PNITEBSITY OF CALIFORNIA PUBLICATION COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA THE EVAPORATION OF GRAPES BY W. V. CRUESS, A. W. CHRISTIE AND F. C. H. FLOSSFEDER BULLETIN No. 322 June, 1920 UNIVERSITY OF CALIFORNIA PRESS BERKELEY 1920 David P. Barrows, President of the University. EXPERIMENT STATION STAFF HEADS OF DIVISIONS Thomas Forsyth Hunt, Dean. Edward J. Wickson, Horticulture (Emeritus). Walter Mulford, Forestry, Director of Resident Instruction. Herbert J. Webber, Director Agricultural Experiment Station. B. H. Crocheron, Director of Agricultural Extension. Hubert E. Van Norman, Vice-Director; Dairy Management. James T. Barrett, Acting Director of Citrus Experiment Station; Plant Pathology William A. Setchell, Botany Myer E. Jaffa Nutrition. Charles W. Woodworth, Entomology. Ralph E. Smith, Plant Pathology. J. Eliot Coit, Citriculture. John W. Gilmore, Agronomy. Charles F. Shaw, Soil Technology. John W. Gregg, Landscape Gardening and Floriculture. Frederic T. Bioletti, Viticulture and Fruit Products. Warren T. Clarke, Agricultural Extension. John S. Burd, Agricultural Chemistry. Charles B. Lipman, Soil Chemistry and Bacteriology Clarence M. Haring, Veterinary Science. Ernest B. Babcock, Genetics. Gordon H. True, Animal Husbandry. Fritz W. Woll, Animal Nutrition. W. P. Kelley, Agricultural Chemistry. H. J. Quayle, Entomology. Elwood Mead, Rural Institutions. H. S. Reed, Plant Physiology. L. D. Batchelor, Orchard Management. J. C. Whitten, Pomology, t Frank Adams, Irrigation Investigations. C. L. Roadhouse, Dairy Industry. R. L. Adams, Farm Management. F. L. Griffin, Agricultural Education. John E. Dougherty, Poultry Husbandry. L. J. Fletcher, Agricultural Engineering. Edwin C. Voorhies, Assistant to the Dean. fin co-operation with office of Public Roads and Rural Engineering, U. S. Department of Agriculture THE EVAPORATION OF GRAPES BY W. V. CRUESS, A. W. CHRISTIE, and F. C. FLOSSFEDER CONTENTS PAGE I. Purpose of Investigation 421 II. Acknowledgments '. 422 III. Principles of Evaporation 423 (a) Necessity of Heat 423 (6) Modes of Conveying Heat 424 (c) Necessity of Air Circulation 424 (d) Humidity Control 425 (e) Miscellaneous Requirements 427 IV. The University Farm Evaporator 428 (a) List of Materials and Cost of Construction 428 (6) Description of the Evaporator Used in 1919 430 (c) Course followed by Grapes at Evaporator 434 id) Suggested Revisions in Plan of University Farm Evaporator 436 V. Cost of Operation 441 VI. Results of Investigations 442 (a) Dipping 442 (6) Sun Drying vs. Evaporation 447 (c) Sulfuring 450 id) Effect of Temperature on Quality and Rate of Drying 451 (e) Effect of Construction of Trays 452 (/) Comparison of Gravity and Air Blast Burner 455 ig) Comparison of Disc and Multivane Fans 456 ih) Exhaust vs. Positive Blower Fan 458 ii) Recirculation of Air 459 ij) Direct Use of Gases of Combustion in Drying 461 ik) Moisture Content of Evaporated Grapes 463 (Z) The Determination of Humidity 465 (m) Measurement of Air Velocity 467 in) Experiments on Stemming, Seeding, and Packing 467 VII. Summary 469 I. PURPOSE OF THE INVESTIGATION Drying has proved to be one of the most feasible methods of converting the wine grapes of California into a non-perishable salable product. In the hot interior valleys, where the grapes ripen early, the fruit may be dried successfully on field trays in the vineyard. 422 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION However, at least 50 per cent of the wine grapes are grown in regions where the grapes ripen so late that sun-drying can not be safely undertaken, because of the danger of loss through early fall rains. In the raisin-growing districts, serious loss from early rains to Sul- tanina and Muscat grapes on drying trays has occurred several times during the past ten years. Some provision should also be made for utilizing the second-crop Muscat grapes which in former years have been sold to wineries and distilleries. These grapes ripen too late in the fall to permit of drying them in the sun. In the aggregate, they amount to many thousand tons, and formerly were a source of con- siderable revenue to the raisin growers. The cull Tokay and other cull table grapes from the packing houses and the inferior bunches left on the vines have been used principally for wine making in past years. Much of the brandy used in the manufacture of sweet wine was made from this cull fruit and resulted in a small return to the grower. It is contended by many that a greater yield and a better quality of raisins are obtained by artificial drying in an evaporator than in the sun. Because of these important reasons it is imperative that there be available for producers of all varieties of grapes reliable information on the construction and operation of evaporators for the drying of raisin grapes, wine grapes, cull table grapes, and second-crop Muscats. The investigations recorded in this publication were carried out for the purpose of obtaining such information. While the magnitude of the problem has made its completion in the one season's time devoted to it impossible, we believe the results obtained to date are sufficiently important and conclusive to warrant their publication. Most of the data reported were obtained in the commercial evaporator at the University Farm, Davis, although a great many small-scale experiments were made in our experimental evaporators at Berkeley. II. ACKNOWLEDGMENTS The erection of an evaporator of commercial size was made possible by a grant of $2500 from the State Board of Viticultural Commis- sioners with which the equipment and most of the building materials for the evaporator were purchased. Through the courtesy of Dr. J. C. Whitten of the Division of Pomology, a portion of the Deciduous Fruits Appropriation passed by the last State Legislature was applied in the employment of a Bulletin 322 THE EVAPORATION OF GRAPES 423 chemist who cooperated in carrying out the investigations. "Without these two special funds very little investigational work could have been performed. The writers wish to thank Professor F. T. Bioletti for the valu- able suggestions given during the planning and construction of the evaporator and during the investigations. III. PRINCIPLES OF EVAPORATION The construction of evaporators and the discussion of the experi- mental results will be better understood if the more important prin- ciples and previously existing data on fruit evaporation. Evaporators of many types have been used with varying degrees