If you like to pickle cucumbers, tomatoes, okra or squash, and you have vinegar on hand, you may want to check to be sure that the vinegar you purchased has 5% acidity.  The University of Georgia Cooperative Extension says that it is extremely important for food safety that the vinegar used for home-pickling is 5% in acidity.

Until recently, cider and distilled vinegar sold in the United States was dependably diluted to 5-percent acetic acid. All U.S. Department of Agriculture home-canning recipes that call for vinegar specify a strength of 5 percent, but shoppers are finding that some vinegar manufacturers are selling 4% acidity vinegar – which cannot be used for home pickling.

The manufacturer’s of the lower-acidity vinegar are not breaking the law – the U.S. Food & Drug Administration requires at least 4% acidity for the product to be sold as vinegar.  The 4% acidity vinegar might be good enough to make some salad dressing, but is not good for long-term preservation.

See this bulletin from the UGA Extension Service below: