Practical Preparation Techniques For Wine Bottling

Before bottling, it is imperative to procure packaging materials, bottles, corks or screwcaps, foils (if used), and labels. There are many important considerations. Firstly, what style of bottle will you choose? There are two traditional shapes, the steep-shouldered straight-sided Bordeaux style, or the slope-shouldered shallow-curved Burgundy shape, but the tall and slender “Hock” shape that many German and Austrian wines use is also an option. In general, the Bordeaux style is for Bordeaux style wines (Cabernet Sauvignon, Merlot, Sauvignon Blanc, etc.) and the Burgundian style is for Pinot Noir, Syrah, and Chardonnay. Typically, white and rose wines are bottled in clear glass, known as “flint”. Most red wines are bottles in colored glass, “champagne green” is the darker green shade while “antique green” is the lighter more yellow-green color, but bottles also come in amber, blue, and some colors are available with a “frosted” finish.

In packaging non-vinifera wines such as in the cold-climate regions of the north there are no traditional rules, a Marquette can be bottled in any style of bottle. You can choose whatever style you like, as there are no regulations regarding the shape of a bottle and the wine it contains. However, it is worth considering the traditional shapes because many customers are aware of tradition. Some customers appreciate something different, and breaking-free of traditional norms can make your package stand out from the crowd. 

Another consideration is that Burgundy bottles are wider and shorter, and Bordeaux/Hock bottles are taller and narrower, this may be a consideration for storage of bottled wines on pallets in your specific facility, as it can affect how you pack and stack your pallets.

There is also the “tapered” style of Bordeaux bottle, which is popular and attractive but be aware the taper itself can present numerous challenges to specific bottling and labelling equipment. Applying a label “square” onto a tapered bottle is not always easy to do and can cause many labels to be wasted during testing and adjustment of label application equipment.

It is important to know the specific measurements of the bottle neck and finish, either for a cork or a screwcap finish. There is no one standard measurement for the outside of a bottle neck, and you will need that dimension for choosing a foil that will fit, usually 28.75mm is most popular, but there are alternate sizes, and you need to make sure you are aware of this specification. For standard 750ml wine bottles, the bottle neck typically has an inner diameter of around 18.5mm at the mouth, increasing to 21mm before expanding into the bottle, while a standard wine cork has a diameter of 24mm, often referred to as a #9 cork. 

Be aware that there is a type of bottle finish called a “bar-top”, with a large “ring” around the very end, or mouth, of the bottle. Most standard foils will not fit on this style of bottle. Along with foils some wineries choose to finish their bottles with wax. Though visually distinctive and appealing, wax finishing is labor intensive, and the cost of the hot-dip wax is considerable, and application of wax needs careful consideration.

Whether deciding on a natural cork or an “agglomerated” cork, you should consider that price and quality often go hand in hand. When committing to bottling your wine with a cork, make sure you are purchasing a fresh, quality product from a reputable supplier. A poor-quality cork is responsible for many wines’ early demise. Most cork purveyors will be happy to brand corks with your logo, business name, website, etc. There is usually a nominal art charge for this service and a minimum order amount. Be aware that fresh corks should have a humidity content of 4%. Old or leftover corks may have been allowed to dry out and should not be used, but some suppliers are willing to re-hydrate corks at a nominal fee, or none.

If choosing a screw-cap closure, make sure you are aware of the size and style of the cap and the cap applicator, and whether the bottle you have chosen will fit. This is extremely important; you do not want to be in a position during bottling where you discover your cap doesn’t properly fit your bottle. Rely on the advice and expertise of your packaging purveyors. The original and most-used screw cap is a Stelvin, but not every screw cap bottle uses this style of cap. Ask these questions before you order your bottles and caps, and work with an experienced and reputable supplier.

There are other closures besides corks and screwcaps. Some choose to use a crown cap, the same as a beer bottle cap, especially for any wines with remaining, or potential for, carbonation or additional fermentation in bottle, such as a “pet-nat” style of wine. But again, size is a consideration, most beer bottles use a 26mm crown cap, but be aware that a Champagne-style wine bottle will use a 29mm crown cap. This is another “minor detail” that can make bottling day a disaster. In addition, there is also a type of glass cork with a silicon ring, the Vino-Lok, and there are a great many types of synthetic or plastic corks, all have their costs, advantages, and disadvantages. You should do your research beforehand and remember that some require different or specialized application equipment or may not run well through your equipment.

