual mushrooming to make cage fit. Cork easy to remove.

  • Proper depth before mushrooming and capping.

Mushrooming

"Mushrooming" is the actual or perceived compression of the top part of the cork that protrudes out of the bottle and is often preferred for the aesthetic appearance. Some of the practical benefits of mushrooming are debatable, as is the cause of mushrooming when no effort is made by the brewer to manually compress the top portion of the cork. Some people believe that this compression happens naturally after packaging over time and is due to high carbonation in the bottle pushing the cork out of the bottle, which is held in by the cage. However, in many cases this might be just an illusion of appearance and the cork may not actually be compressed at all, but is either manually mushroomed or just appears to be compressed by the cage due to the much thinner "leg" of the cork which is compressed by the lip of the bottle (see this image for an example). Some people observe that manual mushrooming makes removing the cork easier (due to less cork being inside of the bottle) and allows for more "pop" noise and less CO2 to escape the bottle over time, while others say that mushrooming does not serve any functional purpose and is not necessary as long as the corks used are able to be inserted at a proper depth and the cages fit. Some have noted that in order to insert some corks to a proper depth (see Cork Depth), manual mushrooming must be done so that the cage will fit. See this MTF thread for more opinions from various brewers.

Actual mushrooming of the cork can be accomplished manually by hand, though be aware that flaws in the bottle may cause the neck to break, which would be a very dangerous situation if you are applying the downward force by hand. It can more easily and safely be applied with a bench capper. Put the cage on the cork and compress both with a bench capper. Hold the bench capper arm in place with your shoulder/armpit, leaving both hands free to orient and twist the cage. Special cage twisting tools are available, though pens such as sharpies or some interchangeable screwdrivers are about the right size. You could also use twist lock pliers if you have them around. There are also machines available that will semi-automate this process for commercial brewers.

Adjusting to Wire Twists

The wire cage needs to be tightened under the lip of the head of the bottle in order to secure corks from being pushed out by the beer's carbonation. Typically 4-5 twists are done with wire cages to prevent them from becoming brittle or inconveniently removable. However, with thinner bottle necks, longer wires, or a particular wire twisting tool, more twists may be necessary in order to tighten the wire around the neck under the lip. Modifying the wire cage tightener is a hack to work around this problem. See Andrew Holzhauer's post on MTF for an example of how to modify the wire tightener to account for thinner bottles while still twisting the wire only 4-5 times.

Cork and cap

Corking for cork and cap closures can be used on champagne-style bottles, which are a good source of high-pressure bottles for brewers, but not on 'fat-lipped' Belgian bottles. Cork and cap might let in less oxygen than corking or capping alone. It also protects the beer from coming into contact with a rusting cap or the plastic lining of caps. Under high carbonation, caps can leak if they are accidentally dislodged, but a cork will prevent any significant CO2 from escaping [6].

Corking and capping is much more straightforward than corking and caging as the cork is pushed entirely into the bottle. Generally cork and cap closures are used on bottles with 29 mm openings, though some have done this with 26 mm bottles. Make sure your bottle can handle corks before using them for a cork and cap finish. Although the cork depth is not as important as in corking and caging, the cork still must be far enough into the bottle to not interfere with the cap. Bench corkers are recommended for corking and capping as they allow better control of cork depth than two arm corkers and bench corkers allow the cork to be easily depressed further if it is not far enough into the bottle. For 29 mm bottles, you will also need a 29 mm bell and 29 mm caps for capping.

Large format bottles

To cork large format bottles (1.5 L and up) without specialized equipment for large format corking, you will have to modify a corking process and/or possibly create some new equipment. For 1.5 L (magnum) bottles, standard floor corkers leave slightly too little room between the pedestal and the cork compressing section such that magnum bottles will not fit with the corker unless it is modified. Shortening the spring or finding an alternate shorter spring will provide enough clearance to cork magnum bottles with standard floor corkers[7]. Other methods which MTFers have used include compressing the corks in a corker and then ejecting it and quickly inserting the cork into the bottle by hand [8] as well as hammering the cork in with a machined piece of wood and then mushrooming with a drill press[8]. Hand corkers may also work but with them it is difficult to control cork depth. Vinnie from Russian River reports mushrooming the corks with 2x4 and his body weight[9] (1:22:30 in).

75 cl and 150 cl bottle have the same size opening and 3-9 l bottles have a larger, but consistent, opening. Some MTFers have used normal beer corks in large format bottles while others recommend sourcing larger corks[8].

Videos

Mitch Ermatinger's guided tour of the manual bottling line at Speciation Artisan Ales (questions answered here on MTF):

Levi Funk's guided tour of manual bottling line at Funk Factory Geuzeria:

Using a Portuguese corker:

Using a hand corker (be sure to use beer corks and not champagne corks since champagne corks are too wide; the corks shown in the video below may have been inserted too deeply, especially if better "mushrooming" is desired) [10]:

Equipment

See Also

References

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