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Thermal Process Development of a Home-Canned Salsa-Type Product

E. M. D'sa and E. L. Andress, Dept. of Foods & Nutrition, University of Georgia, 208 Hoke Smith Annex, Athens, GA 30602-4356.

Paper 33C-10. Presented at the Institute of Food Technologists Annual Meeting, Las Vegas, NV, July 14, 2004.

Abstract

Adequate thermal treatment in home-canned products ensures product safety from pathogens including Clostridium botulinum, eliminates the risk of spoilage microflora outgrowth and ensures product shelf-stability.

The objective was to experimentally calculate a thermal process recommendation for home canning of an acid salsa-type product and to determine the effect of consumer procedural variations on product heat penetration patterns.

An original standardized cranberry salsa (equilibrium pH 3.1) was filled into pint home canning jars. The cold spot was determined with thermocouples inserted through two-piece canning lids, to monitor temperatures at each of five potential cold spots in eighteen canner loads. Sealed jars were placed in a boiling water canner and temperatures recorded using Ellab™ software, through come-up, cool down, and a processing time that ensured that all jars reached a minimum of 2°C below processing temperature. Analyses of f(h) values (slope of the straight line portion of a heating curve) located the cold spot at the geometric center of the jar. Product cold-spot temperatures were then monitored through canning processes that produced a minimum temperature of 90.5°C, for standard filling procedures and variations of high-fill weight and low-initial temperature procedures.

A calculated 10 min boiling water process ensures adequate thermal treatment for this product. Up to a 10 minute post-cook lag prior to filling jars, and up to a 30g increase in product fill weight did not significantly change f(h) values, when compared with the standard treatments.

Home canning is a significant means of food preservation in some U.S. households, utilizing seasonal produce and in some cases contributing to food security. Confidence in thermal processing methodology recommendations is necessary for novel ethnic-type products. This paper presents data on thermal processing studies carried out on a conduction-heating food item and explains the effects of procedural variations inadvertently introduced during the canning process.

Introduction

The demand for novel home-canned products is constantly increasing, especially those using unusual food items, and those prepared and used in novel ways (Andress, 2001). The objective of this project was to develop a new salsa product using cranberries, and determine an adequate thermal process that would make the salsa not only highly palatable for independent use or in combination with other foods, but also safe when home-canned under recommended home-canning conditions.
The cranberry salsa is an acid food (pH < 4.6), and thus the primary concern was to ensure the development of a standardized product, prevent spoilage from acid-resistant microorganisms and produce an adequate jar vacuum seal.

Ingredients and Preparation Process

Spicy Cranberry Salsa:
Ingredients: 6 cups chopped red onion, 4 finely chopped large Serrano peppers*, 1½ cups water, 1½ cups cider vinegar (5%), 1 tablespoon canning salt, 1-1/3 cups sugar, 6 tablespoons clover honey, 12 cups (2¾ pounds) rinsed, fresh whole cranberries.
*Caution: Wear plastic or rubber gloves when handling and cutting hot peppers or wash hands thoroughly with soap and water before touching your face or eyes.

Yield: About 6 pint jars.

Procedure:
   1.   Wash and rinse 6 pint canning jars; keep hot until ready to use. Prepare lids according to manufacturer's directions.
   2. Combine all ingredients except cranberries in a large Dutch oven. Bring to a boil over high heat; reduce heat slightly and boil gently for 5 minutes.
   3. Add cranberries, reduce heat slightly and simmer mixture for 20 minutes, stirring occasionally to prevent scorching.
   4. Fill the hot mixture into clean, hot pint jars, leaving ¼-inch headspace. Leave saucepot over low heat while filling jars. Remove air bubbles and adjust headspace if needed. Wipe rims of jars with a dampened clean paper towel; apply two-piece metal canning lids.
   5. Process in a boiling water canner.

Thermal Process Development

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 18 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 (450g, 480g) and two fill temperatures (direct-fill, and after a 10 minute wait, which had means of 84.4° and 80.4°C, respectively. Process calculation was accomplished by using thermocouples in each of six jars in different canner loads of each of the three fill methods (standard, low initial temperature, and high-fill weight). These jars were processed to 90.5°C plus an additional 5 minutes.
Processing was done in a boiling water canner using the stovetop burners of a household gas range (Frigidaire Gallery Model ES III. 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<.001) differences existed between the treatments using the General Linear Model procedure in SAS 8e (1999-2001).

