Try cur­ing sweet pota­toes to make them even sweeter

Centre Daily Times (Sunday) - - Listings - BY BILL LA­MONT Bill La­mont is a pro­fes­sor emer­i­tus in the depart­ment of plant science at Penn State and can be reached by email at wla­m­

The other day I was at the Hor­ti­cul­ture Re­search Farm talk­ing with Corey Dil­lon and Merle Barto about har­vest­ing Dr. Luis Duque’s sweet potato re­search plots. Duque is in­ves­ti­gat­ing dif­fer­ent col­ored sweet potato clones to see if he can pro­duce small, col­ored sweet pota­toes for the spe­cialty mar­ket. That led to a dis­cus­sion about cur­ing sweet pota­toes.

Most of the com­mer­cial acreage of sweet pota­toes is lo­cated in the south­east­ern part of the United States. While at North Carolina State Univer­sity, I had the op­por­tu­nity to visit sev­eral large sweet potato grow­ers whose sweet pota­toes can prob­a­bly be found on the shelves of our stores in State Col­lege.

The sweet potato, Ipo­moea batatas, is a ten­der, warm-weather veg­etable that re­quires a long frost­free grow­ing sea­son to ma­ture large, use­ful roots. That is why in the North­east we rec­om­mend us­ing black plas­tic mulch and drip ir­ri­ga­tion to grow sweet pota­toes in the gar­dens and is the sys­tem that Duque used at the Hor­ti­cul­ture Re­search Farm. Sweet potato is na­tive to Cen­tral and South Amer­ica and is also a rich source of vi­ta­min A.

Though or­ange-fleshed va­ri­eties are most com­mon to­day, white or very light yel­low-fleshed types were once con­sid­ered the finest types for so­phis­ti­cated peo­ple. Some white-fleshed types are still avail­able, though they may be hard to find out­side the Deep South.

The sweet potato is not re­lated to the yam, though in the mar­ket­place the two names are of­ten used in­ter­change­ably. The true yam, Dioscorea sp., is an en­tirely sep­a­rate species that grows only in the trop­ics. This sit­u­a­tion is sim­i­lar to the use of the terms muskmelon and can­taloupe. We only grow muskmel­ons in our gar­dens.

Sweet pota­toes are warm-sea­son plants that are very sen­si­tive to cold tem­per­a­tures. The tuber­ous roots should be har­vested by the time frost kills the vines or soon there­after. Sweet potato roots con­tinue to grow un­til frost kills the vines. Roots can be left in the ground for a short while; how­ever, an ex­tremely hard frost can cause dam­age to roots near the sur­face. Chill­ing in­jury also re­sults to roots when soil tem­per­a­tures drop to 50 de­grees or lower, and this can re­sult in in­ter­nal de­cay in stor­age. The great­est dan­ger from de­layed dig­ging is the risk of cold, wet soil en­cour­ag­ing de­cay of the roots.

De­pend­ing on how early you were able to plant, you may find an as­sort­ment of “baby baker” or smaller roots, as well as full-size pota­toes. Although you can cook newly dug sweet pota­toes right away, their fla­vor and stor­age qual­ity is greatly im­proved by cur­ing at warm tem­per­a­tures first. It is dur­ing the cur­ing process that starch is con­verted to sugar.

Care should be taken dur­ing dig­ging and han­dling to avoid skin­ning and bruis­ing the roots. Even a small wound can eas­ily be­come in­fected with de­cay or­gan­isms. Line con­tain­ers with rags or other soft ma­te­rial, if pos­si­ble, to avoid scratch­ing the roots. Do not store badly in­jured or dis­eased roots. You do not want large amounts of soil cling­ing to roots dur­ing stor­age but be care­ful in removing the soil as sweet pota­toes are eas­ily dam­aged dur­ing the wash­ing process when freshly dug. It is rec­om­mended to al­low roots to dry and cure be­fore removing ex­cess soil.

Sweet pota­toes can be cured by hold­ing them for about 10 days at 80-85 de­grees and high rel­a­tive hu­mid­ity (85-90 per­cent). In the ab­sence of bet­ter fa­cil­i­ties, they can be cured near a fur­nace to pro­vide warmth. If the tem­per­a­ture near your fur­nace is be­tween 65-75 de­grees, the cur­ing pe­riod should last two to three weeks. To main­tain the re­quired high hu­mid­ity (85-90 per­cent rel­a­tive hu­mid­ity), stack stor­age crates or boxes and cover them with pa­per or heavy cloth. Pack­ing in per­fo­rated plas­tic bags will also keep hu­mid­ity high, yet the per­fo­ra­tions will al­low ex­cess mois­ture to es­cape.

Once the sweet pota­toes are cured, move them to a dark lo­ca­tion where a tem­per­a­ture of about 55-60 de­grees can be main­tained dur­ing stor­age. Sweet pota­toes are sub­ject to chill­ing in­jury, so keep them out of the re­frig­er­a­tor. Wrap­ping cured sweet pota­toes in news­pa­per and stor­ing them in a cool closet can ob­tain good re­sults. Then sit back and en­joy the great nutri­tional value of sweet pota­toes and also some ex­cel­lent sweet potato pies. I am look­ing for­ward to the re­sults of Duque’s re­search.

CHRIS WALKER Chicago Tri­bune via AP, file

Sweet pota­toes are warm-sea­son plants that are sen­si­tive to cold tem­per­a­tures.

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