of success for many years. From the experience gained in the use of these evapor- ators and from observations and measurements taken by scientific investigators certain principles have become recognized. To this exist- ing knowledge new information is being constantly added and some of the older theories are being discarded or seriously modified. (a) NECESSITY OF HEAT Evaporation of fruits involves the change of water from the liquid to the vapor state. This change requires the expenditure of a very definite amount of heat regardless of the system of evaporation and the temperature used. This quanitity of heat is known as the "latent heat of vaporization" and is equal to the amount of heat given off when steam condenses to water. Expressed in the usual heat-unit terms, approximately 965 British Thermal Units of heat are required to evaporate one pound of water. A British Thermal Unit (B. T. U.) is the amount of heat used in raising one pound of water one degree Fahrenheit. To the heat actually used in evaporation must be added that needed to raise the fruit from its original temperature to that of the evaporator. This ordinarily amounts to 50 to 75 B. T. U. per pound of fruit; thus making the total minimum quantity of heat necessary slightly above 1000 B. T. U. per pound of water evaporated. The fuel efficiency of an evaporator may be judged by its approach to this minimum in its heat requirements. If the drying ratio of the fruit, the weight of fruit evaporated, the quantity of fuel consumed, and the heat value of the fuel are known, the heat efficiency of the evaporator may be calculated. In most evaporators it will be found that not over 50 per cent of the heat generated in the furnace is 424 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION utilized in drying the fruit because of the heat lost by radiation and leaks in the evaporator and the heat lost in the exhaust air. This last loss is the greatest. A typical case will show its magnitude. If the outside air at 80° F. is heated to 160° F., as it enters the evaporator, and if it leaves the evaporator at 120° F., it is readily seen that only 40° F. of the 80° F. rise in temperature is utilized, or less than 50 per cent of the heat is utilized in drying, if we include radiation and other minor losses of heat. Many evaporators have failed because they have not been supplied with sufficient heat. The air heating system must have adequate capacity and should supply an abundance of heat without the need of forcing the furnace. The attempt to force the furnace beyond its capacity has been a very common cause of loss of evaporators by fire. (ft) MODES OF CONVEYING HEAT Heat may be applied or conveyed to the fruit in several ways. It may be conducted by direct contact of the fruit with the heating system. This method of conveying the heat has not been used in practice to any appreciable extent because the high temperatures of the heating element would scorch the fruit. In European countries community bake ovens are often used for drying fruits after the bread has been removed, the fruit in many cases resting in contact with the hot bricks of the oven. Heat may to a limited degree reach the fruit by radiation, just as heat is radiated into a room from a fire place or stove. In the stack and tunnel types of evaporators it is probable that this mode of heat transfer is of appreciable importance but in the average air- blast type of evaporator it is negligible. By far the most important method of heat transfer is by air currents, which may, if we use the term rather loosely, be termed ''transfer of heat by convection." The air is heated by contact with a furnace, radiating pipes, or other heating system, and the heated air rises through the drying compartment because it is lighter than the outside air or it is transferred over the fruit to be dried by means of a fan. (c) NECESSITY OF AIR CIRCULATION Since a large amount of heat is essential for successful drying and since air is the usual vehicle for transfer of this heat from the furnace to the fruit the necessity of air circulation in the evaporator Bulletin 322 THE EVAPORATION OF GRAPES 425 can be seen. Just how important this factor is, may be seen from the following consideration. It will require approximately 63,000 cubic feet of air dropping one degree Fahrenheit to furnish 965 B. T. U., the heat necessary to evaporate one pound of water ; or it will require approximately 1575 cubic feet of air dropping 40° F. to furnish this amount of heat. A 40° F. drop in temperature is probably greater than that taking place in the average evaporator; consequently, 1575 cubic feet of air per pound of water evaporated may be considered in the nature of the minimum air requirement. An evaporator holding 5 tons of grapes which dry in 24 hours and which have a drying ratio of 3:1 must evaporate 6666 pounds of water per 24 hours, or 4.6 pounds per minute. This will require a minimum of 4.6X1574 = 7245 cubic feet of air per minute. If the drying period is 12 hours, approximately 14,500 cubic feet of air per minute will be needed. A few evaporators have during the past season dried wine grapes in twelve hours but twenty-four hours time or longer was required in most cases. In our small evaporator at Berkeley which was supplied with an excess of air, grapes were dried in from six to twelve hours, indicating the possibilities of reducing the drying period of grapes by increasing the air supply, which means also increased heat supply. (d) HUMIDITY CONTEOL Air circulation is also important as a means of carrying away the moisture evaporated from the fruit by the heat. In a "dead air" space, heated fruit for a short time rapidly gives up its moisture to the surrounding air which soon becomes saturated and further evaporation ceases unless the saturated air is replaced by fresh dry air. The moisture-carrying capacity of air is relatively limited ; hence, a large volume of air must pass over the fruit to carry away the moisture if drying is to be continuous and rapid. A rough conception of the amount of air needed for this purpose under average conditions may be had from the following consideration. At 101° F., approximately 350 cubic feet of air at the saturation point is required to carry one pound of water. At 128° F., this same volume of air will hold at saturation two pounds of water vapor, and at 155° F., four pounds of water vapor; that is to say, each 27° F. rise in temperature will double the moisture-absorbing power of the air. At 120° F., 350 cubic feet of air will absorb about 1% pounds of water vapor. 