Proceedings of the 7 th International Working Conference on Stored-product Proiectuni - Volume 2

Popcorn conditioning and pest control

DIrk E. Maier! , Darren J. Zink", Michael D. Montross", Lmda J. Mason2 and R. David Cromptorr'

Abstract

The Purdue Post-Harvest Aeration & Storage SimulationTool (PHAST) was used to evaluate several temperature andmoisture management strategies for two commercial popcornfacility sites m the U. S. Energy consumption, average drymatter loss, moisture shnnk, moisture umforrmty andinsect development were weighted to determme theoptimum drying/conditioning and non-chemical storagemanagement strategies for three harvest dates. For theEastern Corn Belt location, fan control for drying based on afixed equilibrium moisture content (EMC) wmdow followedby an adaptive EMC-based strategy With an uppertemperature limit of 15.6"C durmg storage was identified asthe best strategy for all harvest dates. For the CentralPlains location, an EMC window-based conditioning strategyfollowed by chilled aeration during storage were found to bemost effective for the three harvest dates.

Introduction

Popcorn IS an Important cash commodity for midwesternfarmers which has nearly tripled m production between 1970and 1994 (Popcorn Institute, 1995). Historically, Indianaranks as the largest popcorn producmg state in the nation.In 1995, Indiana produced approximately 23% of thenation's crop generatmg approximately 27 million dollars ofon- farm income (Gann, 1996).Popcorn has to be preserved carefully to maintain the

popping volume of the product. Research has proven thatthe poppmg volume is directly related to kernel moisture(Willier and Brunson, 1927; Hanes, 1973; Haugh et al ,1975; White et aI. , 1981). The key for popcorn quality isconditionmg. Typically, popcorn processors will overdry thepopcorn during the fall drying season, requmng them toattempt to rewet the gram in the spring. ThIS not onlymcreases the operational costs but generally raises thetemperatures in the bin for optimum insect development.

1 Department of Agricultural and Biological Engmeenng

2 Department of Entomology, Purdue Unrversity, West Lafayette,Indiana, 47907-1146, USA

3 OPIsystems, 1216- 36 Avenue NE, Calgary, Alberta, TIE 6M8,Canada

Maintammg quality becomes a major concern duringstorage Temperature management is one defense that canbe used while grain is in storage because msects aresensitive to temperature changes in their environment(Mullen and Arbogast, 1984). Storage temperatures canmfluence insect population growth by reducing rates ofdevelopment and survivorship (Hagstrum and Throne,1989).

Objective

The goal of this research IS to optimize popcorn quality bydetermming optimum site-specific management strategiesfor popcorn stored in corrugated steel bins durmg good,normal and poor storage years in two U. S. locations(Northeastern Indiana-Fort Wayne; Western Kansas-DodgeCIty) that will maintam or improve the desired qualityparameters achieved durmg fall conditioning whileminimizing dry matter loss (DML) and insect infestationduring the remamder of the storage season (up to twelvemonths).

Literature Review

The objective of storage is the mamtenance of physical andnutritive grain properties. Bailey (1992) mdicated thatdeterioration of grain begms at harvest and the rate ofquality loss depends upon storage conditions. Physical andchemical-based techniques are the primary pest controlmethods for stored gram. Usage of chemical-based methods(1. e., fumigants, residual insecticides and non-chemicalgrain protectants) has progressively been restricted duringthe past ten years. Currently, only two grain fumigants,phosphme and methyl bromide, remain in CIrculation.Methyl bromide has been classified as a significant ozonedepletmg substance by the 1994 Science Assessment ofOzone Depletion (Thomas, 1997). Under the Clean Air Actof 1990, the Environmental Protection Agency (EPA) hasprohibited the production and Importation of methyl bromidestartmg January 1, 2001; and has frozen U. S. productionand Importation to 1991 levels (Thomas, 1997). Inaddition, protectants, such as organophosphates andpyrethroids, are under pressure from both domestic andinternational gram consumers due to chemical residues ingram as well as development of resistance by target pests.Chilled aeration is the process of lowering the grain

