Bottling and Closures

Before bottling, the wine's dissolved gases are adjusted by sparging, bubbling nitrogen and/or carbon dioxide through it until dissolved oxygen and carbon dioxide reach the desired levels. The wine is then typically filtered in-line on its way to the bottling line. For wines that need microbiological stability, the last filter is an absolute membrane, one with a precisely defined maximum pore size, which removes microorganisms. Every surface the wine touches after filtration, from hoses to the rinser, filler and closure applicator, must be cleaned and sanitised. Heat is another route to stability. The OIV defines pasteurisation as heating wine to a specified temperature for a given time to inhibit microorganisms, and describes it being done by passing wine through a heat exchanger, by bottling the wine hot, or by heating it in the bottle.

• Wines being sterile filtered should be bottled immediately; filtering to a tank and bottling days later allows time for microbial growth

Total package oxygen, or TPO, counts the oxygen dissolved in the wine plus the oxygen in the headspace, the unfilled gap between wine and closure that leaves room for the wine to expand with temperature. High TPO can lead to premature oxidation during bottle ageing, affecting flavour and aroma. According to the AWRI, if bottling TPO is not well controlled, its impact can be more significant than the oxygen that seeps in through the closure over the whole life of the wine. In the first two to four months after bottling, the headspace and the oxygen trapped in the closure itself are the main oxygen sources, and they indirectly strip away free sulfur dioxide, the wine's key antioxidant.

• Fill height, wine temperature, inert gas use and bottle size all influence headspace oxygen
• Headspace oxygen is generally higher under screw caps than under cylindrical closures, because screw cap bottles are filled with more ullage

A typical line runs through these steps in order.

• 1. Adjust gases: sparge the final blend with nitrogen and/or carbon dioxide so dissolved oxygen and carbon dioxide reach their target levels.
• 2. Filter in-line: pass the wine through its final filter on the way to the filler; an absolute membrane is used where sterile filtration is wanted.
• 3. Rinse the bottles: clean inverted empty bottles with filtered water or, more commonly today, filtered air.
• 4. Purge with inert gas: sparge empty bottles on the filler with inert gas and keep an inert gas cover on the filler tank, aiming to keep dissolved oxygen below 0.5 mg/L.
• 5. Fill to height: fill each bottle to a set height, by gravity on small lines or, on large lines, on a rotary carousel of up to 120 filler heads using counterpressure or vacuum.
• 6. Protect the headspace: displace headspace oxygen with vacuum, inert gas or liquid nitrogen droplets.
• 7. Seal: apply the closure; a screw cap needs inert gas dosed into the cap immediately before application, and a cylindrical closure applied without vacuum can add about 1 mg/L of headspace oxygen.
• 8. Check: measure dissolved oxygen in the first bottles at start-up to confirm gas cover, then usually hourly through the run.

The closure goes on last, and oxygen keeps diffusing through it as the wine ages. AWRI trials show that its oxygen transmission rate, the rate at which oxygen passes through it, can significantly affect shelf life. Very low rates can lead to reductive attributes where precursors are present; low rates can help retain fresh fruit; moderate rates can bring cooked and stewed fruit characters; high rates can produce oxidised characters over a relatively short shelf life. For a closure-by-closure look at cork taint, technical corks, screw caps and synthetics, see our Alternative Wine Closures article.

• Natural cork: permeability can vary widely depending on the grade of cork
• Technical (agglomerated) cork: lower variability than natural cork, with low to moderate oxygen transmission
• Screw cap: very low to low oxygen transmission with a high degree of consistency
• Synthetic: typically moderate to high oxygen transmission, with significant variability between products

Primary sources: https://www.awri.com.au/industry_support/winemaking_resources/storage-and-packaging/packaging-operations/oxygen-pick-up-during-packaging-understanding-total-package-oxygen/, https://www.awri.com.au/wp-content/uploads/tpo_fact_sheet.pdf, https://www.awri.com.au/industry_support/winemaking_resources/storage-and-packaging/packaging-operations/steps-in-the-packaging-process/, https://www.awri.com.au/industry_support/winemaking_resources/storage-and-packaging/pre-packaging-preparation/filtration-physical-removal-of-microorganisms/, https://www.awri.com.au/industry_support/winemaking_resources/storage-and-packaging/packaging-operations/bottling-line-sanitation/, https://www.awri.com.au/wp-content/uploads/2019/03/oxygen-transmission-rate.pdf, https://www.oiv.int/standards/international-code-of-oenological-practices/part-ii-oenological-treatments-and-practices/wines/pasteurisation, https://www.oiv.int/standards/international-code-of-oenological-practices/part-ii-oenological-treatments-and-practices/wines/bulk-pasteurisation, https://www.oiv.int/standards/international-code-of-oenological-practices/part-ii-oenological-treatments-and-practices/wines/hot-bottling. Last verified 2026-09-24