September, 1920 



BETTER FRUIT 



Page 5 



Observations On the Evaporation of Prunes 



From Investigations Made by C. I. Lewis, F. R. Brown and A. F. Baras for the Oregon Agricultural College 



IN the evaporation of prunes certain fruit is thoroughly heated, then the aim is entirely different. We are really 

 terms are generally used which may humidity should be gradually decreased after a cured fruit. While it may be 

 not be well understood by growers until it is a little less than the percent- desirable so to handle the evaporator 

 who are engaging in the work for the age of moisture desired in the finished that a high-class product may be turned 

 first time. A brief definition of these product. It is well to have the tunnels out in the shortest time, yetwemustnot 

 terms will probably prove helpful to thoroughly heated before the fruit is make the mistake of attempting to 

 such people. "Drying time" is figured introduced. Some growers claim that evaporate the prunes so rapidly that 

 from the time the fruit is placed in the they start prunes at as low a tempera- an inferior product is the result. Cer- 

 heating chamber to the time it is re- ture as 90 to 115 degrees. We doubt, tain changes are taking place in the 

 moved as dried fruit. "Weight per however, the wisdom of such a prac- prune during the process of evapora- 

 bushel" refers to the number of pounds tice, for with such temperatures rapid tion. Sugar is forming rapidly and will 

 of dried fruit from sixty pounds of fermentation of fruit may take place, do so unless the temperature is forced 

 fresh prunes. "Size" refers to the nuni- which means a loss of sugar and a de- too high on the one hand, or allowed 

 ber of dried prunes it takes to make a terioration of the product. Certain to remain too low, on the other. It is 

 pound, such as 30-40's, 40-50's, etc. "Dy- molds may form at the lower tempera- very important to have all the factors 

 ing percentage" is the relative amount ture and brown rot can work under influencing drying under the complete 

 of dried fruit that is obtained from a such conditions. We have not carried control of the operator and influenced 

 given amount of fresh fruit. "Dobies" on sufficient experimental work to stale as little as possible by outside condi- 

 are prunes which dry more slowly than arbitrarily just what temperatures are tions and climatic changes, 

 most of the fruit on the tray and have always best, but our results do show, Weather exerts a marked influence 

 to be re-dried. "Bloaters" are prunes and our observations with many grow- on the weight of the fruit obtained from 

 which puff up until the skin becomes ers indicate, that the temperatures we each bushel and on the drying percent- 

 very tight so that they often explode have advised produce splendid results, age. The influence of weather is well 

 and are worthless, examination show- It must be remembered that warm air shown in Table I. 



that nothing is left but skin and pit. will absorb more moisture than cold TABLE t._weight of fruit as influ- 



They are apt to have a burned or air; that if you have a large volume of enced by climatic conditions. 



scorched flavor. "Dripping" refers to hot, dry air, moisture that is given oft' We r ig hu D r y '/w 



an accumulation of thick sirup which from the fruit will be absorbed very car pe Lbs"' ""age ' 



oozes from the fruit during the process rapidly. Just how much moisture the 1911— Rainy 17.00 SHS 



of evaporation, generally caused by air can hold and still be of value in i9 13 _ D f^ ].:'..'..'.'.'.'.'.'.'.'..'. 20^0 33^3% 

 using unripe fruit and by improper prune drying, is a subject needing much Maximum in experimental 

 methods of evaporation. Too high a tern- investigation. Many tunnels are so 19 ^R a f f n r y 191 . 3 ;; V ; ; ; ; | ; ; \*jfi 28.11% 

 perature at certain stages of evaporation long that the air when it reaches the Maximum in experimental 

 may be partly responsible. Poor ventila- end of the tunnels is practically value- A ™ a r * f f ° r r \ 9 ^ ^jkiher '. '. 17.02 ll'.lit 

 tion is also a factor. "Sweating" refers to less for evaporating purposes, as it is Average for dry weather — 20.09 33.49% 

