BU NO. I 2 NOVEMBER, 1923 Harvesting and Storing Sweet Potatoes By J. C. C. PRICE AGRICULTURAL EXPERIMENT STATION of..the ALABAMA POLYTECHNIC INSTITUTE DAN T. GRAY, Director AUBURN SUMMARY These experiments indicate rather definitely that: 1. The splendid keeping results reported in Bulletin No. 197 were due quite largely to the fact that potatoes were dug before vines were frosted and then stored and cured properly in a house. 2. Regardless of curing methods potatoes dug after vines are damaged by frost will not keep as well as they would if dug before vines are frosted. 3. The old belief, common among farmers, that "it is safe to delay harvesting until frost has killed the vines" is not only unsafe but will result absolutely in loss of potatoes even though harvesting is done immediately after vines are frosted. 4. Banked potatoes get pithy and lose their food value quicker than house stored potatoes. 5. The ultimate loss in eating, keeping, and germinating is increased in proportion as harvesting is delayed after vines are frosted. 6. Vines may be removed a few days before harvesting without causing loss to either eating or keeping qualities. 7. Lack of curing may cause discoloration without spoiling the product for food. 8. Properly harvested and well cured sweet potatoes will stand a lower temperature without damage than uncured potatoes. 9. Properly grown and cured potatoes do not require much ventilation when stored in houses. 10. Comparative weight loss of house stored potatoes over bank stored potatoes is not as great as is usually thought. 11. If potatoes are dug and placed in a storage house during curing it is better to fill each bin gradually rather than completely at one time. This will prevent over-curing near the ceiling. 12. Further investigation should be made to determine the chemical changes that take place in potatoes under different growing, harvesting, and storage methods with a view to improving present methods of handling this important crop. HARVESTING AND STORING SWEET POTAOES By J. C. C. PRICE* Previous to the fall 1917 it had been revealed by the Alabama Experiment Station that it is more economical to store sweet potatoes in houses than in pits, banks, or trenches, and that it is easier, cheaper, and less risky to market sweet potatoes from curing houses than from banks, pits, or trenches. These facts have been reported in Bulletin No. 197 of the Alabama Experiment Station. During 1917 potatoes were grown to continue certain phases of work reported in Bulletin No. 197. On October 24th an unexpected frost killed practically all of the potato vines. The writer had evidence from previous work and observations, that potatoes from frosted vines would not keep well and were not satisfactory for human food. However, storage tests, as reported in Bulletin No. 197, were carried out with pototatoes dug before vines were frozen which made it necessary to get, as nearly as possible, potatoes that were not damaged by the freeze. So, vines were removed with a hay rake on the morning of October 25th. The crop was harvested October 30th to November 2nd and cured for five days in a curing house. At the end of the curing period, the temperature was running low on the outside of the house and it was closed tight. Examination on November 2nd showed rots and molds appearing on cut surfaces. For several days the ventilators were opened during the day and closed at night. This, apparently, stopped the molds. Toward the end of the month much rain fell and moisture collected on the inner walls of the storage house, causing it to appear as if sweating. Fires were built four times during December to correct this condition. During three days, from December 14th to 17th, inclusive, the temperature in the house went to and remained at 40 degrees F. In January potatoes continued to sweat and upon examination were found to contain black streaks and pithiness, and when baked many of them were unfit for food. About fifty percent was sound enough to be used for seed. *Now at Mississippi Agricultural and Mechanical College. 