STUDIES ON METfiODS OF PA~HOILJ ~G . ·~. •, ,~' "< ·- -PRESSURE PA ~BOILIN G. , '' i N.G;C. lENGAR, R: BHASKAR, P. DHARMARA JAN,*,• ABSTRACT .. ··;·, ,f~ . " ' 't~ A meth od of quick parboiling pf paddy has .been worked out using high pre- · ., ,ssure steam wh ich reduces the soaktng and parboiling to 1.5 hrs per batch. The process is cheap in comparison with the methods of parboilmg being carried out _;;. in this country. The method is very suita]Jle for small units located in rural areas, .. -'particularly when combined wi th boilers fired by paddy hu3k, for producing steam and power for parboiling·and drying. ·By this method, breakage of the kernels is ,,, reduced considerably. The mill eut·turn capacity of this method of parboiling is very high and ·a product with a high consumer appeal can be turned out. · Introduction ' ~ .,. ' ·.... At present a large prorortion of rice consumed in India is p1rboiled. Various methods of parboiling are used. In the household method the washed paddy is placed in an open vessel and covered with cold water to a level of 50 mm above the surface of the paddy and heated gently to simmering temperatures just below boiling point of water. This " temperature is maintained overnight. After this, the water is drained off and paddy is steamed until steam emerges at the top. Steaming is done for 5 minutes. The steamed paddy is dried under sun. The product is uniformally soaked and- well parboiled without any off odour, and has an attractive colour. In the commercially adopted, "traditional method", as followed in South !nd!a,_open_air soaking tanks pf larga capacity are used. Cold water soaking upt62ili~.~ is f~fo~ed ' with or without d~il y change of soak w:ater. At the end of the soaking period water is drained off and the wet soaked paddy steamed in open steaming ke ttle for 15 minutes using low pre~su.r_e _steam. ..~,u, , drying in open, is followed h; l~ t~~~J ll].~t ho:d! thQ_Mg~ - g~od SOaKi?k' iS achie~ee an~ > a l!ght COJ_our~~ -!ice is got, therets m~arJabl y ~., ~ont~m!~tf8p by soil at);~tf~~cal _ bac_fiBha, whi_ch ~re mtro~~?ed by uncleaned paddy, lllnTrea~d w~ter ana by du~t ; c?~ta .~~,pr;~,tJOn IU Qpen ,ttl~' Jtiuks: · 'Jlne ~' result is an active fermen\'!lg{'6I1ff)V.hiah f.e'S'tffts in the 'production of protein breakdown products which are absorbed by the paddy and impart a foul odour to it. During open drying the burst kernel acquires fu ngal infection. During drying, tne paddy is freely attacked by crows and sparrows. To reduce the soaking time, double steaming is done, the initial steaming being done on the raw dry paddy for 15 minutes. This to a certain extent sterilizes the paddy and the microbial load is reduced. This position is further improved by daily change of water. The result is an improved product. Soaking time is reduced to 48 hqurs *Resea1ch and Development Laboratory, Tanjore Gooperative Marketing Federation Ltd., Tiruvarur (Tamil Nadu). 40 J. Agril. Engg, '.. ' I ' by this procedure. In order to improve the hygiene of the method of parboiling to reduce the soaking tr me and to eliminate the smell, the method evolved by CFTRI Mysore, using hot soaking for 3.5 - 4 hours at 70 - 75°C was recently introduced Steaming is done in open kettles and drying is done on open plinths. Introduction of mechanical dryers was the next im provement in the parboiling procedure The latest improvement has been a chemical method for preventing the opening of the soaked paddy and for reduc­ ing the drying time of parboiled paddy. This method evolved by Dr. V. Subrahmanyan and Mr. B.S. Vasan at TCMF Lab uses brine containg 15% Sodium Chloride as an osmotic agent. When the hot soaked paddy is treated with brine of this concentration, the salt which is retained at the bran layer, exerts an osmotic action which helps in the quick removal of water from the kernel of the soaked paddy. The salt does not permit any water to move in the reverse direction. If such paddy is then steamed, parboiling occurs at 23 - 24% level of moisture on the kernel. At the end of the parboiling operation the kernel has a lower moisture level than the hw.k and the sodium ion acts as a pump which facilitates transfer of moisture from the kernel to the husk. Thus drying effort, the drying time and cost are greatly reduced. The drying time, using LSU driers is reduced from 4- 5 hrs to 1.5 hrs. Any method of mechanical or chemical chemical drying under humid condi­ tions is an asset in South India where during