DEVELOPMENT/RESEARCH NOTES 4

RECENT DEVELOPMENTS IN THE PRESSURE OF PADDY -DIRECT PAH.

N.G.C. IENGAR, N.S. GANGA.DHARAN AND G. RAJENDRAN*

During a study of the various methods of with double -which steps up the steam parboiling, the authors observed that soaking of consumption and its cost - the time taken is not paddy -whether in cold water or hot water - was less than 20 - 23 hours. a factor which either increased the cost of opera­ tion - if done by the hot soaking method - or b) Hot Soaking prolonged the operation gn:atly and brought in some leachate loss with attendant foul smell and i) The production of hot water is costly. A taste - if done by in cold water for good deal of steam wh!ch should be used for three days. The authors felt that if this part of better purposes like running the mill is being the parboiling operation could be reduced or used for producing hot water. Though a sugges­ eliminated altogether it would be a significant tion has been made that this hot water could be saving in cost and effort. ptoduced dire..:tly by heating water on a hu ~ k­ fired furnace thereby reducing wastage of steam. The disadvantages of so~king are : This has not yet been adopted. The use of steam for producing hot water is a double waste of a) Cold Soaking steam. This increases the cos t.

i) Leachate loss due to the breakdown and ii) The soaking operation requi1es at least diiso\ution of starch and carbohydrates as a three to f<>Ur hours and involves the use of very result of the metabolic or autolytic activity of the costly and elaborate equipment. paddy due to the high level of moisture content which is usually attained during the cold soaking lhe authors felt that if a method can be and which will activate the enzymes in paddy. found for parboiling which shortens the soaking operation or eliminates it altogether, considerable ii) During cold soaking there is uncontrolled saving in cost can be achieved. With this object activity by various types of bacteria which invari­ inview, vapour-phase soakin7 using cold water ably accompany the uncleaned paddy into the was triet:l. This method elimmated the foul odour soaking tanh. During the soaking these bacteria due to bacterial activaty but could not suppress develop on the leachate material from the paddy the loss due to metabolic activity. lhe time mentioned above and cause heavy fermentation. taken was also more:: - not less than 36 hours. So The fermentation by an aerobic organism results the authors tried vapour phase soaking at higher in disintegration of proteins which impart a foul temp~rature using open steam Soaking and par· odour to the parboiled rice. Besides, the aerobic boiling of paddy could be achieved in ahout half bacteria causes a break-down of the kernel itself an hour by oren steammg for 20 minutes and and thereby bring in a further loss. pressure treatment at 25 p5i for five minutes.

iii) Cold soaking is time consumi ng Even When this quick vapour phase soaking was ------•Resea1ch Engineers and Chemist, Paddy Proce ssin~ Research Centre, Modern Rice Mill, Tuuva rur (T.N.) Respectively

28 successfn lly achieved, the authors felt that it could tough and resistant kernel. The husk was practi­ be shortened by us mg higher pressure for shorter cally dry. The paddy conld be shelled withm ten periods such as ten minutes at 20 psi and five minutes of discharge. The colour was light minutes at 25 osi. The results indicated that yellow as the period of heat treatment was short. vapour phase soaking could be attained very quic­ There was no inter-granular moisture. This kly if steam at an adequate pressure was applied. reduced the drying effort. The paddy moisture When steam was applied at 30 psi, the parboiling was only 19 percent and the kernel moisture was could be done wic hi n te1 minutes on dry raw 20· 5 percent. The drying time using mechanical paddy without the use of any water for soaking. dryer was reduced considerably. The total cost The authors tried out a number of bate::hes of o( steam used was also reduced by this method. paddy Co-25 one tonne on the pilot plant using As there was no wetting, the leachate lo~s is tot­ the above procedure. ally eliminated and the need for water for par­ boiling was completely avoided. The out-turn Experimental Method per batch went up. This, was perhaps due to two factors : (i) Leachate loss was totally eliminated, Dry raw paddy in one tonne batches was fed (ii) More paddy was fed to a tank of a given into the pressure parboiling tank. The feed valve capacity as most of the space normally occupied was tightly closed. Open steam was let into the by the water needed for soaking was occupied tank until it started escaping through the top and by the paddy which raised the out-turn per batch. hottom steam exhaust pipes. This ensured quick The yield of brown rice was usually about and uniform penetra tion of steam and heat. The 73-75%. exhaust valves we re both closed and steam at 50· 75 psi was Jet 1n, until the p i< ddy mass in the The oil content of the bran produced from tank.was subjected to 30 psi and the temperature this method was also high (above 30%). This rose to 138 <' C. The steam inlet valve was then bran kept very well as the process stabilized the closed and the paddy was maintained at 30 psi bran. On several trials it observed that there for ten min~tes with careful adjustment of the was , an increase of only I% in the free fatty acid steam inlet valve to ensure uniformity of tempe­ content after normal storage for 20 days. rature and pressm e. During this ten minutes both the vapour phase penetration of moisture Acknowledgement and parboilmg we re achieved. At the end of the ten minutes treatment, the exhaust valves were The authors herewith desire to express their opened and the p ress ure was a1lowed to drop to gratitude to Prof. V. Subrahmanyan, Project 15 psi and the parboiled paddy was discharged at Head, Paddy Processing Research Centre, 1 iru­ that pressure. varur for the encouragement given by him and his guidance and leadership in this line of work The paddy subjected to this treatment was at all stages. completely and uniformly parboiled and has a

Vol . XI, No . 5-6 29