426 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION These figures refer to air saturated with moisture vapor; that is, air of 100 per cent relative humidity. Relative humidity may be defined as the percentage of saturation of air with water vapor, although the condition applies also to a space which may be free from air. In most commercial evaporators, however, we are dealing with air. Few evaporators raise the relative humidity of the air above 50 per cent. If the air leaves the evaporator at 50 per cent relative humidity and at 120° F., it will carry approximately 1% pounds of water vapor per 350 cubic feet or each 1000 cubic feet will carry approximately five pounds of moisture. For an evaporator drying 5 tons of grapes per 24 hours, approximately 5 pounds of water must be removed from the grapes per minute, or at least 1000 cubic feet of fresh air must be drawn through the evaporator per minute to carry away the moisture. In the above calculations to determine the amount of air necessary to carry the required amount of heat to the fruit it was found that approximately 7245 cubic feet of air per minute was required. Com- paring this result with the amount of air needed to carry away the moisture we find that about seven times as much air is needed to fur- nish heat for evaporation as is necessary to carry away the water evaporated by this heat. If this extra six-sevenths of the air is allowed to escape, much fuel value and much of the moisture-carrying capacity is wasted. If six-sevenths of the air under the above assumed condi- tions be returned to the furnace room and mixed with one-seventh of fresh air and if one-seventh of this mixture after reheating and passage through the evaporator be allowed to escape at 50 per cent or greater relative humidity it is readily seen that the efficiency of the evaporator is greatly increased. This recirculation of the air is not only theoretically more efficient but is of great value in practice for other reasons. If the air is too dry and of high temperature, moisture may be taken from the surface of the fruit more rapidly than it can effuse from the interior, resulting in the formation of a hard shell on the surface, or ' ' case hardening, ' ' which retards subsequent evaporation. If the humidity of the air is relatively high, diffusion keeps pace with evaporation and case harden- ing is prevented. A second advantage of the higher humidity of the air is in preventing the over-drying of fruit ; because drying will cease when the fruit and air arrive at the same relative moisture content. Grapes tend to dry unevenly and many to over-dry in an atmosphere of very low humidity ; that is, in very dry hot air. A third advantage of the higher humidity is its tendency to reduce the injurious effects Bulletin 322 TH e evaporation OF grapes 427 of high temperatures on the fruit flavors. It is therefore possible to use higher temperatures of drying with humid air than with dry air. Because of the vital importance of controlling the humidity of the air used in drying, prospective purchasers and manufacturers of evaporators are advised to install in their plants some means of effect- ively regulating the moisture content of the air. One of the most effective methods of increasing the humidity of the air to the desired degree, is that of returning a part of the exhaust air from the evaporator to the furnace room where it is mixed with fresh air, reheated and passed over the fruit again. By varying the propor- tion of the recirculated air any desired degree of humidity may be maintained. As already pointed out, recirculation of a part of the air results in a great saying of fuel. By way of summary it may be stated that (1) evaporation of water from a free surface varies inversely as the relative humidity, (2) directly as the time, (3) directly as the temperature, and (4) as the square root of the air velocity. Dipped grapes more nearly approach a free surface of water than do most fruits, because of their small size and, therefore, the above relations will probably be more nearly true for grapes than for other fruits. (e) MISCELLANEOUS REQUIREMENTS In addition to providing for the fundamental requirements of adequate heat supply, air circulation and control of humidity, the evaporator to be thoroughly satisfactory should include the following features : It should utilize its fuel efficiently. This means that the. transfer of heat from the furnace to the air should be as complete as possible, with very little of the heat escaping through the smoke stack. It also means that radiation losses and losses through leaks should be minimized. The evaporator should be as convenient^ arranged as possible in order to reduce labor costs to a minimum. This is a very important point that some manufacturers have overlooked. Frequent shifting of the trays in some evaporators greatly increases the labor cost: a practice made necessary by uneven air distribution in the evaporator and uneven drying of the fruit on the trays. The evaporator should be so arranged in relation to the dipper, spreading tables, sulfur house, stemmer, storage bins, etc., that the fruit can be handled efficiently at all points. This will require careful arrangement of the plant. 428 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION It is the opinion of the writers that all evaporators representing any considerable investment should be of fireproof construction. The slight extra cost is an excellent investment. The cost of an evaporator for grape drying must not be excessive if the investment is to prove profitable. On the other hand, the evaporator should not be of such cheap construction that its period of usefulness will be excessively short. At 1919 prices for materials, it is believed that a substantially constructed evaporator similar in design to the University Farm Evaporator described below can be erected and equipped for about $500 per fresh ton capacity per 24 hours. IV. THE UNIVERSITY FARM EVAPORATOR This evaporator was constructed primarily for the purposes of conducting investigations in the drying of grapes and other fruits upon a commercial scale and to convert the grape crop of the Univer- sity Farm into a marketable product. It was also hoped that the evaporator would serve as a model for growers who might wish to build evaporators. The discussion of the evaporator has been taken up under the following topics: