TECHNOLOGY FOCUS - BIOLOGY - Preferred Enzymes: Esterases from, e.g. Thermomyces lanugenosus, Candida antarctica A or B, Aspergillus niger, Pseudomonas fluorescens, Penicillium camemberti etc. (15 species listed), or from porcine pancreas. Preferred enzymes are lipases, especially 1,3-specific lipases, more especially lipase from Thermomyces lanugenosus.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Compositions: Compositions (I) with an acid number of not more than 5, containing at least 10 wt.% monoglyceride and/or not more than 5 wt.% triglyceride, preferably containing 30-70 wt.% methyl and/or ethyl esters, 10-30 wt.% monoglyceride and 1-30 wt.% diglyceride (i.e. esters of 8-22C fatty acids (saturated or unsaturated, linear or branched)). Preferred Method: The esterase is deactivated in a further stage. Alcoholysis is carried out at 10-40degrees C with a water content of 0.1-10 wt.% based on triglyceride. The amount of esterase used is 0.05-2% of the commercially-available liquid preparation based on the amount of triglyceride. Esterase-activating salts comprise hydroxides, carbonates and phosphates of sodium, potassium, calcium, magnesium or ammonium, dissolved in water and used in amounts of 0.00001-1 wt.% based on triglyceride. The triglycerides are derived from fats and oils with a high content of mono- and/or poly-unsaturated fatty acid, especially sunflower oil, rapeseed oil, thistle oil, soya oil, linseed oil, peanut oil, tallow, olive oil, castor oil, palm oil and used oil, e.g. used frying oil; the preferred alcohol co-reactant is ethanol, used in amounts of 10-50 wt.% based on triglyceride. Alcohol and/or water is partly or completely removed. EXAMPLE - A mixture of 1200 g rapeseed oil, 75 g ethanol, 0.375% water (based on oil content) and 0.025% 1-M sodium hydroxide solution was cooled to 15degrees C, treated with 0.25% Lipolase (RTM: lipase from Thermomyces lanugenosus), incubated for 48 hours at 15degrees C with the addition of a further 75 g ethanol after 2.5 hours and 150 g ethanol after 5 hours, and then heated for 1 hour at 80degrees C to deactivate the enzyme. GS analysis of the single-phase product showed 58.2% ethyl ester, 25.6% monoglyceride, 17.1% diglyceride and 0.7% triglyceride (% peak areas, not including free ethanol which amounted to 12 wt.% of the product). Any free glycerol in this and similar products could be removed by washing with water. A mixture of ethyl ester, monoglyceride and ethanol (with less than 0.05 wt.% glycerol) was tested as a biofuel additive in standard diesel fuel; the modified fuel showed CFPP test values of -15, -15 and -14degrees C for biofuel concentrations of 2.5, 3 and 5% respectively.