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Proceedina« of the 7th Iniernatumal Worhng Conference on Stored-product Protection. - Volume 2

temperature for the control of insect and fungal developmentindependent of ambient conditions. The goal of chillmg is topreserve gram quality For the past 35 years, thistechnology has been successfully utilized in over 50countnes having an annual chillmg capacity of over 20rrulhon metnc tonnes of gram (Maler et aI., 1993). Sincestored-gram insect pests function over a narrow temperaturerange, chilled aeranon IS an effective alternative forcontrollmg stored-product insects Maler et al ( 1996 )demonstrated using a simulation model the effect of storagemanagement practices for a range of weather conditionsFall chilled aeration was the most effective strategy for allcases studied With the model. Spnng ambient aerationcaused an increase in DML while summer rechillmgImproved insect control WIthout increasing DML. Controlledfall ambient aeration in conjunction WIth summer chilledaeration has excellent potential m preventing stored-productpests WIthout the use of residual pesticides or fumigantsRulon (1996) investigated the annual operational costs

and amortized net present costs of chilled aeration versusambient aeration and furmgation treatment for U. S.conditions, It was determmed that the annual operatmgcosts of the chiller were 22 - 56 % low'er than for thetradltlonal treatments In addItIon, several case studIes onpopcorn and wheat establIshed the commercIal feaslblhty ofchIlled aeration Thus, despIte the mitial capItalmvestment, chIllmg was economIcally JustifIed commerCIallywhen the vanable costs were ffilmmlzed over tlme.Adams (1994) SImulated eIght common management

practlces for three dlstmctive chmate locations to illustratethe mfluences of region and weather on the control of DMLand maIze weeVIl populations. Of the eIght strategies, non-aerated storage proved to be the most meffectlve andundeSIrable, whIle fall-chIlled aeratlon was found to have themost effect regardless of locatIon or weather situatlon. Thestudy showed that a combmatlon of controlled ambIentaeratIOn m cOUjunctlon WIth chilled aeratlon had SIgnifIcantpotentIal as a non-chemIcal and preventatlve pestmanagement techmque for most locatlons and weathercondltlons

Procedure

Using the PHAST simulatlon program (Maler, 1992 ;Adams, 1994; Montross, 1997), the two locatlons selectedfor the storage model were Dodge CIty, Kansas and FortWayne, IndIana. Each represents a different type of chmatem whIch popcorn IS grown and harvested Dodge CIty,located m the Central Plams, has hIgh temperatures duringmuch of the year and low relatIve humIdItIes year-round;whtle Fort Wayne, located m the Eastern Corn Belt, hasmoderate temperatures and Widely fluctuatmg relatIvehUffilditles (Ruffner, 1985).

Four storage strategies were modeled withm PHAST:

Non-aerated storage, Sentry PAC® aeration, Seed wet-bulbtemperature aeration (SWBT) and Chilled aeration. Thenon-aerated storage strategy provides a worst case scenanoto determine maximum insect populations and DML during astorage penod. The commercially available controller(Sentry Technologies, 1993) allows the operator to setadaptive parameter bands that are favorable for fan operationaround a desired target temperature and fmal moisturecontent. Aeration based upon SWBT IS a strategy designedfor warm and dry climates as a means of controlling insectpopulation growth (Wilson and Desmarcheher, 1994).SWBT IS defined as the wet-bulb temperature of the arr inmoisture equilibrium WIth the seed. It is calculated from theknown moisture equilibrium properties for the seed type,the dry bulb temperature and moisture content of the gram.Aeration occurs whenever ambient conditions are below theselected SWBT temperature. Chilled aeration uses a mobilerefrigeration unit that cools air across the cooling coil, thenreheats the atr across a secondary condenser until theequilibrium relative humidity of the bm inlet arr IS inequilibnum WIth the target gram moisture content. TheEMC equation of Flood and White (1984) IS used in thepopcorn storage model.The standard mput parameters for the PHAST slffiulatIons

