Jar Cakes

Elaine,
I had been busy baking jar cakes for about six weeks and was having good results with them.I was even selling quite a few of them. One day though I noticed several of them had become unsealed after about three weeks (all being applesauce or pumpkin)even though I stored them in cool, dark place.They had no visible mold but smelled moldy and had a greyish color.
I contacted my local agricultural extention service to find out what might be causing my jars to become unsealed.The nutrition specialist and microbiologist advised me of the danger of botulism poisoning and said that the jars may be coming unsealed because of gases produced from bacterial action.
I'm hoping someone that has been making these for awhile can give me their opinion on this and that there is a safe way to make these.

Editor's Note:
Please be cautioned that no matter what you may read on the web about storing cakes in jars that the seal does not make them a 'canned' product. Info from the National Food Safety Database:

Canning Breads and Cakes
Angela M. Fraser
Canning breads and cakes is not true canning. It is the process of baking the product in canning jars and capping them as they come out of the oven. Usually, a weak seal will form as the product cools. This is not a shelf-stable product and so must be stored in the refrigerator or freezer to prevent microbial growth.

Title: Jar Cakes
Posted By: Rochelle, CA
Date: July 7th 2001
Board: recipelink.com Canning and Preserving

It is not recommended that jar cakes be kept longer than a couple of weeks and even then they should be refrigerated or frozen. The temperature in the batter doesn't get high enough and it doesn't penetrate the batter sufficiently to prevent bacteria from growing.