List of Materials and Cost of Construction, Descrip- tion of the Evaporator as Used in 1919, Course Followed by Grapes at Evaporator, and Suggested Revisions in Plan of University Farm Evaporator. (a) LIST OF MATEEIALS AND COST OF CONSTEUCTION The materials, labor, and equipment entering into the construction of the Davis evaporator are given in the following list : Lumber : 6" X 6" rough redwood 152 2" X 6" S-2E Oregon pine 950 1" X 6" pine sheathing 3500 2" X 4" S-4-S Oregon pine 400 2" X 4" rough pine for yard track 360 1" X 4" T & G flooring 4100 2" X 8" rough pine 82 4" X 6" rough pine 88 4" X 4" rough pine 64 4" X 4" S-4-S Oregon pine for dipper 8 3" X 4" S-4-S Oregon pine for dipper 20 2" X 3" S-4-S Oregon pine for dipper 8 2" X 12" rough pine 300 19,000 redwood shingles linear feet $679. Bulletin 322 THE EVAPORATION OF GRAPES 429 2. Labor: 137% days at $5.00 per day 687.84 3. Plumbing materials for water and fuel supply 28.33 4. Electrical equipment and supplies: (a) 1 7% h.p. 3-phase, 110-volt motor for fan $188.80 (b) 2 transformers, complete 97.50 (c) Wire 117.72 (d) 2 poles 18.80 (e) Switches, light sockets, insulators, cross arms, fuse plugs, etc 25.95 448.77 5. Hardware: (a) Heating pipe, 12" riveted: 6 pieces 8' long, 2 pieces 1' long, 2 pieces 20' long, 6 return bends, and 2 elbows $135.00 (b) 2 old boiler shells, 6' X 3' 100.00 (0) 1 California-Fresno large size gravity burner 22.50 (d) 1 Johnson whirlwind distillate burner, medium size .. 85.00 (e) 1 54" disc fan (American blower) 182.00 (/) 1 60" disc fan (American blower) 239.70 (g) 1 50-gallon cauldron '.'. 25.00 (h) 2 22" prune dipping baskets 17.00 (i) 1 set roller bearings for dipper 17.50 (j) 250' iron T-rail, 8 pounds per yard 39.57 (1c) 3 all steel lower dry-yard transfer trucks 56.25 (1) 13 wooden frame dry-yard trucks 73.13 (m) Hinges, nails, wire washers, furnace doors, etc 35.71 1028.36 6. Materials for 500 trays: (a) Shook: 1000 pieces, 1%" X 1%" X 36"; 1000 pieces, %" X iy 2 " X 33"; 1000 pieces, %" X 1%" X 36"; 1000 pieces, %" X %" X 33"; 500 pieces, %" X 1" X 33"; 500 pieces, %" X %" X 34"; 1000 pieces, 1" X iy 2 " X 36" for side cleats to raise height of trays $90.00 (6) Wire: 1200 linear feet, y 2 " mesh; 300 linear feet, %" mesh; 300 linear feet, %" mesh 253.45 343.45 7. Cement, bricks, etc.: (a) 128 sacks of cement $147.34 (b) 1000 second-hand brick (no charge) (c) 400 fire brick 32.00 (d) 160 pounds of fire clay 4.80 (e) 3 loads of crushed rock 6.00 (/) 4 loads of sand 8.00 (g) 17 loads of creek gravel (no charge) (h) 1^ barrels of lime 4.50 202.64 8. Paint for roof and stacks 41.75 430 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 9. Thermometers: (a) 1 recording thermometer $52.50 (&) 2 angle-stem Fahrenheit thermometers 39.60 92.10 10. Belting: (a) 25' of 4" rubber belting (estimated) 13.25 (&) 10' of 4" leather belting, second hand (estimated) .... 10.00 (c) Belt lacing 25 23.50 11. Miscellaneous 5.91 Total $3582.64 The cost of an evaporator of this capacity (6 tons of fresh fruit per charge) to the average builder at 1919 prices for materials would be considerably less than the total given above for the following reasons. The furnace room is twice as large as necessary and the outside walls were given a special finish. One furnace and one burner were found to be sufficient, although for experimental purposes two of each were installed. The shed above the evaporator was built very substantially of such design and finish as to compare favorably in appearance with other buildings on the University Farm. A shed less attractive in appearance but equally serviceable would probably be built by the average grower. One fan was sufficient, although for experimental purposes two were installed. However, these fans were of an inexpensive type and one multivane fan to replace them would cost as much as the two disc fans actually installed. The sulfur house was built of cement; a wood sulfur house will answer. Taking all such possible savings in cost into account it is believed that an evap- orator of the same design and capacity as our plant could be built and equipped for about $3000, or at a cost of about $500 per fresh ton capacity per charge. (6) DESCRIPTION OF THE UNIVERSITY FARM EVAPORATOR USED IN 1919 The evaporator consists of a tunnel through which the cars loaded with fruit are moved during drying and a fire-proof furnace room for heating the air which is drawn or blown through the tunnel by a fan. The remaining equipment is used for preparing the fruit for drying or for packing the dried product. The drying tunnel and dipping outfit are housed beneath a shed approximately 60 feet long and 20 feet wide. The general appearance of the complete plant may be seen from the accompanying photograph. Bulletin 322 THE EVAPORATION OF GRAPES 431 The tunnel is 33 feet long by 7 feet high by 6y 2 feet wide, inside dimensions. The walls and ceiling are constructed of 1" X 4" tongue and groove pine on an outside framework of 2" X 4" pine. The floor is of cement and slopes toward the furnace room to aid in moving the cars forward. The slope is 14 inch per foot ; for the type of cars used, this slope could be considerably increased to advantage. The location of the two doors may be seen from the accompanying sketch. The door openings are 7 feet high by 64 inches wide and each is closed by two tight-fitting folding doors. Transfer tracks enter each door and connect with the tunnel track. The transfer track rails are 42 inches apart and are ordinary dry-yard T rails of 8 pounds Fig. 1. — View of the University Farm Evaporator. per yard weight. The tunnel track rails are set 24 inches apart and connect with the transfer tracks at each end of the tunnel. An air return flue 1 foot high by 6y 2 feet wide and 33 feet long rests above the drying tunnel. This connects with the tunnel outlet by a door 1 foot by 6y 2 feet which folds upward and by a door of the same size in the furnace room. The return flue is constructed of 1" X 4" tongue and groove over 2" X 4" pine. It is used for the return of a part of the exhaust air to the furnace room where it may be mixed with fresh air, reheated, and recirculated. The tunnel connects with the furnace room through a 60-inch disc fan. A 54-inch disc fan is located at the other end of the tunnel. A 7% h.p. electric motor is used to operate either fan. The fans and motor have pulleys of such size that the 60" fan is operated at 300 r.p.m. and the 54-inch fan at about 350 r.p.m. When operated at 432 