text: Compared to most apples, pears tend to have more sugar and total phenolic compounds. The main sugars in perry pears are glucose (192 –284 mg/L), xylose (140–176 mg/g), and galacturonic acid (108–118 mg/g). Types of sugar that are present in the juice play an important role in yeast activity and determine the success of fermentation. Unlike the juice of apples, pear juice contains significant quantities of unfermentable sugar alcohols, particularly sorbitol. The presence of sorbitol can give perry a residual sweetness, in addition to a mild laxative effect.
  Pear juices contain rather low levels of amino acids, sources of nitrogen such as aspargine, aspartic acid and glutamic acid.
  After initial fermentation, many perries go through malolactic fermentation. On average, compared to apples, pears have higher levels of titrable acidity, most of it being citric acid. In environments with high levels of malic acid, such as grape must in winemaking, malolactic fermentation bacteria convert malic acid to lactic acid, reducing the perception of acidity and increasing complexity of flavour. However, if high levels of citric acid are present, as in pear pomace, malolactic fermentation bacteria catabolise citric acid to acetic acid and oxaloacetic acid, instead of lactic acid. This results in a floral, citrus-like aroma in the final product, lacking the diacethyl odour typical for most products that have undergone a malolactic fermentation.