Rubber o-rings, sanitary gaskets, and tri-clamp gaskets are used across the food, beverage and medical industries. When using an o-ring in a beverage application, certain ingredients in rubber formulations can bleed out and change the fluid it is intended to seal. This means that certain rubber seals can actually change the taste of craft beer during the brewing process.
When they discovered this, the engineers at Apple Rubber set out to find the best seals for craft brewing. They needed to determine:
- Which rubber compounds result in the lowest volume swell and create the most effective seals
- Which ingredients in seal materials change the taste of beer
The Process
Our engineers began by preparing and testing five common FDA compliant materials. The materials selected were:
- Nitrile (32BN7AP)
- EPDM (53EP7AP)
- Fluorocarbon (27VT7AP)
- HCR Silicone (13SL7SX)
- LSR (14SL7ML)
For our craft beer selection, our engineers wanted to work with a variety of styles in order to get a broader understanding of how the differences between these beers could affect the elastomers.
Representing common light and dark styles were:
- Ellicottville Brewing Company’s Ellicottville IPA
- Southern Tier’s Double Milk Stout
- Great Lakes’ Dortmunder Gold Lager
MackJac Hard Cider Black Currant Passion and Westbrook Brewing Co. Gose were also tested because ciders and sours tend to have a higher acidity, an important factor to consider when looking into seal materials.
Testing Seal Compatibility
To test seal compatibility with the different brews, we submerged test pieces at 37°F and 194°F for 168 hours and measured the volume swell of the materials. Volume swell is used as a general indicator of how resistant a material is to a given fluid. Another potential outcome is a negative swell. In this case, the fluid actually extracts something out of the rubber, which is undesirable because:
- The extracted chemicals end up in the beer, potentially altering the taste
- Due to that same extraction, the seal shrinks in size and begins to leak
Taste Testing
Thirty mason jars were numbered and used to test each material in all five beverages and in tap water, which would act as a control. After 168 Hours at 37°F, the test specimens were removed from their jars.
The nitrile and EPDM were so strong that their presence in the beer could be smelled before anyone even tasted them. As an extra test, we wanted to see if we could eliminate this change to the beer.
Since we determined that post-cured materials performed best, we wanted to see if adding post-cure to the EPDM and nitrile could burn off any chemical that might be altering the taste of the beer. The results were very promising, and there was no longer any smell and almost no detectable change left in the taste of the tap water.
The Key Takeaways
Looking at the overall volume swell data, the silicone materials were virtually unaffected by any of the brews. In our opinion, the only materials that performed poorly were the 32BN7AP material in high acidity sour beer and the 27VT7AP, which had a negative swell in the stout. The post-cured materials also performed best when it came to the taste testing in the various brews and water. If you want a quality seal that won’t affect the flavor of your beer, silicone is the best choice for your craft.
Enjoying Solved and Sealed?
Check out our full report on craft brewing seals and some of our other case files here!