4 This very heavy loss and the storage behavior of the potatoes seemed to be so very important and so different from the common belief among farmers that "it is not necessary to dig potatoes until the morning following the first killing frost," .that it seemed advisable to begin investigations immediately to determine the cause of such behaviour and suggest methods of avoiding such losses. The writer started tests in 1918 to determine whether or not this loss wascaused from frosted. vines, and if: so, whether or not such losses could be prevented, (1) by digging immediately after vines were frosted;, (2).by removing vines as quickly as they were damaged by cold; (3) or by removing vines before digging. Investigation was made also to determine whether or not insufficient curing or low storage temperature could have caused the loss. It was convenient to conduct.tests along with these-experiments to secure some preliminary information on, (1) the effects of ventilation during storage periods on house cured potaoes; (2) loss by weight of house stored and banked potatoes; (3) variation of temperature at different elevations in storage houses during curing; (4) and general humidity and temperature behavior in banks ,and houses during curing and storage. COMPARISON OF KEEPING AND EATING QUALITIES OF Po- TATOES DUG BEFORE AND AFTER. VINES WERE FROSTED To test the effect of frosted vines on the keeping and eating qualities of sweet potatoes, Triumph and Porto Rico varieties were planted at the same time, in the same field, in similar soils, and grown under similar cultural conditions. This assured uniformity of product. For this test, one lot of potatoes was dug, before frost and cured in storage house. A second lot was dug before frost and banked in the regular way with pine straw. Five to ten days after the vines were frosted a third lot was dug and placed in the storage house and a fourth lot was dug and placed in banks. The third and fourth lots were treated as nearly like the first and second lots as possiblei: .. This treatment was' as.. follows: Potatoes in" storage carried through a curing process ten to twelve days 'at a temperature varying from 80 to 90 degrees F, as outlined in were Bulletin No. 197, then lowered to a temperature of 50 to 60 degrees F, and kept as near this temperature as possible. Preparatory to banking, potatoes were carefully sorted and piled on a thick layer of pine straw, covcred carefully each night to keep off dew and prevent chilling, and uncovered each (ay to allow drying by the sun. This was (one for three (ays, and the potatoes were then covered with a layer of pine straw 6 inches thick and 8 inches of soil as shown in Figure 1. ,- ~ ".:-"~: PC I. ,,pp -~ ~--* i ---:~ I '"'""~-. ; Ct~i f.I .. ? ~~ ;~;li -r, ~-~~: .*r .-- --1' -" , ;; - Fja. I.-Showin{1 How Potatoes Were Banked A hole five inches in diameter was left in the top of the bank for ventilation. Pine straw was stuffed into the ventilator in the top of the bank during low temp'erature periods. A wooden box about 2 feet square was turned over the top to keep out rain. It was removel on warm, sunny (lays if the top of the bank had the appearance of sweating. Bank was not disturLed throughout the storage period. A thermograph Nvis used for recording the temperature in the bank. :RESULTS OF STORAGE TESTS The following notes were taken on different lots of potatoes in storage: Lot 1.-Triumph, 100 bushels, dug before frost and stored in bank November 15, 1918. Examined March 18, following. Loss 5%. Lot 2.-Triumph, 10 bushels, dug before frost and stored in bank November 15, 1918. Examined March 18, following. Loss 5%. -Lot 3.-Triumph, 10 bushels, dug 10 days after frost and banked December 13, 1918. Examined March 18, following. Loss 85%. Lot 4.-Triumph, 1 bushel, dug 10 days after frost and stored in house but not cured, December 13, 1918. Examined March 22, following. Loss 96%. Lot 5.