Does Parafilm Really Prevent Evaporation? The Science of Storing Old Bottle Whisky Through Numerical Data
Among whisky enthusiasts, using Parafilm to prevent the "liquid level drop (evaporation)" associated with the long-term storage of unopened bottles has become an iconic practice. However, there has been much debate regarding its actual effectiveness.
In this article, we will examine the material properties and permeability of Parafilm based on objective data and consider its true efficacy in whisky storage.
1. The True Nature of Parafilm
First, what we commonly call "Parafilm" as a general noun is actually a registered trademark of the Bemis Company and a specific brand name. Much like "Stapler" or "Scotch Tape," the product name has become a common noun due to its overwhelming convenience.
While similar sealing films exist, Parafilm remains the top choice both in Japan and internationally due to its ease of use and global recognition. The material is a blend of polyolefin and paraffin wax, and the name itself is derived from paraffin wax.
2. Physical Performance of Parafilm in Numbers
Let us look at the specific specifications of Parafilm in detail.
- Elasticity: Stretchable up to 200% at 21°C. It can partially return to its original size between 82°C and 93°C.
- Operating Temperature: Usable from -45°C to 50°C.
- Oxygen Permeability: 150 cc/m²/24 hours (at 22.8°C, 50% relative humidity)
- Carbon Dioxide Permeability: 400 cc/m²/24 hours (at 22.8°C, 50% relative humidity)
- Water Vapor Transmission Rate: 88 g/m²/24 hours (at 37.8°C, 90% relative humidity)
3. Application to Whisky Bottles: Permeation Simulation
How much permeation do these specifications actually allow through a whisky bottle neck? We will calculate this assuming the surface area of a typical bottle neck (assuming a radius of 2 cm and a height of 3 cm) is approximately 0.0012 m².
■ Oxygen Permeation Amount
Based on the calculation formula, the daily oxygen permeation is approximately 0.18 cc.
This is equivalent to only 0.036 of a teaspoon. In reality, considering the oxygen ratio in the atmosphere (approx. 21%) and the barrier effect provided by a high-quality cork, the amount of oxygen that penetrates is practically infinitesimal.
■ Water Vapor Permeation (Accumulated over One Year)
Similarly, calculating the water vapor permeation on an annual basis yields the following results:
- Annual Oxygen Permeation: Approximately 65.7 cc (approx. 4.38 teaspoons)
- Annual Water Vapor Permeation: Approximately 0.38544 g
4. Conclusion: Is Parafilm Truly Effective?
The conclusion drawn from this technical verification is that the use of Parafilm is a highly effective method for the long-term storage of whisky.
However, to maximize its effect, the following points must be observed:
- Use Sufficient Length: To achieve a practical barrier effect, it is recommended to wrap at least 20 cm of film tightly around each bottle.
- Storage Environment Temperature Control: Since the heat resistance limit is 50°C, the film may deform and lose its function if left in high summer temperatures, sealed warehouses, or car trunks.
- Annual Maintenance: Considering degradation over time, replacing the film with a new one every year is key to preserving the value of your collection indefinitely. Note that old Parafilm can stick to the bottle or cause discoloration of the cap seal.
Postscript
The observations above are simulations based on technical specifications. Although I have only recently begun learning about the profound world of whisky, I have organized this objective data to empathize with the feelings of enthusiasts who cherish every single bottle. One thing to note is that if Parafilm is left attached for a very long period, it may become difficult to remove cleanly due to aging, or in rare cases, lead to discoloration or damage of the cap seal.
To avoid these risks and preserve the aesthetic of the bottle, it is very effective to first wrap the bottle neck with a protective layer of commercial plastic wrap (as shown in the image) before applying the Parafilm for a hermetic seal. We hope you find this useful as a way to maintain your precious collection in peak condition.