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION the above speeds either fan should deliver 25,000 cubic feet of air per minute (catalog rating). The two fans were installed merely for the purpose of comparing a blast fan with a suction fan. The furnace room is 16 feet long by 12 feet wide by 12 feet high, outside dimensions. The walls and roof are of 6-inch reinforced con- crete. Two old boiler shells, each 6 feet long by 3 feet in diameter, open at one end for installation of burner, and connected at the other end to a 12-inch pipe, have been placed on opposite sides of the furnace room, as shown in figure 2. Each furnace is connected to three lengths of 12-inch heavy gauge sheet iron pipe which is led back and forth above each furnace before connecting to the smoke stack extending 20 feet above the furnace room. The hot gases from the furnace must travel a distance of 40 feet through the radiating pipes in the furnace room before reaching the stack. One furnace is fitted with a gravity burner and the second with an air-blast burner. Fuel is supplied to the burners through ^-inch pipes connected to a 110- gallon distillate drum placed on a platform 5 feet above the ground. In the wall of the furnace room opposite the tunnel are located two sets of three doors each for the admission of fresh air to the furnace room and tunnel. One set of doors is opposite each furnace. Each door is about 28 inches by 20 inches in size. (See figs. 1 and 2.) The amount of air admitted to the evaporator is regulated by adjust- ing these doors. The dipping equipment is located under the east end of the evaporator shed. It consists first of a 50-gallon prune-dipping cauldron mounted over a brick furnace in which is burned coal or wood to keep the lye solution in the kettle at the boiling point. Adjacent to this kettle and at the same height above the floor (33 inches) is a cement vat of the same size and shape as the cauldron. This vat holds the water used in rinsing the grapes after dipping, and is equipped with a drain pipe and fresh water supply. The dipping machine consists of the following parts. Two 22-inch prune-dipping baskets are hung at the ends of 3" X 4" pieces which are 5% feet long and pivoted on two 4" X 4" pieces, which in turn are attached to a 6" X 6" upright piece and supported by 2" X 4" pieces, as shown in figure 2 section. The 6" X 6" upright pieces rest on a roller bear- ing pivot. The baskets are counterbalanced by boxes of sand. The end of each basket support carrying the sand box is connected to a pivoted handle so that the basket may be depressed into the lye solution or rinse water by merely raising this handle. The handle is also used in swinging the loaded basket from the loading chute to the lye kettle; from lye kettle to the rinsing vat, from the rinsing Bulletin 322 THE EVAPORATION OP GRAPES 433 8 *j P rta' CO P §13. «j fcr. CD fcj s ° 5 d: p M <°£ h-» P ooorq p o « p vat to the tray loading table, and from this point back to the loading chute. This dipping machine is patterned closely after the ''Sutter County Merry-Go-Round Dipper" used for many years for dipping Sultanina grapes before drying and may be purchased in complete form from manufacturers, although the outfit is not complicated and can be built locally. The ordinary prune dippers of various forms may be used successfully, but must be equipped for rinsing the dipped grapes. Continuous dipping machines for grapes are available. 434 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION A platform. 16' X 12' and 2 feet high is placed outside the evapo- rator shed but adjacent to the dipping outfit for receiving the fresh grapes. I A concrete sulfur house, 7 feet wide by iy 2 feet high by 8 feet long, inside measurements, is located a short distance from the shed. It is equipped with tight-fitting folding doors; a 6-inch adjustable ventilator in roof ; a sulfur pit, 8 inches deep and 8" X 12" in size, and tracks for drier cars. It will hold two loaded cars. Thirteen wooden frame dry-yard trucks were used. The evapo- rator held eight cars when filled to capacity and each car held 42 trays of 35 pounds of grapes each, making a total of six tons of fresh grapes per charge. The frames on the trucks were placed at right angles to the tracks upon which the cars operate. This position of the frames makes each truck six feet wide and three feet long and therefore only one track is necessary in the tunnel. The transfer cars are of steel construction throughout and of the type used in evaporators in Fresno County in which raisins are dried for cap stemming. Both the evaporator and the transfer cars were very satisfactory, except for the difficulty in moving the cars because of the friction on the axles. Roller-bearing wheels would be much more desirable but are costly. The trays are three feet square. Each side is constructed of one piece, 36" X 1%" X 1%" and one piece, 33" X %" X iy 2 " J each end consists of one piece, 36" X %" X 1%" and one piece, 33" X %" X %"• The tray is braced through the center by one piece, 33" X %" X 1", and one piece, 34" X %" %'•' Most of the trays were made with screen bottoms held between the various pieces of shook listed above. (See fig. 9.) The most satisfactory trays were of the above construction for the frame but with narrow wooden slats substituted for the screen. Screen of 14" mesh is much better than that of V 2 " mesh. It was found necessary to raise the height of the sides of the trays by nailing to them strips 1" X IV2" X 36" in size in order to give sufficient space for passage of air. (c) COUESE FOLLOWED BY GRAPES AT EVAPORATOR The grapes were ordinarily treated as follows : The fresh grapes were unloaded at the receiving platform and weighed. They were then emptied into the chute from which they fell into the dipping basket. The basket was immersed in the boiling lye solution, which varied in strength, from y 2 per cent to 3 per cent lye according to the variety of grapes. After 5 to 40 seconds' immersion in the lye solution, the time varying with the variety, the grapes were plunged into cold water to remove adhering lye. The basket of rinsed grapes Bulletin 322 THE EVAPORATION OF GRAPES 435 was then transferred to an empty tray and the grapes spread evenly by hand. The loaded trays were stacked in two tiers of 21 trays each on a car. The loaded car was transferred to the sulfur house and exposed to sulfur fumes for about 30 minutes. In some cases sul- furing was omitted. The car of fruit then entered the tunnel at the end opposite the furnace room where the air was moister and 20 to 30 degrees cooler than at the furnace end. As each car of dried grapes Fig. 3. — Evaporator car loaded with trays of freshly dipped grapes, transfer car beneath evaporator car. Unloading slat bottom tray at right. Note was removed through the side door at the furnace end of the tunnel, the remaining cars were moved forward the length of one car, and a fresh car was inserted at the exhaust end. The dried grapes were allowed to cool and were then transferred to sacks for shipment without stemming. All of the above steps were varied greatly during the various experiments. 