-Porto Rico, 50 bushels, dug before frost and stored in house November 7, 1918. Examined April 15, following. Loss .8%. Lot 6.-Porto Rico, 10 bushels, dug before frost and banked November 15, 1918. Examined March 18, following. Loss .62% Lot 7.-Porto Rico, 10 bushels, dug 10 days after frost and banked December 13, 1918. Examined March 18, following. Loss 50%. Lot 8.-Porto Rico, 1 bushel, dug after frost and stored in house but not cured. Examined March 22, following. Loss 75%. Lot 9.-Triumph, 100 bushels, dug before frost and stored in house November 5, 1919. Examined April 12, following. Loss .4%. Lot 10 -Triumph, 10 bushels, dug before frost and stored in bank November 5, 1919. Examined April 7, following. Loss .7%. Lot 11.-Triumph, 5 bushels, dug 5 days after frost and banked December 19, 1919. Examined April 7, following. Loss 80%. Lot 12.-Triumph, 4 bushels, dug 5 days after frost and stored in house December 19, 1919. Examined April 12, following. Loss 75%. Lot 13.-Porto Rico, 100 bushels, dug before frost and stored in house November 5, 1919. Examined April 12, following. Loss .8%. Lot 14.-Porto Rico, 10 bushels, dug before frost and banked November 5, 1919. Examined April 7, following. Loss 1.25%. Lot 15.-Porto Rico, 5 bushels, dug 5 days after frost and banked December 19, 1919. Examined April 7, following. Loss 75%. Lot 16.-Porto Rico, 6 bushels, dug 5 days after frost and stored in house December 19, 1919. Examined April 12, following. Loss 71%. In addition to the above examination, potatoes that were dug before and after frost were taken from banks and house and baked with the following observations: Triumphs dug before frost were in excellent condition, had no discoloration, were sweet, soft, uniform in texture, stringless, excellent in quality, good color, and free from lumps. Triumlphs dug five days after frost had killed the vines, showed discoloration and pithiness when cut. When baked they were lumpy, slightly stringy, and poor in quality. They showed (ark streaks throughout. had a bad taste and olor, andl were unfit for food. i'i.. 2.-Potato I)namged by Freezing. Note the Blackening of the Cambium from which Peeling Separates. Porto Ricos dug before frost kept in good condition. When baked they were soft, sweet, juicy, tender, uniform in texture, and good in color, flavor, and quality. Porto Ricos lug five (ays after frost had killed vines showed (liscoloration andl pithiness when cut. When b~aked they shole air spaces and were stringy, lumpy, wet, poor in texture andl flav or, and showed discoloraThey were unfit for food. tion throughout. Both varieties (lug before frost appeared healthy and, when bedlledl, Iroutlced good sprouts in due time while those (ug after frost andl cured in house appeared dlead and d(il not loduce good sprouts. Those (ug after frost andi storecl in b~ank had a tendency to sprout before the regular season. What might be termed a second growth took place, making the potatoes unnarketallc. This was due to heating caused by the rapid decay of a large portion of the total lot as shon by notes on page 6. INFLUENCE OF TIE OF HARVESTING ON KEEPING ANI) EATING QUTALITIES OF POTATOES FROM FROSIED VINES To make this test potatoes were dug the day the vines were frosted and five andl ten (ays alter frost. Potatoes dug the (ay the vines were frosted lost 11', in banks and 10 percent in storage house. Some showed a trace of pithiness and were counted as loss, but whell baked they had a good flavor and color. Potatoes (ug five days after frost lost 50 to 85 percent by rot and the remainder that appeared sound were not fit for food when baked. These results are similar to those of 1917. Potatoes dug ten days after vines and foliage were frosted were a total loss. This is shown in Figure 3. i I It" Fic 3.