Fermentation Cap for Ball Canning Jars

Am looking at different food/cooking alternatives to improve health. As such, one of the local live/raw food places held a class last week about fermenting vegetables, and mentioned that canning jars might be ideal for small batches to try things out, hence this thing was created.. As an example of fermentation, look at a random book on amazon about it (http://www.amazon.com/Wild-Fermentation-Flavor-Nutrition-Live-Culture/dp/1931498237/ref=sr_1_1?ie=UTF8&qid=1288841311&sr=8-1).

When ferment