are summanzed m Table 1. For the Sentry PAC strategy,target mOisture content set points of 14.5, 15.5, 16.5,17.5 and 18.5% w. b were evaluated m combination WIthmaximum temperature lImIts of 15.6, 20, 30, 40 and 50t: .For the SWBT strategy, temperatures of 9, 11, 13 and15°C were evaluated m combmatlon WIth a maXImum EMCset pomt of 14 5% The mputs for the chIlled aeratlonstrategy are summanzed m Table 2. The PHAST simulationoutputs five cntIcal vanables that are used to determme thebest SIte-speCIfic storage strategy These vanables are:shrink loss from the target mOisture content (1. e. , 14.5%w b.), nonumformlty of the popcorn mass outSIde of anacceptable mOisture content range (1. e. , 13 - 16% w. b. ),average bulk DML, total maIze weevtl populatIon, and kWhof energy used per bushel. These vanables were selectedbecause of theIr Importance to the end user. Ideally, a userwould want these variables to be as low as possible for anygIven strategy. ThIS would reduce energy expenses andproduct loss due to moisture shrink, msect mfestation andgram spOilage. The selectlon of representative good,normal, and poor storage years (as proposed by Stroshme,et al. , 1992) for the SImulatIon of theses strategies at thosetwo locatIOns IS described m detaIl by Zmk (1998)

Results and Discussion

Conditioning

For each locatlon, drymg began on a designated harvest

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Proceedinas of the 7th International Working Conference on Stored-product Protection - Volume 2

date. The procedure and results for the selection of theoptimum site-specific conditioning strategies were previouslypresented (link et al , 1997). The selected strategies forDodge CIty were contmuous natural arr WIth target andmaximum moisture Imuts of 14.5%/15.0% (September1), EMC-wmdow of 12 - 23% with moisture linuts of15.5%/16.5% (September 15) and EMC-wmdow of 12-25% With moisture lmuts of 15.5%/16.5% (October 1);for Fort Wayne the selected strategies were EMC-window of12 - 24 % (October 1), EMC-Window of 10 - 23 % (October15) and EMC-window of 10 - 24% (November 1) all withtarget and maximum moisture hmits of 14.5% and 15.5%,respectively. The simulation of the storage strategies isuutiated after completion of the selected conditionmgstrategies for each harvest date and location. The mputvalues to the storage strategies are the endmg values fromthe conditionmg strategies. DML IS calculated on anaccumulated baSIS over 12 months from the beginning of thedrying season Shnnk loss for the storage strategy selectionIS measured as the difference between the conditionmg andstorage average bm moistures. It IS represented as anegative value when additional moisture IS lost duringstorage, and as a positive number when the storage strategyadds moisture to the gram mass. No cost functions wereassigned to each critical variable. Thus, rankmg ofstrategies was based on mirnrmzing the critical variables.

Table 1. Summary of standard mput parameters for theweather data analysis, drying and storagestrategies using the PHAST code.

Parameter Value

Bin Height (m)Bm Diameter (rn)Total TonnesInitial Grain Harvest Temperature caC)SeptemberOctober and NovemberInitial Moisture Content (%w. b)Initial Dry Matter Loss (%)MOisture Uniformity RangeBulk Density (kg/m)Initial Maize Weevil Immatures ( # /bu)Initial Maize Weevil Adult Males (# zbu)Initial Preoviposition Females ( # /bu)Initial Adult Female Maize Weevil (# /bu)Remfestation Rate ( # /day)Number of Gram LayersNumber of Grain ColumnsDrying Time Step (h)Storage TIme Step (h)Barometric Pressure (rnb)Fan Power (kW)Fan Efficiency (%)Apparent Air Velocity (rn/s)Pre- Warmmg of Plenum Air due to Fan cc )

6.77.3195

211220o

14-15720o1o11214711

10137.55010011.1

Table 2. Summary of mputs for the chilled aeration storagestrategy.

