TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The reticulated hydrophilic solid is neutral selected from silica gel and/or zeolite and is granular or in form of beads. The silica gel or zeolite comprises non-acidic chemically reactive groups. The zeolite is modified by an alkylsilane and is impregnated by non-acidic organic or inorganic molecules. The mixture comprises reticulate hydrophilic solid 0.1 (preferably 1) wt.%. The liquid acid catalyst is sulfuric acid, hydrochloric acid and/or phosphoric acid. The oil or fat is soap stock, beef tallow, coconut oil, corn oil, cottonseed oil, lard, olive oil, palm oil, palm kernel oil, peanut oil, soybean oil, linseed oil, tung oil, sunflower oil, safflower oil, canola oil, rapeseed oil, sesame oil, babassu oil, perilla oil, oiticica oil, fish oils, menhaden oil, castor oil, Chinese tallow tree oil, Physic nut oil, Cuphea seed oil, microalgal oils, bacterial oils, fungal oils and/or grease trap residues. Preferred Reactor: The reactants are conveyed from the inlet to the outlet through reticulated hydrophilic solid. The chamber is an elongated chamber (preferably tube) having first and second end and where the inlet is located at the first end and the outlet is located at second end. The device for conveying the mixture is a pump. The reactor further comprises means for maintaining the reticulated hydrophilic solid inside the chamber while allowing passage of the reactants through the outlet and is operated in continuous mode or in batch mode. Preferred Process: The process is carried out between room temperature and boiling point of alcohol. The oil or fat, alcohol, and liquid acid catalyst are mixed together prior to being introduced in the chamber.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The oil or fat comprises free fatty acids 25 (preferably 15 or 40) wt.% or triglycerides that have been hydrolysed prior to oil or fat introduced in the chamber. The ratio of alcohol to free fatty acids in the mixture is 3:1 to 50:1. The alcohol is methanol, ethanol, propanol and/or butanol (preferably methanol). EXAMPLE - Esterification of hydrolyzed triglycerides after saponification for production of biodiesel was carried out as follows: Saponification of pure canola oil (500 g) was carried out for 150 min at 100degreesC with NaOH (147 g) under constant agitation to melt all solids and transferred to separatory funnel for decantation. After 30 min at room temperature, the lower aqueous phase was discarded and top oily phase was dried overnight to form oily phase (free fatty acids) (acid value was 171.7 mg KOH/g). The free fatty acids was esterified at 31degreesC with methanol in presence of H2SO4 and silica gel. After 12 hours, the quantity of free fatty acids was reduced to 41% of original quantity. More methanol was then added to make the molar ratio of methanol to free fatty acid of 11.6:1. After 25 hours, the residual free fatty acid content was less than 6.7% of initial value. The silica gel was allowed to sediment and two upper phases (oil and methanol) were recovered. After workup, an oily phase (biodiesel) was collected and dried for 120 min. The yield of biodiesel obtained was 89% with respect to the weight of original free fatty acids. The acid value of the finished biodiesel was 3.99 mg KOH/g.