 the placing of prunes in piles or bins practically saturated with moisture, and L ° ss due t0 rain y weather.. 3.07 5.12% 

 and allowing them to remain until the giving out moisture rapidly into the The seasons of 1911 and 1914 were 

 entire mass has a uniform moisture air tends to cool it and thus reduce the much alike. They were both rainy at 

 content. "Sugaring" refers to the ac- moisture-holding capacity. As the the beginning of the season and strong 

 cumulation of a white or sugary sub- prunes are nearing the time when they southwest winds prevailed. Such con- 

 stance on the outside of the fruit, are ready to be taken from the trays, ditions are unfavorable to the evapora- 

 "Frogs" are cured prunes which are they gradually become hot. If, how- tion of prunes. During the seasons of 

 very much mishappen, probably due to ever, they are allowed to become too 1912 and 1913, however, almost ideal 

 the fruit being unripe. "Processing" hot before they are really finished, the climatic conditions prevailed for good 

 refers to the steaming of the prunes cells may rupture and leak, and drip- evaporation. The average sugar content 

 just before they are packed in the boxes ping will take place. for 1913 was 15.28 per cent and that of 

 for market. It is a cleansing, softening Thermometers. Much of the poor 1914, 12.45 per cent. This will account 

 process and facilitates proper packing, work in evaporation of prunes is due for some of the difference in weight of 

 Buildings for Evaporating Prunes. No to the fact that the grower is using a prunes, the remaining difference pro- 

 hard fixed rules can be formulated poor thermometer. Cheap thermometers bably being due to weather conditions, 

 which will apply in detail to all build- should not be used in prune evapora- From our investigations extending over 

 ings used for the evaporation of prunes, tion. It would pay all growers to use a number of years, we find that there 

 Every grower must study his own some self-recording thermometer which j s a loss ranging from five per cent to 

 evaporator carefully, so that he may would record the temperature during the nine per cent in the drying percentage 

 know under what conditions he can entire twenty-four hours. Such a ther- due to unfavorable weather conditions, 

 secure certain temperatures, certain air mometer will easily indicate what hap- if climatic conditions had been such 

 circulation, and a combination of fac- pens when the night worker goes to that the prunes had thoroughly matur- 

 tors which will turn out a high-grade sleep, and will be an aid in explaining e d, having a very high sugar content, 

 fruit. What might apply to one build- many of the poor results obtained. less time would have been required to 

 ing might not to another. There are Air circulation is extremely import- dry, there being a high drying percent- 

 certain fundamental principles, how- ant. Good air circulation and proper a g e . This is one reason why Petites 

 ever, that apply to all buildings. For ventilation must prevail at all times. It dry more quickly than Italians; another 

 instance, lack of ventilation or air cir- is possible to have too rapid circulation reason is because they are a smaller 

 culation would have the same effect re- and to have the ventilators draw out fruit. Investigations will show that 

 gardless of where the prunes are dried, the air too quickly. For example, in some years prunes contain much more 

 The use of abnormally low, or abnorm- evaporating vegetables, it is very de- moisture than others, are less mature 

 ally high temperatures would have the sirable to have the air move rapidly at and contain less sugar, and therefore 

 same influence in any building, as far a relatively low temperature of about require a longer drying time, 

 as the type of product turned out is 140 degrees. These results are obtained Moisture Content. The question is 

 concerned. Prunes require a great deal by blowing air over steam pipes and often asked as to how much moisture 

 of air, which should move at the rate causing it to move rapidly over the prunes should contain after they are 

 of at least 600 feet a minute. They vegetables. Some fresh fruits should be evaporated. In our experimental work 

 should have a starting temperature of , dried in this same way. The aim is to we have accepted seventeen per cent to 

 about 130 to 145 degrees, and a finishing have the product when finished re- eighteen per cent as the proper moisture 

 temperature not higherthan 160 degrees, semble, as much as possible, the undried content. In some cases it has run as 

 A high humidity should prevail until the product. With prunes, however, the Continued on page 29. 