SetpomtFort Wayne, Dodge City,

IN KS

Desired Grain Temperature 15 14

caC)

Allowable Grain 3 3Tempera ture Increase (OC)

Evaporator Air Temperature 8 4

caC)

Reheater Air Temperature 13 12

caC)

Duct Heatmg (OC) 1 1

Design Airflow Rate ( rrr' 0.1 0.1mm - 1 tonne - 1)

Pest control

A complete rankmg analysis of the storage strategies forboth Dodge CIty and Fort Wayne was compiled and discussedby Zmk (1998) and link et al. ( 1998). The total number ofstorage simulations were 24 for Dodge City and Fort Wayne,respectively. Several storage SImulations had duplicate

results. For example, the Sentry PAC® strategySImulations for any target moisture setpoint and maximumtemperature limits of 50°C, 40'C, and 30°C had the sameresults regardless of location. Thus, only the temperaturelimit of 30'C was used m the ranking analysis Likewise, inDodge CIty the SWBT strategy With the 15'C temperaturesetpoint and no EMC limit had identical results for thecritical variables as the SWBT temperature of 13°C. Thus,this strategy was also removed from the ranking analysis.Storage strategies that did not use aeration were alsoremoved from the rankmg because these strategies createdunacceptably high msect populations, and are consideredunrealistic for quality gram managers. Storage strategiesthat exceeded the 0.5% DML Iinut were not removed fromthe rankmgs because of the length of the storage penodmvolved, which would allow for earlier unloading of bms If

needed

Dodge city

For the September 1 harvest date, only four storagestrategies appeared in all three weather years. These

strategies were Sentry PAC® aeration with a targetmoisture of 18.5 % and a temperature limit of 20°C, chilledaeration, and SWBT aeration with temperatures of 1rC and13°C and a maximum EMC limit of 14.5%. When ranked

across years, the Sentry PAC® and chilled aeration

strategies were the best with the Sentry PAC® one slightly

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Proceeunqs of the 7th Internatwnal Worki'tl{]Conference on Stored-product Protection - Volume 2

ahead For the September 15 harvest date, eight storagestrategies appeared in each of the weather years. A majority

of them were either Sentry PAC® or SWBT aerationstrategies. When ranked across years, chilled aeration was

first while Sentry PAC® strategy ranked second, third,sixth and eighth. The SWBT aeration strategy rankedfourth, fifth and seventh For the October 1 harvest date,

the Sentry PAC® aeration strategy dommated the top tenpositions in each weather year. Out of seven matching

strategies, there were five Sentry PAC® strategies and oneeach chilled and SWBT aeration The top two strategieswere very close in the overall rank across the weather

years The Sentry PAC® mode with an 18.5 % targetmoisture and a temperature limit of 30°C was best TheSWBT strategy with a target temperature of 9°C was a closesecond However, the weather conditions for the thirdharvest date were such that anyone of the top four rankscould be the preferred one to use for Dodge City conditions.Unlike for the earlier selection of the preferred drymgl

conditiomng strategy for this location, several storage

strategies representmg Sentry PAC® , SWBT and chilledaeration ranked highly across the three harvest dates. Theoverall ranking for the entire penod placed chilled aeration

Table 3. Storage season fmal selection for Dodge City, KS

first, Sentry PAC® second, and SWBT third (Table 3).Given the closeness of the ranks for the chilled and Sentry

PAC® aeration strategies, their critical vanables werecompared in a 29 year SImulationrun DMLwas 39% higher

in the Sentry PAC® strategy compared to chilled aeration

for all of the harvest dates. The Sentry PAC® averaged12.5% bin moisture while chillmg was slightly lower at12.4%. However, insect rates climbed by 94% for Sentry

