How Are Synthetic Corks Made? (Part I)

Examples Of Two Different Synthetic Corks.This is part I of a two part series. Look for part II later this month.
With each passing year synthetic corks are becoming an increasingly popular way to seal wine bottles. They have proven themselves to be a worthy replacement of the natural cork stopper, whose production costs and shortages have continuously driven their prices up and their quality down.
Synthetic corks are made of high-grade polymer plastics. The inside is filled with a thermoplastic that has elastic qualities. This allow the synthetic cork to give but still retain its shape, much like a natural cork. The outer shell is made of a solid plastic that bends easily, much like rubber would.
The whole idea is to have the synthetic cork act as much like a natural wine bottle cork as possible, in terms of how it is goes into the bottle, how it ages the wine, and even how it goes “pop” when removed from the bottle.
There are two ways to make a synthetic cork. The first way may seem obvious to some, which is to mold them with an injection molding process. This is the same production method used to make everything from plastic lawn furniture to little army men.
The significant issue with this method is that it allows the cork to have an outer shell on all sides making the inner foamy plastic completely encapsulated.
The second way to produce them is by extrusion. This is how everything form vinyl hose to rubber wiper blades are made. The synthetic cork is continually molded as a never-ending long piece. As it is pushed or extruded from the mold it is cut into the appropriate length.
This production method allows the synthetic corks to have a harder plastic outer shell, but only on the sides, not the top and bottom as the injection molded ones due. This means that the foam is exposed to the wine.
Watch for part II of this post, where we will go over the significance of these two production methods.
Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.