It's only safe if you can test the acidity. It must be at least 5% acidity.
I did find this link on how to determine the acidity of vinegar, but I've never done it: http://www.ehow.com/how_8178106_measure-acidity-homemade-vinegar.html
I also found this:

What Does It Mean to You?

This degree of accuracy is generally not something you would do as a home hobbyist making vinegar in the kitchen. If you have made vinegar using wine or fruit scraps, consider it a delightful addition to salad dressings or recipes.
Of course, people have been using vinegar for preservation for centuries without such testing. If you choose to use homemade vinegar for pickling projects, you should at least measure the pH value, and ensure that it is no higher than 4.0. This pH will protect against most harmful bacteria, and against the formation of mold.
For safety, however, if you need vinegar of a certain strength for pickling, we advise that you are best off using a commercial vinegar that has been tested and certified to have a certain strength.

 

Thank you! I'll see if I can test what's in storage, but for now I'll buy some.

 

Couldn't one use something like litmus papers?

https://www.amazon.com/Litmus-Strip...trips-Universal-Application-Packs/dp/B00S730YWG?ie=UTF8&ref_=zg_bs_3013605011_2

 

Couldn't one use something like litmus papers?

https://www.amazon.com/Litmus-Strip...trips-Universal-Application-Packs/dp/B00S730YWG?ie=UTF8&ref_=zg_bs_3013605011_2

You could but the accuracy would be more questionable. Litmus is so easily affected by the environment that it isn't considered very stable. Plus the readings it gives are broad spectrum and open to different interpretations.

The other issue I have with using homemade vinegar is one of appearance. It is often cloudy and the sediment is not appealing to the eye in the finished jars. You can filter it over and over and still not get all the sediment out.