-Triumph Potatoes Dug 10 Days After Frost, 1918, and Stored in Bank; 85% Rotten and Remainder Worthless. Potatoes dlug eight (lays after 50 percent of foliage was killed alpeared to be in good condition, but when cut they Iweir' found to be pithy andi woody and contained black streaks. The loss in this lot by rot was 2 percent in house and (1j percent in bank. When baked1 these potatoes showed discoloration, air spaces, h l nnattracti\ c8C5,ss, al had poor t'laor and color. EFFECT OF CUTTING VINES BEFORE DIGGING Vines were removed from two lots October 22, 1919, and ends of the stems of potatoes were covered with soil to protect them from frost. One lot was dug fifteen days after vines were removed and the other lot thirty days after. There was no loss from potatoes lug before frost. Two crates of 50 pounds each were selected from each digging, cured and stored in storage house, and some of the thirty day lot was banked without curing when dug. Those in the house were examined May 16th. Two potatoes of the fifteen-day period had rotten ends and showed traces of pithiness while the remainder, and the two thirty-day lots, were sound and in excellent condition. When baked these potatoes were free from lumps, stringiness, or discoloration. They were sweet, fairly juicy, and of excellent flavor and texture. The lot in banks was examined April 12th. A bushel contained one rotten and five with rotten ends, with 50 percent pithy. When baked, they had good flavor and color, but showed pithy streaks. The pithiness was evidently due to being placed in storage in an uncured condition as shown elsewhere. FIG. '.ctft (ros Secoon from 'Those )ug Before Frost; on Right . -On Cross Section from Those Du- After Frost. 10 A lot of two hampers was dug before frost, cured in a storage house and removed to storage cellar or storage pit. A second lot was dug and placed in cement cellar immediately after digging. When examined in April the cured potatoes showed no discoloration or pithiness, while the uncured potatoes showed dark streaks and were pithy. When baked all were sweet, juicy, and of good flavor and texture. EFFECT OF Low TEMPERATURE WHILE IN STORAGE ON KEEPING QUALITIES To determine whether or not low storage tempera1917 ' could have caused heavy loss a number of ture of: experiments were conducted to find the lowest temperature potatoes dug before frost and properly cured would stand without injury or loss by decay. Lots of 20 selected cured potatoes were placed in the weather shelter by a thermograph machine and the following observations made: January 2nd.-Potatoes subjected to temperature of 36 degrees Fahr., and remained below 40 degrees Fahr. for ten hours. Examined May 5, following, and found in excellent shape, sound, juicy, and of good quality. January 3rd.-Potatoes subjected to temperature of 32 degrees Fahr., and remained below 35 degrees Fahr. for 8 hours. Examined May 5, following, and found in excellent condition, sound, juicy, and of good quality. January 5th.-Potatoes subjected to temperature of degrees Fahr., and remained below 32 degrees 29 Fahr. for 6 hours. Examined May 5, following, and showed slight injury at cambium, but otherwise in good condition. March 6th.-Lot subjected to 24 degrees Fahr. for 6 hours, and remained below 32 degrees Fahr. for 15 hours. Examined 25 days later. Seventy percent were rotten and the remainder in bad condition. March 7th. -Lot subjected to 23 degrees Fahr. for 5 hours, remained below 32 degrees Fahr. for 12 hours, and night of 8th subjected to 20 degrees Fahr. for 1 hour and below 32 degrees Fahr. for 13 hours. All rotten 2 days later. March 9th.-Lot subjected to temperature of 27 degrees Fahr. and returned to storage house in 24 hours below 32 degrees Fahr. for 9 hours. May 5th showed a slight leatheriness and discoloration when cut. All were sound. I I0\\e\ er surly risks should1( o lt Itoil\ioii I iniju[ri. )110 elo dtiegrees Falir. t lj a Ii I 11)1 he taken. .. \ lu)isid in all of Triiiiiijiis wer is not I'eollllllelidtc. Iiin lIn ofitoe oi'der' toi deterin~e thle %14 intltieii ot little orP no 14n1d dug b\oX 11 l flSiiI.r(I)I'iii P W S. cued~'i, Ill (\ rX \ aX. T his inica~tes that JIitlIhis diL be(1ore' iiith storaige 1et((. \ islll iugL ere seof 50t p~oundls each we ighed at regulri initervals dutrstorage jierioul. T-wo hackcadi and a11( the nuC pei(Vi andI cipriuiteIt iln thin 19t1-1 XXe (lUr discardi144 .i ~Ithii.s andii '~ 1, V r. -1 a' X S. n' p Fn4. 