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Effect of Fill Weight and Initial Temperature on
Processing Time for a Home Pickled Jicama Relish

H.H. Garner and E.L. Andress, Department of Foods and Nutrition, The University of Georgia, 208 Hoke Smith Annex, Athens, GA 30602-4356.

Paper 46B-6. Presented at the Institute of Food Technologists Annual Meeting Anaheim, CA, June 17, 2002.

Abstract

Pickled vegetables are popular home preserved condiments. The increasing variety of produce in the marketplace offers opportunities for greater diversity in condiments such as salsa and relishes than has traditionally been available in the U.S. Jicama was studied for its potential use in home pickled products with a crisp texture. The objective of this study was to determine the effect of typical consumer procedural variations on heat penetration when processing an acidified jicama relish recipe. Variations were made in fill weight and initial temperature (IT) of the filled jars. An original recipe with an equilibrium pH of 3.5 was developed for heat penetration studies using a hot pack, pint jars and boiling water canner. Product temperatures were continuously recorded at the predetermined cold spot throughout come-up time, 35 minutes in boiling water, and air cooling of jars. Fifteen jars (five jars in each of three canner loads) were used for each procedural variation of fill weight and IT. Processing was done in a 17-quart boiling water canner on a household gas range. Fill weight had a significant impact on both maximum jar temperature obtained and final process time recommendation. Heat applied during come-up had no effect on jar temperature with the overfill. A decrease of 5°C (64.5 vs. 69.7) in IT had no effect on either maximum jar temperature reached at the end of come-up or the 35 minutes at boiling. However, analysis of the maximum jar temperature reached at the end of come-up or the 35 minutes at boiling. However, analysis of the worst case low IT jar would result in a longer process time than for the higher IT product. This study documents the effects of some consumer practices on process lethality for a cubed relish product. Overfills should be avoided to insure expected heating rates and final maximum temperatures. Specifying a minimum number of jars to a home canning recipe could be considered.

Introduction

  • Pickled products are low acid foods that have had their pH lowered to 4.6 or below by the addition of acid or vinegar before thermal processing in order to produce a safe product.

  • A USDA survey of home canning practices in the 1970's (Davis and Page, 1979) indicated that 20% of home canners make products with combinations of acid and low acid ingredients and use inappropriate methods for processing; a 2000-2001 survey by the University of Georgia had similar findings (Andress, 2001).

  • Improperly formulated pickled products may allow for growth of the organism C. botulinum, which leads to toxin formation and the potentially fatal food intoxication, botulism.

  • Improperly processed pickled products may allow room for the growth of mold, yeast and/or bacteria that produce spoilage.

Hypotheses

  1. As fill weight of jars increases, the f(h) value and required processing time will increase.
  2. As initial fill temperature of jars decreases, required processing time will increase.

Methods

A thermal process (home canning) recommendation was developed for pint jars of an original pickled vegetable relish (jicama, red and yellow bell peppers, onion, hot pepper, spices and vinegar/sugar brine), see Figure 1 (Garner and Andress, 2001). Determination of the cold spot for this product and jar combination was made using data collected for heat penetration curves at 5 potential cold spot locations in the jars in 12 canner loads, see Table 1.

Two levels of two procedural variations were used in testing for process calculations. Temperature profiles were compared for two fill weights (454g, 490g) and two fill temperatures (69.7°C, 64.5°C) of the relish. A total of 12 to15 data points (replications) at the determined cold spot were used for the process calculation. This was accomplished by using thermocouples in each of five jars in three different canner loads of each of the three fill methods (standard, low initial temperature, and overfill).

A total of 15 data points (replications) at the determined cold spot were used for the process calculation. This was accomplished by using thermocouples in each of five jars in three different canner loads of each of the three fill methods (standard, low initial temperature and overfill).

Processing was done in a boiling water canner using the stovetop burners of a household gas range (Magic Chef model 3267XTW). Data were recorded using an Ellab E-Val™ Monitoring System and software and Ecklund needle Type T copper-constantan thermocouples. Analysis of variance was used to determine if significant (p<0.01) differences existed between the treatments using the General Linear Model procedure in SAS 8.2 (2001).

