Performance determination of Acetobacter

① Microscopic examination: Cells appear as neat ellipses or short rod-shaped shapes.
② Qualitative analysis of acetic acid: Take 5mL of fermentation broth in a clean test tube, neutralize it with 10% NaOH solution, add 2-3 drops of 1% ferric chloride solution, shake well, and heat to boiling. If a reddish brown precipitate is produced and the original fermentation broth has become five colored, it can prove that it is acetic acid.
③ Determination of acidity: Take 1mL of fermentation broth into a 250mL triangular flask, add 20mL of neutral distilled water and 2 drops of phenolphthalein indicator, titrate with 0.1mol sodium hydroxide solution until slightly red, and calculate the acidity.