5.- tIriulllfh t'otlitiwns 1)u- Becforec Vines Stored in 13ak: 99.31, Sound. -were F~rosted, 1919, and 1:2 one potatoes in the package in 1919-20 The TABLE I. because of decayed potatoes. other 7 packages kept without loss in quality or color. In the experiment a No. 1 grade of potatoes was used. Losses in weight during the curing period and at the end of the storage period varied very little. Loss IN WEIGHT OF POTATOES STORED IN HOUSE 1918-1919 Date Nov. 8 9 --= _ _ _. Lot 1* Lbs. 10 50 49 .5 0 11 -------12 ________ 13 14 -- _-___ 15.. _____e__ Lot 2* Lbs. 50 Lot .4 Lbs. 3* 49.27 49 .4 8 49.25 48.80 50.9.4 6 49.22 48.82 16 17 18 -------- -47.85 48.86 48.67 48.35 48.10 . 47.93 47.60 47.40 48.65 48.32 48.05 47.86 47.80 47.65;47.55 48.65 48.3,4 48.10 47.88 47.82 March 22-19 44.55 *Triumph potatoes used. Averaige loss 10.7%. TABLE - 47.55 44.90 47.35 44.50 - II.-LOSS IN..XWEIGHT OF POTATOES STORED IN HOUSE, 1919-20Q.. Date Nov. 6 -.. _ _ 7 8 10 11 _ 12 ------ Lot 1* Lbs. 50 49.35 -48.65 )Lot,2* Lbs. 50 49.65 49.00 48.10 48.05 47.95 47.55 47.50 46.50 43.55' Lot ** Lbs. 50- Lot 4* Lbs. 50 49.65 49.70 47.35: 47.10 46.95 49.00 48,4a 48.20 47.45 46.35 43.80 48.80 48.00 47.85 47.45 May, 16-20 .- 43.20 Average loss 12.97%. - 14 15 27 _ 46.50 46.30 45.50 48.10. 47.50 46.90 46.65 45..40 43.50 *Triumph variety used. * *Porto Rico variety used. WEIGHT Loss IN BANKS One lot of potatoes was selected, nuniibered, weighed, and placed in a storage bank, November ,15, 1918, another .lot was handled in the same way, and stored in bank November 5, 1919'. The first lot remained in bank- until March 18, 1919, and lost 4.15 percent of its weight. a ,and 12, 1920, and, lost' 6.91 percent of its weight. In each case the .bank remained closed- until .the potatoes [were taken out and weighed. These lusses are compared in Table III which The, second lot remained in bank until April follows. l \I. ill. \\ ]A) .i Ii LWSN IN MlOUSE AND) IN B3ANK I)itt Storage Began Nov. 8, 1918 Nov. 15, 1918 Nov. 15, 1918 Nov . 5, 1919 Eanded Date Storagc March 22, 1919 'May 16, 1920 March iS, 1919 Storage \lu thod [louse I luose Percent Loss 10.7 12.97 -1.15 1.91 Ilaak 1Kaoil April 12, 1920 be Iubs~rv((i [IhaL the a ela(gc storag~e peaverage \\~i fu r ti' han it i Daki . 'I( Ioss o)1 1hs( siN tored inl hious5 \\ as 11.83 perceent mid the 5.53 percent. ax ei& loss it bank~s Nvi ii' It shouti( t ii ous \A. 1918. mit Stoied in Bank: 5',' Loss. 't'able IV, helm\\. shiow~s therret erflIread~inlgs at top o)1 b~in, at floor', an1( tihlt' av between. Biefore a fire During the curNvas built iil i'e:Idhitgs xx tw the sane. in" seasonl thtem were variatioits of 7 to 29 dlegrees 1:4 TABLE I.V.-TEMPERATURE OF ROOM DURING CUBING Date; 1918 Time Temp, at Temp. midway top of bin between floor at floor and ceiling Degrees F. Temp. Degrees F. Degrees F. Nov. 5 7:00A.M. 9:00 A. M. 2:30 P..M. 4:00 P. M. 7:00 9:00 12:00 3:30 4:30 7:00 9:00 2:00 5:00 A. A. M. P. P. A. A. P. P. M. M. M. M. M. 58 94 78 90 63 74 81 84 84 67 90 80 88 . 67 86 86 73 90 58 82 78 58 71 71 86 60 71 Nov. 6 56 58 65 66 .68 71 72 73 64 52 61 67 63 54 70 60 70 72 Nov. 7 ____ M. M. M. 63 73 73 77 63 75 Nov. 8 7:00 A. M. 1:30 P. M. 5:00 P. M. 75 81 64 Nov. 9 10:40 7:00 A. A. 3:30 P. 5:00 P., M. M. 67 82 84 69 M. M. 90 90 73 68 70 63 Nov. 10-.-- 7:00 A. M. 4:30P.82 75 64 69 54 Nov.. 1 1 7:00-A. M. 9:00 A. M. 2:00 P. M. 90 82 81 5:00 P. M. Nov.: 127:00 A. M. 8:30 A. M. 2:00 P. M. 80 70 88 74 68 74, 72 64 76 68 59 72 68 60 54 58 63 44 Nov. 13 7:00 - A. M. 8:30 A. M. 6:30 P. M. Nov. , 14 7:00 9:00 3:00 7:00 A. M. A. M. P. M. P. M. 80 78 74 86 83 76 76 76 71 69 70 70 75 70 58 58 . 58 60 68 .,62 62 68 Nov.- 15 9:00 A. M. 5:00 P. M. 74' 7272.6 Average 76.9 62.8