Figure 1. Spicy Jicama Relish Recipe

9 c. diced jicama
1 Tbsp whole pickling spice
1 2-inch stick cinnamon
8 c. white 5% distilled vinegar
4 c. sugar
2 tsp. crushed red pepper flakes
4 c. diced yellow bell pepper
4-1/2 c. diced red bell pepper
4 c. chopped onion
2 fresh (about) 6” fingerhot peppers, finely chopped and partially seeded

  1. Wash, peel and trim jicama; dice.

  2. Place pickling spice and cinnamon on a double-layer of 100% cotton cheesecloth. Bring corners together and tie with a clean string.

  3. In a 4-quart Dutch oven or kettle combine pickling spice bag, vinegar, sugar, and crushed red pepper. Bring to boil, stirring to dissolve sugar. Stir in diced jicama, sweet peppers, onion and fingerhots. Return mixture to boiling. Reduce heat and simmer, covered, over medium-low heat about 25 minutes. Discard spice bag.

  4. Pack relish and syrup into 5 hot, clean pint jars, leaving ½-inch headspace. Wipe rims of jars; adjust two-piece metal canning lids. Process in boiling water canner.

Results

Cold Spot Location

  • The cold spot for this product and jar combination was located at 1½ inches below the center of the jar (Table 1).
  • The f(h) value is the number of minutes it takes the straight-line portion of the heat penetration plot to pass through one logarithmic cycle.
  • A larger f(h) represents a slower rate of heat penetration.
Table 1. Determination of Cold Spot Location
Thermocouple Height in Pint Jar Average
f(h) Value
Range Standard Deviation
  n = 12    
Center 29.5A1 24.6 - 34.1 2.9
½" Below Center 37.3B 32.3 - 41.4 2.9
1" Below Center 35.7B 30.7 - 40.2 2.9
1½" Below Center2 40.2B 37.2 - 44.0 1.9
2" Below Center 37.5B 34.4 - 43.6 2.8
1 Values with different letters in the same column are significantly different at p<.001.
2 Location of cold spot, as determined by largest individual f(h) value (worst-case scenario).

Thermal Characteristics of Jars Processed by Three Procedures

  • The initial canner temperature was consistently maintained at 82.0-82.7°C prior to the loading of filled jars (Table 2).

  • The initial temperature for this product as prepared and filled into jars by usual home canning practices ranged from 66.0-72.4°C in the standard series.

  • There was greater variability among initial temperatures in the series used for HFW (overfill) calculations, but this difference did not effect the interpretation of findingsor the ultimate process recommendation.
Table 2. Thermal Characteristics of Jars Processed by Three Methods
  Procedures
Standard
n=15
Overfill
n=12
Low Fill
Temperature
n=15
Total Fill Weight (Solids + Liquids) 454 g 490 g 454 g
Solids Fill Weight 354 g 472 g 354 g
  °C °C °C
Canner Initial Temperature (n=3)1 82.0 ± 0.6 82.7 ± 0.4 82.2 ± 0.4
Jar Initial Temperature 69.7 ± 2.0 73.2 ± 4.2 64.5 ± 2.0
Jar Temperature at Start of Boiling 80.4 ± 2.0 72.4 ± 2.5 79.5 ± 2.0
 Temperature change during come-up time + 10.7 - 0.8 +15.0
Jar Temperature after 35 Minutes of Boiling2 96.9 ± 0.5 91.3 ± 0.8 97.0 ± 0.3
 Maximum temperature change during process + 27.2 + 18.1 + 32.5
  Minutes Minutes Minutes
Maximum Time to Reach 90.5°C3 14 344 16
Recommended Process time (time at boiling)5 15 35 20
1 Heat penetration data for 12-15 jars were collected from 3 different canner loads.
2 Heat penetration data were collected for 35 mins once the canner was brought to boiling.
3 Values taken from worst-case individual jars; not averages.
4 One jar did not reach 90.5°C until two minutes into the cooling periood; its maximum temperature at the end of 35 minutes of boiling was 89.4°C.
5 Time needed to heat the product to 90.5° for one minute.


Effect of Fill Weight

  • The heat being applied during the come-up period (time it took the canner to come to a boil) had no effect on jar temperature with the overfill.

  • Fill weight had a significant impact on both maximum jar temperature obtained as well as the time at boiling required to reach a cold spot temperature of at least 90.5°C for one minute (Tables 2 and 3).

  • High fill weight significantly increased the f(h), indicating a slower rate of heat penetration (Table 3).

Effect of Initial Jar Temperature

  • A decrease of 5°C (69.7, 64.5) in the fill temperature resulted in no difference in either maximum jar temperature reached at the end of the come up period or the 35 minute boiling process (Table 2).