Be aware there is no legal requirement to use a capsule or other secondary closure. Capsules, also called foils, come in different sizes, and are made from different materials, and each have different costs and minimum order amounts. Many suppliers can print logos or artwork on their foils, and this may be an important consideration for your package’s image on the shelf. Some foils are heat-shrinkable and require that specialized kind of application equipment. Other foils are made of a polylaminate of metal and plastic and must be “spun” or “burnished” onto the bottle top. Again, know your equipment needs and abilities to do these processes before you order your packaging supplies, and make sure you are certain of the bottle’s dimensions before ordering capsules.

Lastly, let’s consider the label or labels. It is permissible to use a wide, single-piece label that contains all the required legal information normally found on a two-piece label, and this can be both a cost and a time savings. But many choose to use the traditional two-piece, front and back, label. You should be aware that wine labels must be pre-approved by the Alcohol and Tobacco Tax and Trade Bureau (TTB) through its online Certificate of Label Approval/Exemption (COLA) system. There is no charge or fee for approval. Do not go to the trouble and expense of having labels designed and printed unless you have received TTB approval for your label content and design. In general, the TTB does not approve labels that include health claims, nudity, or vulgar language on labels. See further information here: (https://www.ttb.gov/regulated-commodities/labeling/colas).

There are many small and large printing companies capable of printing labels. You should inquire if a company has previous experience with wine labels and ask for a list of references and label samples. Costs can vary widely depending on the company, on the number of labels required, and any special label features, like special paper-stocks, custom die-cut shapes, metallic foils, and 4-color artwork, etc. Work with an experienced and reputable company to get everything correct and legal. However, small local companies are sometimes easier to access and to develop a working relationship with, and often they can save some money and are happy to do smaller jobs.

Another consideration is whether to include the vintage year (date) on the label or not, it is not always TTB-required information. There can be substantial cost-savings in printing many years’ worth of labels in advance without including the vintage. Few customers really check or care about a vintage date, and the savings may be considerable. Further information on mandatory label requirements can be found here: https://www.ttb.gov/regulated-commodities/beverage-alcohol/wine/labeling

To start to prepare wine for bottling any use of oak barrels or oak adjuncts must be already completed prior to blending. After the final blend has been made, no further blending or adjustments (except sweetening) should be considered, as any acid or water additions after stabilization may render the wine unstable due to a change in acidity or pH. Now is a good time to have the wine’s alcohol by volume checked for accurate label use, though the TTB does allow a 1-1.5% variance, depending on the wine’s tax-class.

Blending is a true craft, after a winemaker has mastered the basics of making high quality wine, blending is the final tool that can make a good wine into a great wine. Very small additions can provide great changes in the character and quality of a wine. The basic philosophy is to take two or more good wines and put them together to make one great wine. This is not always easy, and sometimes winemakers choose to blend based on a previously made style (or recipe) of wine, or for simple practical reasons such as a greater volume of finished wine is required. Federal law requires that for a varietally-labelled wine, (with the name of the grape on the label), the wine must be a minimum of 75% of that grape varietal. However, blended wines and wines with fanciful names like Opus One are quite popular and acceptable in the marketplace. A winemaker should consider the advantages that can be made by blending wines for color, character, complexity, or simple originality.

Heat stability is only a consideration for white and rose wines. Heat instability, also known as protein instability, can cause a haze to form in the wine after bottling, or sometimes there will be formation of hazy-looking filaments in the bottle. To achieve heat or protein stability, winemakers use bentonite, which is a fine-grained siliceous clay. Bentonite has a negative charge and will attract and bind with positively charged particles, including proteins. The trick is to mix the bentonite properly, adding the bentonite slowly while stirring in enough warm water to dissolve the bentonite completely. The rule of thumb is two gallons of water to one pound of bentonite. This mixture should be allowed to “swell” for at least an hour before the bentonite slurry is added to wine. It is important to mix the bentonite well into the wine with either a tank-mixer, a pump-circulation, or manual stirring for small lots. Each wine will require a different dose of bentonite to achieve heat stability, an in-house bentonite bench-trial can be done, or the wine can be sent to a wine lab for a bench trial and dosage recommendation. Complete information on the use of bentonite in wine can be found here: https://www.extension.purdue.edu/extmedia/fs/fs-53-w.pdf

Cold stability, also known as tartrate stability, refers to the removal of excess tartaric acid in wine that can re-crystallize when chilled. These crystals, primarily potassium bitartrate (KHT or cream of tartar), can form a powdery deposit in the bottle. The traditional method for achieving cold stability involves seeding the wine with powdered KHT and then chilling it to just below freezing. Over 5 to 10 days (depending on the wine and the chilling temperature), excess tartaric acid precipitates out. This process uses a lot of electricity to power chilling equipment.