the N. E. Monsoon. the sky . is overcast for weeks and drying of parboiled paddy is impossible. At present the result is that parboiling operations have to stop du.ring this period. However the present methods of parboiling whether in H uller, sheller cum polisher, or rpodern rice miHs suffer from the fact the methods are ong and complicated. The authors felt that if the soaking period is reduced or even elimina .ed and the process made more simple and hygienic and if the soaking and parboilmg are combined in a single operation, it would be a great advantage. With this object in view, the present work was taken up. Methods and Mate ials After a series of laboratory trials covering a number of pad Jy vanettes the authors an ived at the following procedure as a first measure : (a) waslmg and cleaning of paddy to remove the chaft and immature grains which cause discolouration in final material and reduce the yield (b) raising the temperature of soaked water to 95°C and maintaining it at that ternpature for 20 minutes. This avoided the white bel y formation considerably. Soaking was s~tisfacto ry. (c) Draining off the water and letting i'l the open steam and rarsing the pressure of the vessel to 10 psi (d) maintaining at 10 psi fo r 20 minutes (e) At the end of this period the paddy was unloaded and dried. The resultant product was a tough grain with a light yellowish colour which could be easily shelled even at 17% moisture content and the breakage during milling was negligible (0.5 to 2%) If dried immediately after unloading from the parboiling plant, the•entrapped heat (which was considerable) permitted quick drying. Even shade drying under a fan was rapid. The drying time on LSU driers was at least 1.5 hrs Jess than on the paddy parboiled by CFTRI 'llethod. 2) As a seco r.d sta~e. an attempt was made to avoid soaking altogether. (a) The Vol. IX, Nu. 4 41 paddy W<!S given a wash to remove sand, chaff and immature grains The wash water was drained off (This water can be used repeatedly at least thnce for washing) (b) The washed paddy was loaded into the autocla:ve and open steamed for 20 - 30 minutes c) At the end of the steaming period the exhaust valve was closed and the paddy subjected to pressure treatment for 20 minutes at 15 psi. The resultant product was uniformly parboiled, without any white bellies and had a tough resistant texture which allowed of better shelling and reduced the percentage of brokens oonsiderably. The White belly percentage W.ls negltgible and. the colour was a light golden yellow with a very light brownish off tint. This off tint could be reduced by quick cooling and drying under a free flow of air at rooom temperature. 3) As the possibility of the pressure over a period causing browning was pointed out an attempt was mad<! to reduce the period of pressure treatment and the pressure itself. Lower pressure (5 psi and 10 p ~ i) even at 20 minutes level yield whi e bellies and increased breakage. The colour build up gradully. Treatment at 20 psi for a short period of 5 minutes however achieved the objective. The colour of the product was light breakage minimum and no white bel lies were present. By this procedure, the entire parboiling proce­ dure starting from dry paddy could be completed within 1 hour allowing for ample time for the processing details. 4) Though a very latge number of paddy vanettes were tried out successfully, the major part of the large scale trial work was done on varieties common to Tanjore District namely Co-25, ADT-27 IR-8, ASD-11 & ADT-8. For these varieties the ideal treatment recommended is 20 minutes soaking at 100°C draining off water and 10 minutes of auto­ claving at 15 psi. Large Seide Trials Large industrial scale trials to test the efficacy of the method were carried out by using batch extractor installed at the Bran Oil Solvent Extraction pic nt located at T.C.M.F. Two lots of ten tonnes each were processed in 15 tonne batch extractors and a large number of trials were carried out in 1.5 tonne baby extractors of experimental type. Nearly 370 tonnes of paddy were parboiled by this method. Soaking was uniform and the strength of the grain was very good, with the result that the shelling and milling efficiency were quite high. The product was of a high second class quality with a high consumer acceptability. One of the significant finding was the uniform, high extractable oil content of bran. The rice had a glistenfng appearance with a uniform light colour.