PAC® aeration, while chillmg maintained insectdevelopment below 50,000 umts per bin for all harvestdates. This required an energy consumption ofapproximately 2.25 kWhlbu for chilling whereas the Sentry

PAC® used less than 0.25 kWhlbu for the storage penodGiven the results of the 29 year Simulations, it was decidedto select chilling for all harvest dates at Dodge City becausethe benefits of non-chemical insect control were assumed tooutweigh the costs for popcorn based on previous research(Rulon, 1996). Insect development and DML were limited

while shnnk was comparable to the Sentry PAC® systemAdditionally, it was assumed that chilled aeration could befurther optimized by reducing the frequency of rechillmg ,and thus shnnk loss and energy consumption

Product of Fmal SeasonConditioning Strategy September 1 September 15 October 1 Years Ranks Ranking

Chill 2 1 4 8 1Sentry, TMC 18.5%, T < 20°C 1 3 3 9 2Swbt < 11 MaxMCof 14.5% 3 4 5 60 3

Fort wayne

For October 1, all of the top ten strategies for each

weather year (good, normal, poor) were Sentry PAC®aeration strategies When ranked across years, the overallstorage strategy selected for this first harvest date had atarget moisture of 18.5 % and a temperature limit of15.6°C. For October 15 mne out of the top ten strategies m

each of the weather years were Sentry PAC® aerationstrategies. Although target moistures of 17.5 and 18.5 %

compared closely, the Sentry PAC® strategy that wasselected as the preferred storage strategy for this harvestdate had a target moisture of 18.5 % and temperature limit

of 15.6°C. For November 1 the Sentry PAC® aerationstrategies With the 17.5 % and 18.5 % target moistureschemes were the best. The preferred storage strategy hada target moisture of 18.5 % and temperature limit of 30°C,which was a higher setting then for the other two harvestdates.

In the selection of the preferred storage strategy for the

Fort Wayne location, a total of SIXSentry PAC® aerationstrategies were ranked across the harvest dates (Table 4).

The best Sentry PAC® strategy for Fort Wayne had a targetmoisture of 18.5 % and a maximum temperature limit of15.6°C This strategy placed first m both the October 1 and15, and third in the November 1 harvesting penods. A 29year Simulation analysis was run for the two top Sentry

PAC® aeration strategies to confirm the correcttemperature limit choice DML, energy consumption andinsect populations were all higher for the 30°C temperaturelimit compared to 15. 6°C. Shrmk loss was lower but thedifference between the lower and upper temperature limitswas only 0 - 0.5 points. Surpnsmgly , nonuruforrruty wasfairly consistent between the two temperature limits despitethe difference m shnnk loss. GIven these results, nosigmficant benefit could be attributed to choosing a highertemperature limit. Thus, a maximum temperature limit of15.6°C was chosen for all harvest dates for Fort Wayne.

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Proceedmqs of the 7th International Working Conference on Stored-product Protectwn - Volume 2

Table 4. Storage strategy season fmal selection for Fort Wayne, IN.

Conditioning Strategy October 1 October 15 November 1Product of Fmal SeasonYears Ranks Ranking

Sentry, TMC 18.5%, T < 15.6°C 1 1 3 3 1

Sentry, TMC 18.5%, T < 30°C 3 2 1 6 2

Sentry, TMC 18.5%, T < 20°C 5 4 2 40 3

Sentry, TMC 17.5%, T < 156°C 2 5 6 60 4

Sentry, TMC 17.5%, T < 30°C 6 3 4 72 5

Sentry, TMC 18.5%, T < 20°C 9 7 5 315 6

Summary

Unlike for the conditiomng phase, a single site-specificstorage strategy was found to be the 'best' for all harvestdates for both Dodge City and Fort Wayne Based on over700 simulation runs, chilled aeration Yieldedthe best resultsgiven Dodge City weather conditions. The chilled aerationstrategy maintained average DML below 0.5% over theentire storage penod regardless of initial conditionmg startdate. Shnnk loss increased slightly while nonuniformitydecreased from the September 1 to October 1 harvest dates