436 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION (d) SUGGESTED EE VISIONS IN PLAN OF UNIVERSITY FARM EVAPORATOR The evaporator in its first form proved successful. However, the past season 's experience showed that certain additions and changes are desirable in order to increase the efficiency of the plant and the convenience of operation. The sketches shown in figures 4 and 5 indicate the construction of an evaporator recommended to growers. It resembles the University Farm evaporator very closely in outline and appearance, but includes in its construction the modifications and additions noted below. Practically all of the suggested changes have been made and may be seen by those who wish to visit the University Farm at Davis. 1. Furnace Room. — One furnace, 10' to 12' long by 3' in diameter, equipped with a medium-size air-blast distillate burner is sufficient. The furnace room should be of fire-proof construction, e.g., concrete, brick, or tile and should be about 14' long by 8' wide by 11' high, inside dimensions. Attached to the furnace are nine lengths of 12-inch heavy gauge black iron pipe distributed as shown in figure 5, giving a total length of radiating pipe, including connections, of approxi- mately 120 feet. The pipes are arranged in three tiers of three pipes each. The individual pieces are joined together vertically by return bends and horizontally by headers or T connections. A T connects the smokestack to the radiating pipe system. This is fitted with two dampers by means of which the gases of combustion may be allowed to flow out through the stack or into the furnace room as desired. This arrangement of pipes and clampers gives approximately three times the heating surface furnished by the first installation for one furnace and also makes it possible to use the gases of combustion directly in drying. At each side of the furnace in the end wall of the furnace room is situated an air intake door. Each is one foot wide and one and a half feet high. Another air intake door of same size is located two feet above the furnace. All doors should be sliding to enable regula- tion of air intake. (See revised plan, fig. 5.) The evaporator now includes essentially these features. 2. Connection of Furnace Room to Tunnel. — No fan to be located between the furnace room and tunnel and the opening connecting the two to be of same size as cross section of tunnel ; that is, 7 feet high by 6V2 feet wide. 3. Fan, — The two disc fans of the present installation to be replaced by a top vertical discharge multivane fan with fan wheel Bulletin 322 THE EVAPORATION OP GRAPES 437 438 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 36 inches in diameter and connected to a iy 2 horsepower motor by belt and pulleys to give about 300 r.p.m. The fan to be located at air exit end of tunnel. Intake of fan to be connected by sheet metal housing to tunnel outlet. The discharge of fan to be connected to return flue of tunnel and also arranged to discharge into the open air as shown in figure 5 ; these two connections to be equipped with adjustable dampers so that any proportion of the exhaust air may be returned to the furnace room or discharged into the open air. This fan has now been installed. 4. Air Locks. — During the past season considerable heated air was lost and drying was interrupted when the doors of the tunnel were opened to insert or remove cars, or to enter the tunnel to take obser- vations on temperature, etc. It is, therefore, very desirable to build compartments at entrance and exit of the tunnel as shown in figure 4. In using the compartment at the entrance end of the tunnel the car of fresh fruit enters the compartment through the folding doors at the side of the compartment. The operator enters with the car and closes the doors. He then opens the sliding door connecting the air lock with the tunnel, places the car in the tunnel and closes the sliding door. Finished cars are removed in a similar manner. Practically no heated air is lost or cold air drawn in during the above operations. The air lock for entrance of fresh fruit consists of a compartment 5% feet wide, 7 feet high, and 7% feet long, inside dimensions. Two folding doors form the side of the air lock toward the dipping outfit and a second set of doors opens toward the sulfur house. The lock for removal of cars of dried fruit is of the same dimensions and con- struction, except that it is equipped with doors at the ends only. Both locks are constructed of 1" X 4" tongue and groove pine over a frame of 2" X 4" pine. These may now be seen in place at the University Farm. 5. Dipping Tank. — It was very difficult to maintain the lye solu- tion at the boiling point during the 1919 season because of the small size of the dipping cauldron, 50 gallons, and necessity of using wood or coal instead of oil for fuel. The 50-gallon kettle has been replaced by a sheet metal tank 6' long by 3' wide by 1%' deep mounted in a fire brick furnace equipped with a medium-size blast-type distillate burner. The above tank will hold about 200 gallons of liquid and presents a long surface to the furnace flame. The experience of others has proved that a furnace and dipping tank of this type can be maintained at the boiling point during continuous operation. 6. Rinsing Vat. — The present 50-gallon rinsing vat could be in- creased to 200 gallons in size to advantage. This would require less Bulletin 322 THE EVAPORATION OF GRAPES 439 frequent changing of rinse water. A sheet metal drain over the space between the dipping vat and the rinsing vat for return to the dipping vat of the lye solution which drips from the dipping basket would reduce the loss of lye solution. 