TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Arrangement: The esterification zone comprises either a mixing tank in which it is possible to mix the crude fatty acid fraction with alcohol, and/or distillation unit in which the crude fatty acid fraction is brought to react with alcohol. The arrangement additionally comprises an esterification zone for crude tall oil, in which zone it is possible to bring the crude tall oil to react with formic acid and to give the alcoholic compounds a protective esterification. The arrangement comprises an unit for separating alcohol and water, into which it is possible to direct the overhead product produced in the pre-distillation unit to separate the water and the alcohol. The alcohol source is a storage tank for holding methanol or and/or a tank for recovering methanol.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: When the esterification is carried out by using formic acid, the amount of the free fatty acids which are brought to the esterification of the fatty acids stage is maximized. In the esterification of the fatty acids, at least 80 molar%, most suitably at least 90 molar % of the fatty acids that are contained in the crude tall oil, which is fed into the crude tall oil refinery, are brought to react with a lower alcohol. The esterification performed with formic acid is carried out at 40-145 degrees C by using reaction time of 0.1-30 days, and a molar ratio of 1:1-4:1 between the formic acid and the alcohol groups. The esterification performed with formic acid is carried out at 50-80 degrees C and by using a reaction time of 1-30 days, where the molar ratio is 1:1-2:1 between the formic acid and the alcohol groups. The crude tall oil is treated at an early stage of the process with formic acid, which prevents the esterification of the fatty acids with the alcohols and the sterols which are contained in the tall oil, in the later stages of the process, during storage, during drying and during the separation of pitch. The fatty acids in the composition, which is generated after the separation of the pitch and the resin, are esterified by using methanol, either in the primary oil column of the refinery or in the intermediate reservoir prior to the primary oil column and/or in the reactor vessel in the intermediate reservoir and the primary oil column. The primary oil column, the water generated and the excess alcohol are removed by distillation, in which case at least part of the alcohol is reused for esterification of the fatty acids. The esters of the lower alcohols of the fatty acids are recovered as a tapping from the fatty acid column of a conventional tall oil refinery. During the drying stage of the tall oil distillation, the excess formic acid is recovered along with the water. The reagents contained in the compounds which contain alcoholic hydroxyl groups, and, correspondingly, the reagents required for the esterification of the fatty acids, i.e. formic acid and methanol, are brought into the process as methyl formate. The methyl formate is hydrolyzed, after which the methanol and the formic acid are distilled apart in water, and both of them are separately used for esterification. At least part of the excess formic acid is esterified with methanol, in which case the formic acid, as an ester, is first concentrated by distillation, after which it is returned into the process. Preferred Components: At least 90 (preferably at least 95) wt.%, of the crude tall oil compounds, which comprise alcoholic hydroxyl groups, are esterified by using formic acid. EXAMPLE - No suitable example given.