In the past few years, various other products have been created to prevent tartrates from precipitating by interfering with the point of microcrystal nucleation of tartaric acid. These now commercially available products are either based on potassium polyaspartate (KPA), or cellulose gum. Though these products have been shown to work well, there is one other consideration, the wine’s total acidity. The use of the traditional chilling method can help balance a wine by lowering its total acidity, a definite advantage for wines produced from high acid grapes.

In traditional vinifera red winemaking, cold stabilization is not necessary. However, red wines made from cold-climate hybrid grapes often benefit from cold stabilization via chilling, primarily to help manage and reduce their naturally higher acidity. Further information on cold stability by cold contact can be found here: https://www.extension.iastate.edu/wine/wp-content/uploads/2021/08/coldstabilizationbycontactprocess.pdf

The wine’s final chemistry should now be checked and confirmed, and the wine should also be tested for heat and cold stability, if not previously checked. There are many commercial wine labs across the country, and the money spent having chemical parameters and stability tests done is well worth the price. You can order analyses a la carte or buy a panel of appropriate analyses. The minimum information at bottling is pH, alcohol by volume, residual sugar, free and total sulfur dioxide (SO₂), and volatile acidity (VA). Note: there is a federal limit to the amount of volatile acidity allowed, 1.2 g/L for white wines and 1.4 g/L for red wines. The federal limit for total sulfur dioxide in wine is 350 ppm.

It is vital at this point to measure and make sulfur dioxide additions to maintain a given free sulfur level based on the wine’s style and pH. An MLF-stable dry red wine should have a 0.5% molecular sulfur level at bottling. Non-MLF reds, roses and whites should be maintained at 0.8% molecular. A chart of molecular levels based on pH here: https://srjcstaff.santarosa.edu/~jhenderson/SO2.pdf

If using traditional paper sheet filtration, either plate-and-frame or lenticular style, filtration should commence as close as possible to the day of bottling, the same applies to crossflow filtration. Best practice requires no more than 72 hours between any given filtration step (coarse, polish, or nominal sterile). It is a good idea to do any sweetening prior to the start of filtration, but not so far in advance to risk the start of refermentation. Wine can be sweetened with either sucrose (table sugar), pasteurized grape concentrate, or even unfermented grape juice. Maintaining a proper level of free sulfur throughout this period will help prevent refermentation.

The use of an absolute sterile membrane filter is highly recommended, especially when used with a high-speed monobloc bottling system. There are challenges to ensuring absolute sterility on manual gravity filling and corking/capping systems.  It takes excellent sanitation and hygiene from start to finish to protect against refermentation. This is why many smaller wineries use potassium sorbate as a refermentation inhibitor. Sorbate can help ensure microbiological stability if used in the proper amount. However, be aware that sorbate should not be used on MLF+ wines as there is a risk of developing so-called geranium taint. A complete article on the use of potassium sorbate can be found here: https://www.extension.iastate.edu/wine/wp-content/uploads/2021/09/sorbicacid1.pdf

If you can conduct proper absolute sterile membrane filtration this should be sufficient to ensure bottle stability of sweet wines and all others. Be sure to conduct “bubble point” tests on all membrane filter cartridges both before and after filtering to ensure the integrity of any filter membrane. A description of bubble-point testing can be found here: https://scottlab.com/bubble-point-integrity-testing

There are a few more minor considerations for the bottling period. Make sure you have enough labor for the bottling line, to dump bottles and pack-off after filling, corking, and labelling. You will also need box tape to seal the cases. It’s a good idea to have an ink date stamp to mark the bottling date of each case, this enables accurate tracking of bottled wines over time. Pallets of wine should have a lot-tag or pallet tag to label pallets for bottling date, wine vintage and type, etc., along with marking pens and plastic pallet wrap to keep cases of wine on pallets secure when moving into storage or for shipping.

Many winemakers dread bottling time, as it requires significant preparation, planning, scheduling, and logistics. However, it’s also the final opportunity to end the winemaking process properly and ensure the bottling is done right the first time.