~ '~...s ... ,,~~~~ _ ,,",M$"1U>""'~IM"'''

5 OE+04

45E+04

j 40E+04

I 35E+041

f30E+04 P

I 25E+04}20E+04

~

15E+04

10E+04

50E+03 ,I--' t- f--

~If

Given the warm conditions at Dodge City during the fall, aclulled aeration cycle was required for the September 1harvest date. Average energy consumption for September 1over the 29 years equaled 3.52 kWhlBu However, theSeptember 15 and October 1 harvest dates decreased energyusage by 54%, respectively, because conditions did notwarrant chilled aeration m the fall. Overall, insectpopulations were reduced below 30,000 units for the entirestorage period, which was well below the FGIS limit of400,000 umts per bin (51 miurous insects per bushel)(Figure 1). The rechillmg frequency for the summerstorage needs to be further optimized, however.

N

t-- Gr- 1---l1l1I--------

}---l:U--{-:j--f"i-~ 1---tr;lJ--HI---tlil--I. '1-~ .. --n11---ll1----l J-~~-M--m----lili-t t- .,1- I- I-

!~

Fig. 1. Total insect populations for dulled aeration followmg the natural air drymg strategy for the September 1 HD for DodgeCity, Kansas (G=1972; N=1974; P=1963; FGISLlmlt=400,OOO uruts per bm)

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Proceedmqs of the 7 th Internatumal Worktng Conference on Stored-product Protectum. - Volume 2

Sentry PA(® aeration WIth a target moisture content of18.5% and a maximum temperature limit of 15. 6"C yieldedthe best results given Fort Wayne weather conditions. The

Sentry PAC® aeration strategy contained average DMLbelow 0.5 % regardless of the harvest date. Shrink loss wasbelow 0.5 pomts while nonumformity slightly increased asthe harvest date was delayed over the 29 years. Averageenergy consumption for all harvest dates was 0.14 kWhlbu.In general, a majonty of the 29 years had endmg storageinsect populations below the FGIS Iimit of 400,000 umtswith the exception of two-three years (Figure 2) Failureyears point to the importance of preventive pestmanagement, which includes monitoring of msect

populations with pitfall and pheromone traps mside storagebins. When economic threshold levels are reached,fumigation of the infested popcorn will be necessary tocontrol these outbreaks during the summer storage period.Given the fact that popcorn IS for human consumption,

processors routinely fumigate a bm before unloadmg,processing and packaging. The aeration storage managementstrategies selected for Dodge City (chilled aeration) andFort Wayne (Sentry PAC aeration) will allow processors toehmmate calendar-based fumigation treatments. This willlimit their need for fumigation to a one-time treatment tokill all insect species and hfe stages before processmg, andto threshold-based treatments during failure years based onmtegrated pest management (IPM) principles.

, 16E+06 ---

14E+06 -i---------------------------11--------4

1 2E+06 -l-------------------------il--------,

1OE+06 +---------------------------11--------,

80E+05 +------------------------ ...-------,

60E+05 +------------------------il--------,

N40E+05 -1--------------------------iI------1t---t

2 OE+05 +----=--------- .....--t\\li1----R---=::-i ~-----I

p

Fig. 2. Total Insect population results for Sentry PAC® aeration followmg the EMC wmdow 12 - 24% for the October 1 lID forFort Wayne, Indiana (G = 1990; N = 1972; P = 1987; FGIS Lmut = 400 ,000 units per bin)

References

Adams, W. H. 1994. Development of a prototype post-harvest aeration and storage trainer. Unpubhshed M. S.Thesis. Purdue University.Bailey, J. E. 1992. Whole grain storage. In: Storage ofCereal Grains and their Products. Christensen, C. M.(eds. ). AACC. St. Paul, MN. pp. 157-182.