  • A 5°C decrease in fill temperature did not significantly change the number of minutes at boiling for the cold spot to reach 90.5°C (Table 3).

  • When a worst-case scenario approach is used there was a slight increase in the time at boiling needed to reach a cold spot temperature of 90.5°C in lower initial temperature jars (16 min. vs. 14 min.).

  • In practice, this finding would result in a longer recommended process time for the low initial temperature jars. Home canning recommendations are rounded up to the next 5-minute interval. The process time in the standard procedure would be 15 minutes; the recommended time for the low initial temperature practice would be 20 minutes.
Table 3. Effect of Fill Weight and Fill Temperature on Heat Penetration.
  Procedures
Standard
n=15
Overfill
n=12
Low Fill Temperature
n=15
Total Fill Weight (Solids + Liquid) 454g 490g 454g
Solids Fill Weight 354g 472g 354g
       
Jar Initial Temerature (°C) 69.7 ± 2.0A1 73.2 ± 4.2A 64.5 ± 2.0B
f(h) 33.5 ± 2.5A 61.1 ± 2.0B 34.6 ± 2.4A
Average Minutes to Reach 90.5°C at Boiling 2 11.3 ± 2.3A 34.8 ± 2.4B3 11.3 ± 2.4A
1 Values with different letters in the same row indicate a significant difference at p<.001.
2Time after water in canner returned to boiling. This comparison of averages is for statistical purposes; in practice, the process time would be determined by the slowest heating individual jar.
3One jar did not reach 90.5°C until two minutes into the cooling period; its maximum temperature at the end of 35 minutes of boiling was 89.4°C.

Summary

  • An increase of 118 grams solids per pint jar significantly increased the heat penetration rate (fh) and more than doubled the required processing time for this product.

  • A decrease of 5°C in the initial fill temperature did not change the heat penetration rate (fh) or processing time for this product.

Implications for Future Research and Practice

  • Canning instructions should specify a minimum number of jars to the recipe to avoid overfills.

  • It is possible that the recommended process time could be reduced if lethality during the cooling period is considered. Additional data would need to be collected to determine maximum jar temperatures reached with less than 35 minutes of boiling.

  • Results are limited to jar size and shape (conformation) used in this study.

  • If sensory evaluation testing in the future recommended any changes in the recipe that increased the equilibrium pH, heat penetration data and processing recommendations would need to be re-evaluated.

References

  1. Andress, E.L. 2001. A national survey of current home canning practices in the U.S. Athens, GA: National Center for Home Food Preservation, Department of Foods and Nutrition, The University of Georgia, Unpublished data.

  2. Davis, C.A. and Page, L.1979. Practices used for home canning of fruits and vegetables. UDSDA Home Econ. Research Report, No. 43. Washington, DC: Government Printing Office.

  3. Garner, H. H. and Andress, E.L. 2001. Effect of marinating procedure on pH of a pickled jicama relish. Undergraduate research study, Athens, GA: Department of Foods and Nutrition, The University of Georgia. Unpublished data.

  4. Statistical Analysis Software, v. 8.2 2001. Cary, NC: SAS Institute Inc.


This material is based upon work supported by the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture, under Agreement No. 00-51110-9762.

Document Use:

Permission is granted to reproduce these materials in whole or in part for educational purposes only (not for profit beyond the cost of reproduction) provided the authors and the University of Georgia receive acknowledgment and this notice is included:

Reprinted with permission of the University of Georgia. Garner H.H. and E.L. Andress. 2002. Effect of Fill Weight and Initial Temperature on Processing Time for a Home Pickled Jicama Relish. Athens, GA: The University of Georgia, Cooperative Extension Service.

References to commercials products, services, and information is made with the understanding that no discrimination is intended and no endorsement by the University of Georgia, U.S. Department of Agriculture and supporting organizations is implied. This information is provided for the educational information and convenience of the reader.

The University of Georgia and Ft. Valley State University, the U.S. Department of Agriculture and counties of the state cooperating. The Cooperative Extension Service, the University of Georgia College of Agricultural and Environmental Sciences offers educational programs, assistance and materials to all people without regard to race, color, national origin, age, sex or disability. An Equal Opportunity Employer/Affirmative Action Organization Committed to a Diverse Work Force.

Contact:

National Center for Home Food Preservation
208 Hoke Smith Annex
The University of Georgia
Athens, GA 30602-4356

Tel: (706) 542-3773
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