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Glass Wine Bottles Still Favored by Consumers
Aug 19, 2016

New wine packaging methods have become more common in the past several years, but the fact remains that most wine is sold in standard 750 ml bottles.  Glass wine bottles are still the most popular choice for winemakers, for both their ability to preserve the aromas and tastes of wines and by contributing to the consumer’s perception of a quality product inside the bottle.”

All glass factories run 24 hours a day, seven days a week. Glass is created from raw materials, such as limestone, soda ash, sand, and cullet, which is recycled glass from both within the plant and post-consumer glass.

Recycled glass saves both on raw materials and energy.  Some glass factories now use up to 70% recycled materials. Since glass is 100% recyclable, there is little likelihood that plastic will be a viable replacement anytime soon.

Back to the manufacturing process. Once materials are weighed and mixed, they enter the furnace, where glass temperatures can reach between 2,100-2,800 degrees. Inside the furnace, the glass must be kept on a very consistent level, which means a tolerance within 1/100th of an inch.  This keeps the glass homogeneous, the key to a quality glass bottle.

Next, the melted glass, which looks like bright orange lava, goes into a forehearth and then a forming machine to create the shape of the wine bottle. Each wine bottle has its own specific mold (think of it as a mold you use for cooking cookie shapes) and if the bottle size or shape changes, the entire line has to be shut down to change out the molds.

During the bottle manufacturing process, temperatures reach 2,800 F.

Once the formed glass bottles leave the mold at temperatures around 850 degrees, they move down the line to receive a special hot end coating. The bottles next go into the annealing lehr, a very large kiln, to reheat the glass to 1,150 degrees and then the bottles gradually cool. This process reduces stress on the containers and naturally strengthens the glass.

Next, the bottles go to a cold end coater, which adds a coating so they do not scrape each other. If scraping occurs, the bottles become slightly roughened.  This could make the bottles “walk up” on each other during the filling line process, which gums up the works.

Finally, the bottles enter a final fast cooling section to bring the temperature down to 100 degrees.

Following manufacturing, glass bottles go through a series of tests. (Think of it as the Crossfit for bottles.) The bottles are first put through a pressure roller to test for breakage. The thickness of the glass is measured and the opening of the bottle is checked to be level and of an exact diameter.

A series of cameras inspect for minor visual irregularities, which can include iridescent, scratches and blemishes. If the imperfections were allowed through the line, the scratched bottles are more likely to break during filling or distribution. 

Each bottle is also stamped or printed on the bottom with a series of numbers or letters. If any bottle is returned due to irregularities, the factory will know exactly which line it ran on and what batch it was from.

Since so much emphasis is spent on looking at packaging in the wine industry, wine bottles must have a lower level of imperfections than other glass in the beverage industry.

After the inspection process, each bottle is sent on rollers or conveyor belts to be packaged in cartons, cases and pallets. The entire process can take anywhere from 36 to 48 hours, depending on the furnace pull.

If there are different colors added to the furnace it can take 5 to 14 days to make the gradual change, depending on the color, while keeping the furnace level within 1/100 of an inch.”

For example, if the furnace is running green claret bottles and a change must be made to run clear flint bottles, the glass plant is required to slowly dump all colored glass raw materials out of the furnace. This gradual change over 5-14 days is necessary to keep the glass homogeneous enough to produce high quality bottles.

Plus, if the bottle size changes, the entire line can be down four hours to make the switch molds and another four hours to get back above 60% productivity.

Due to this long complex process, its essential that all wineries, small or large, get their bottle orders in as soon as they can. It takes so long to switch between colors and the need to change molds to run different bottle styles, therefore glass factories will often have a production plan mapped out months ahead of time.

Wine bottles have been part of the wine drinking experience since Roman times. It’s very likely that wine served in bottles will be the norm for future generations also.