Flood, C A and G M. WhIte. 1984 Desorptionequilibnum moisture relationships for popcorn. Trans. ofthe ASAE. 27: 561 - 565, 571.Gann, R. 1996. Indiana agriculture - September Issue.Indiana Agricultural Statistics Service. Purdue University.West Lafayette, IN.Hagstrum, D. W. and J. E. Throne. 1989. Predictability ofstored-wheat insect population trends from life historytraits. Environ. Entomol. 18: 660 - 664.

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Proceedings of the 7th International Working Conference on Stored-product Protection - Volu?ne 2

Hanes, R. E. 1973. Evaluation of specific gravity, densityand popping moisture of popcorn. Unpublished M. S.Thesis. Purdue University. West Lafayette, IN.Haugh, C. G. , R. E. Lien, R. E. Hanes and R. B. Ashman.1976. Physical properties of popcorn. Trans. of theASAE. 19: 168-171, 176.Mater, D. E. 1992. The chilled aeration and storage ofcereal grains. Unpublished Ph. D. Thesis. Michigan StateUniversity. East Lansing, MI.Maier, D. E., F. W. Bakker-Arkema and S. G.Ilangantileke. 1993. Ambient and chilled aeration underThai conditions. Agric, Engng. J. 2: 15 - 33.Maier, D. E. 1996. Preservation of grain with aeration. pp.379 - 397. In: Grain Drying in Asia. Champ, B. R., E.Highley and G. I Johnson. (eds. ). Australian Centre forInternational Research Proceedings No. 71. Canberra,Australia. 1996.Montross, M. 1997. PHAST revisions. PersonalCommunication. Purdue University, West Lafayette, IN.Mullen M. A. and R. T. Arbogast. 1984. Low temperatureto control stored product insects. In: Insect Managementfor Food Storage and Processing. pp. 257 - 264. Baur, F.J. (eds.). MCC. St. Paul, MN.Popcorn Institute, The. 1995. Popcorn industry fact sheet.Chicago, 11.Rulon, R. A. 1996. In-bin conditioning and pestmanagement of popcorn using chilled aeration.Unpublished M. S. Thesis. Purdue University.Ruffner, James. 1985. Climates of the states. 3rd eds.National Oceanic and Atmospheric Administration. NCOC.Asheville, NC. Gale Research. Detroit, MI. pp. 334 - 58,

401- 34.Sentry Technologies, INC. 1993. Operator's manual. 1389Park Road. Chanhassen, MN. 55317.Stroshme, R. L., McKenzie, B. A., Sarwar, G.,Thompson, T. and McFate, K. L. 1992. Improvingmanagement of low temperature drying of corn. TR-100445 Research Report 2782-04. Electric Power ResearchInstitute, Palo Alto, CA.Thomas, Wilham. 1997. Methyl Bromide information.www.epa. gov. Office of Atmospheric Programs.Stratospheric Division.White, G.M., I. J. Ross and C. G. Poneleit. 1981. Fully-exposed drying of popcorn. Trans. of the ASAE. 24: 466-468,475.

Willer, J. G. and A. M. Brunson. 1927. Factors affectingthe popping quality of popcorn. J. Ag. Res. 35: 615-624.Wilson, S. G. and J. M. Desmarcheher. 1994. Aerationaccording to seed wet-bulb temperature. J. Stored Prod.Res. 30: 45 - 60Zink, D. J. 1998. Optimization of Popcorn Conditioning andStorage Strategies. Unpubhshed M. S. Thesis. PurdueUniversity.Zink, D. J., Montross, M. D. and Maier, D. E. 1997.Evaluation of site-specific drying and conditionmgstrategies for stored popcorn. Paper No. 97-6067. ASAE,St. Joseph, MI.Zink, D. J., Montross, M. D., Maier, D. E. and Mason,L. J. 1998. Evaluation of site-specific pest and qualitymanagement strategies for stored popcorn. Paper No. 98-6046. ASAE, St. Joseph, MI.

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