What is "mother of vinegar"

Vinegar \Vin"e*gar\, n. [OE. vinegre, F. vinaigre; vin wine (L. vinum) + aigre sour. See Wine, and Eager, a.]

1. A sour liquid used as a condiment, or as a preservative, and obtained by the spontaneous (acetous) fermentation, or by the artificial oxidation, of wine, cider, beer, or the like.

   Note: The characteristic sourness of vinegar is due to acetic acid, of which it contains from three to five per cent. Wine vinegar contains also tartaric acid, citric acid, etc.

2. Hence, anything sour; -- used also metaphorically.

   Here's the challenge: . . . I warrant there's vinegar and pepper in't.
   --Shak.

   Aromatic vinegar, strong acetic acid highly flavored with aromatic substances.

   Mother of vinegar. See 4th Mother.

   Radical vinegar, acetic acid.

   Thieves' vinegar. See under Thief.

   Vinegar eel (Zo["o]l.), a minute nematode worm ( Leptodera oxophila, or Anguillula acetiglutinis), commonly found in great numbers in vinegar, sour paste, and other fermenting vegetable substances; -- called also vinegar worm.

   Vinegar lamp (Chem.), a fanciful name of an apparatus designed to oxidize alcohol to acetic acid by means of platinum.

   Vinegar plant. See 4th Mother.

   Vinegar tree (Bot.), the stag-horn sumac ( Rhus typhina), whose acid berries have been used to intensify the sourness of vinegar.

   Wood vinegar. See under Wood.

Mother of vinegar is a substance composed of a form of cellulose and acetic acid bacteria that develops on fermenting alcoholic liquids, which turns alcohol into acetic acid with the help of oxygen from the air. It is added to wine, cider, or other alcoholic liquids to produce vinegar. Mother of vinegar is also known as Mycoderma aceti, a New Latin expression, from the Greek μὑκης (fungus) plus δἐρμα (skin), and the Latin aceti (of the acid). The naming of the bacteria has been rather fluid due to its original identification near the inception of bacteriology. Currently, the preferred naming is Acetobacter aceti.

Mother of vinegar can also form in store-bought vinegar if there is some non-fermented sugar and/or alcohol contained in the vinegar. This is more common in unpasteurized vinegar. While not appetizing in appearance, mother of vinegar is completely harmless and the surrounding vinegar does not have to be discarded because of it. It can be filtered out using a coffee filter, used to start a bottle of vinegar, or simply ignored.