7. Track System. — The track now located under the shed at the south side of the tunnel will be moved outside the shed and will o o o 1- nc/rriN6 pipcs OOD ruKKftCC FUffNflCL ROOM C/?035 SECT/ON S< >/V OTW «, rURNF\CE ROOM & »vwess LONGITUDiMftL SECT/Ort scale or r£c r ^ * > *v o ' k ' 4 ' 6 ' 8 ' to ADJUSTABLE. vre ncTTucX ■ S5E B5£ » CO/vc/?£rre Z.y£Z KE.TTLEL WNG/TUD/NflL SECTION £ < i rt yye/i/vsrc i 7-ftactK IKETC/iEO j3Y V /■ C/ft/fSS. MUL-TIV/lrtE: EXH/1U5T /7?/y //vs r^z.4. /? r/o/y if: * »*v Fig. 5. — Sections showing fan connections, lye tank, and furnace room, of revised University Farm evaporator. connect to two transfer tracks as shown in figure 4. This track will be continued to the west end of the shed where it will connect to a transfer track which in turn connects to the track between the dipping outfit and tunnel entrance. This arrangement will make it possible to move loaded and empty cars to and from the tunnel without inter- ference. 8. Observation Windows. — Six or seven small port holes about one foot square have been cut in the north wall of the tunnel at such points that each car of fruit in the tunnel may be observed and samples removed. The windows are closed by air-tight doors. 440 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 9. Double Walls for Tunnel. — The first tunnel walls were made of one thickness, 1" X 4" T & G over 2" X 4" pine outside frame. The frame has been covered with T & G over building paper, to make the walls airtight and to reduce radiation losses. 10. Tray Guides on Trucks. — Difficulty was encountered during the past season in holding the trays on the trucks in a perfectly vertical position. Upright guides of 2" X 4" have been placed in the Fig. 6. — Photographs of an evaporator truck equipped with upright guide-posts for trays. center of each car frame and the trays will be stacked against this frame. The tunnel is wide enough to permit this change. See figure 6 which illustrates such a car used in the Pearson evaporator. 11. Trays. — Most of the screen bottom trays will be converted into slat bottom trays by replacing the screens with narrow wooden slats placed about % of an inch apart. The sides of all trays will be increased in height by the addition of pieces 36" X 1" X 1%" to trays not already so equipped. 12. Air Baffles. — To prevent the passage of heated air beneath the cars during the past season pieces of canvas were nailed to the car frames. These extended from the level of the track to the bottom of the cars. These will be replaced in part by two enclosed wooden platforms on the tunnel floor, one on each side of the tunnel track, Bulletin 322 TH e EVAPORATION OF GRAPES 441 of such height that the frames of the trucks will barely clear them. These platforms will be closed so that the air will not be permitted to flow beneath the car frames between the tracks and walls of tunnel. The canvas will be retained on the car frame between the tracks only. It is essential that all possible precautions be taken to force the air to flow over the trays. Air, like water, follows the channels of least resistance, and instead of flowing over the trays tends to follow all possible passages at the sides of the cars, beneath the trucks or above the topmost tray. V. COST OF OPERATION Because of the fact that the University Farm evaporator during the past season was employed in the drying of numerous small experi- mental lots of grapes, our cost of operation was abnormally high. Therefore, due allowance must be made for this fact in considering our data on costs of operation given in the following summary: 1. Total tons of fresh grapes handled at evaporator 52.18 2. Total tons of dry grapes handled at evaporator 15.65 3. Labor cost per fresh ton $ 8.102 4. Labor cost per dry ton $27,015 5. Labor cost of dipping per dry ton $ 8.78 6. Labor cost of unloading trays per dry ton $10.52 7. Labor cost of general work per dry ton $ 5.69 8. Labor cost of night operator per dry ton $ .63 9. Cost of fuel per green ton (stove distillate at 8c per gallon) $ 6.23 10. Cost of fuel per dry ton (stove distillate at 8c per gallon) $21.52 11. Cost of electric light and power per green ton of grapes $ .50 12. Cost of electric light and power per dry ton of grapes $ 1.73 13. Containers for dried product (second-hand barley sacks at 8c each), cost per ton of dry grapes $ 2.00 14. Interest and depreciation at 10% (on $3500), cost per green ton.... $ 7.71 15. Interest and depreciation at 10% (on $3500), cost per dry ton $22.36 16. Total cost per green ton $28,562 17. Total cost per dry ton $74,620 18. Total cost per green ton, exclusive of depreciation $20,852 19. Total cost per dry ton, exclusive of depreciation $52,260 If the interest and depreciation are included in the cost of opera- tion the total cost per dry pound of grapes was in excess of 3y 2 c and per fresh pound over l^c. Because of our short operating season the item of interest and depreciation is excessively high. If it is omitted from the calculations the costs become approximately 2%c per dry pound and slightly over lc per fresh pound. It is certain that by conducting the University Farm evaporating plant upon a commercial basis and by adopting the modifications in methods of 442 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION operation that last season's experience have shown to be desirable, the costs given above could be very materially reduced. IV. RESULTS OF INVESTIGATIONS As many as possible of the different processes involved in the drying of grapes in the sun and in evaporators were investigated. A great deal of information was obtained, although time did not permit the completion of all the experiments undertaken nor the solution of all of the problems presented. At least one more season's work is necessary to obtain the data needed. Because of the voluminous nature of the original data, even when condensed by tabulation, it is necessary to present the results in summarized form. Investigators or others who may be interested in a detailed study of our experimental results are invited to inspect the data filed in the projects in our office. The results will be taken up as nearly as possible in the sequence in which the various evaporation processes occur. (a) DIPPING The dipping of grapes in a hot lye solution before drying has been practised for many years in the sun-drying of Sultanina (Thomp- son Seedless) grapes to hasten the rate of drying. Its use in the treatment of Muscat grapes, table grapes, and many varieties of wine grapes was thoroughly tested. It was found that different varieties exhibited a most remarkable difference in their behavior in the dipping solution. Sultanina, Tokay, Emperor, Zalbalkanski, Palomino, Black Morocco, and Cornichon gave excellent results when dipped in a boiling solution of y 2 per cent to 1 per cent lye followed by rinsing in water. The skins of these grapes were checked into numerous minute cracks extending from the stem toward the apex of the berries. Practically all berries on the bunch responded to the dipping and the checks were well distributed and uniform in size. Solutions stronger than 1 per cent lye tended to cause slipping of the skins of some of the berries. Of the grapes listed above, the Sultanina gave the best results, the berries of this variety requiring only 3 to 5 seconds' immersion in the boiling lye solution. Tokays required 10 to 15 seconds, and the checks were somewhat deeper and longer than those on the Sultanina. The same character- istics held for the other large varieties named above. Most of the wine grape varieties, such as Petite Sirah, Zinfandel, Carignane, Alicante Bouschet, St. Macaire, Mondeuse, Crabbe's Black Bulletin 322 TH e EVAPORATION OF GRAPES 443 Burgundy, Barbera, Valdepenas, Refosco, Lagrain, Gros Mansenc, Burger, Franken, and Johannesburg Riesling, Sauvignon Vert, Sau- vignon Blanc, and West's White Prolific were very difficult to check by dipping. It was necessary with these varieties to use a dipping solution of 2 to 3 per cent lye (17 to 25 pounds of granular sodium hydroxid — soda lye — per 100 gallons of water) and to maintain this solution at the boiling point. Weak solutions had no apparent effect except to remove the bloom. Many driers of wine grapes became discouraged because of the difficulty in obtaining satisfactory results and dried their grapes without dipping, thereby greatly increasing the time necessary for drying. The secrets of success lie in using a lye dip of at least 2 per cent active lye and to keep the solution actively boiling. Even under these favorable conditions, it was found that from 20 to 40 seconds' time was necessary for the grape varieties listed above. These varieties developed deeper cracks than those given in the first list above. The cracks were unevenly distributed and tended to extend at right angles to the vertical axis of the grapes rather than parallel to that axis. Many berries became softened and deeply cracked while others on the same bunch exhibited no apparent effect of the lye. The berries of some varieties tended to shatter badly from the bunches. In spite of this defect, however, the fact that dipping shortened the time of drying by one half was held sufficient reason for dipping. Muscat and Malaga grapes, because of their tough, thick skins, were the most difficult grapes of all to check by lye dipping. The berries tended to burst before the lye checked the skins. The cracks were deep and unevenly distributed. Nevertheless, dipping of these varieties is necessary for rapid drying. A 2 to 3 per cent solution of lye at 212° F. for 30 to 50 seconds was necessary for effective results. It was found practically impossible to check the skins of eastern varieties such as Concord, Isabella, etc. The effect of dipping on the appearance of the finished product is very noticeable. Dipping removes the natural bloom of the grapes and imparts a glossy appearance. Raisins from dipped grapes are more sticky than those from undipped grapes. The flavor is not materially affected unless the lye is not thoroughly removed by rinsing in clean water before drying. Where rinsing is not well done, the raisins will possess a distinct although not especially disagreeable "lye" flavor. Dipped grapes produce a raisin of sweeter taste than undipped because some of the grape acid is neutralized by the lye. 444 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION Table 1. — Effect of Dipping on Eate of Evaporation of Geapes Burger grapes, No. 2739 Tokay grapes, No. 2737 Time in hours Tempera- ture Weight of grapes undipped, grams Weight of grapes dipped, grams Time in hours Tempera- ture Weight of grapes undipped, grams Weight of grapes dipped, grams 140° F. 1500 1500 145° F. 1200 1200 4.5 140° F. 1272 1038 2 145° F. 1145 935 6 140° F. 1192 853 6 145° F. 980 515 8 140° F. 1134 728 8.5 145° F. 924 422 9 140° F. 1082 633 10 145° F. 813 317 15.5 140° F. 902 408 12.5 145° F. 728 273 17 140° F. 802 363 16.5 145° F. 630 233 19.5 145° F. 580 225 23.5 145° F. 554 227 32 145° F. 518 220 38 145° F. 378 212 40 145° F. 325 The dipping of the fresh grapes before drying is remarkable in its effect upon the rate of drying. Numerous tests upon the rate of drying of dipped and undipped grapes both in the evaporator and in the sun were made. Table 1 and the curves in figure 7 illustrate this point. The data of table 1 were obtained by drying dipped and undipped grapes on small screen-bottom trays in the laboratory evaporator at Berkeley. This evaporator is so constructed that a strong current of heated air is driven across the trays by means of a fan. Because of the high velocity of the air, the rate of drying was rapid. This small evaporator is very useful for experimental purposes because of the fact that the temperature and humidity of the air used in drying may be easily regulated. The results shown in figure 7, curve II, were obtained by weighing dipped and undipped lots of Carignane grapes during the drying of these grapes on field trays in the sun. From the table and curves it may be seen that the dipped Tokay grapes were thoroughly dried in 16y 2 hours while the undipped grapes of the same variety were not sufficiently dried after 40 hours. Dip- ping in this case more than doubled the speed of drying. Similar results were obtained with Burger grapes and several other varieties in laboratory tests. In the sun-drying tests the dipped grapes lost 65 per cent of their weight and were sufficiently dried at 20 days, while 33 days were required for the undipped grapes to reach the same degree of dryness. Dipping in this case reduced the time of drying by approximately one third. Bulletin 322 THE EVAPORATION OF GRAPES 445 In addition to the experimental results given above, measurements were made to determine the quantity of lye used in dipping different varieties of grapes. It was found that varieties such as Petite Sirah, J£oo T /Oriq E r rr< ?T cr D/ /=>/=>;/ 2& or / Z"V APORAT/ON o soo \ Yo 1 700 ' 60O V\ 1 Soo vJ <*OQ * $oo "* 6 /A 76 • AQ * #? Jb* 5? — < 77Af£- //Y 10V/Z& {°° Tf 8o\^ &L /*" rrri ~7~ C F" n/ F^f^V ft? I _d )/V ,5 ///Y niR\ '//VG 60 i. •s ^C* 5