Results

Cold Spot Location
  • The cold spot for this product and jar combination was located at the geometric 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: Cold Spot Determination of Cranberry Salsa in Pint Jars
Thermocouple height in pint jar Average f(h) value
n = 18
Range Standard Deviation
Center 54.86¹ 48.5 - 73.4 5.3
½" Below Center 53.89 48.6 - 64.7 3.9
1" Below Center 51.94 45.8 - 64.9 4.8
1½" Below Center 48.98 43.0 - 60.8 4.7
2" Below Center 47.00 41.4 - 58.0 4.5
¹Location 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 82.0-82.5°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 77.81-90.19°C in the standard series.
  • There was greater variability among initial temperatures in the series used for HFW (overfill) and LIT (low initial temperature) calculations, but this difference did not effect the interpretation of findings or the ultimate process recommendation.
Table 2: Thermal Characteristics of Jars Processed by Three Methods
  Procedures
Standard
n=12
Overfill
n=30
Low Fill
Temperature
n=18
Total Fill Weight 450 g 480 g 450 g
  °C °C °C
Canner Initial Temperature 81.86 ± .048 82.14 ± 0.27 82.14 ± 0.04
Jar Initial Temperature¹ 84.4 ± 3.9 87.5 ± 3.3 80.4 ± 3.1
Jar Temperature at Start of Boiling 80.67 ± 2.0 82.28 ± 2.3 78.29 ± 2.07
    Temperature change during come-up time - 3.73 - 5.22 - 2.11
Jar Temperature at the end of experimental process² 93.16 ± 0.63 93.19 ± 0.63 93.13 ± 0.75
    Maximum temperature change during process + 8.76 + 5.69 + 12.73
¹ Heat penetration data for 12-30 jars were collected from 3-5 different canner loads
² Heat penetration data were collected by allowing the slowest-heating jar to reach 90.5°C plus an additional 5 minutes


Determination of the Calculated Thermal Process
  • Pflug(1998) outlines guidelines for thermal process calculations, based on the equilibrium pH of the product. This is then correlated to a in minutes, based on product pH. Since the equilibrium pH of the cranberry salsa product is 3.1, according to process development guidelines a minimum of 0.1 minutes is enough to ensure an appropriately canned product.
  • The of 0.1 minutes for the cranberry salsa is achieved within the come-up time of the product, itself.
  • Thus, a 10 minute process time was determined for the product, this time would be sufficient to achieve the desired lethality, as well as ensure a proper vacuum seal for the jar lid and sterilization of the glass jar (Table 3).
Table 3: Recommended Process Time for Spicy Cranberry Salsa in a Boiling-Water Canner
Style of Pack Hot    
Jar Size Half-pints or Pints    
 
Altitude 0-1,000 ft 1,001-6,000 ft Above 6,000 ft
 
Processing Time 10 min 15 min 20 min


Effect of Fill Weight and Initial Jar Temperature
  • An increased fill weight (up to 30g over the standard pint jar fill weight) had no significant effect on the f(h) values and thus thermal process, for the cranberry salsa product in pint jars.
  • A 10 minute pre-fill cooling time (which resulted in a mean 4°C temperature difference) had no significant effect on f(h) values and thus the thermal process, for the cranberry salsa product in pint jars.
  • Both procedural variations of increased fill weight and lowered initial jar temperature had no significant effect on the final product temperature at the end of the process.
  • A 4°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 4).
Table 4: Effect of Fill Weight and Fill Temperature on Heat Penetration by Three Methods
  Procedures
Standard
n=12
Overfill
n=20
Low Fill
Temperature
n=18
Total Fill Weight 450 g 480 g 450 g
Jar Initial Temperature (°C) 84.4 ± 3.9 87.5 ± 3.3 80.4 ± 3.1
f(h) 60.40 ± 1.1 59.97 ± 1.6 59.58 ± 1.6
Average Minutes to Reach 90.5°C at Boiling¹ 22.83 ± 2.5 20.83 ± 3.3 25.05 ± 2.9
¹ Time 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.

Summary and Conclusions

  • An increase of 30 grams product per pint jar did not significantly increase the heat penetration rate (fh).
  • A decrease of 4°C in the initial fill temperature did not change the heat penetration rate (fh) or processing time for this product.
  • Canning instructions should be specific for the product composition, jar dimensions, and number of jars per recipe.

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. Garner, H. H. and Andress, E.L. 2002. Effect of fill weight and initial temperature on processing time for a home pickled jicama relish. Poster presented at IFT Annual Meeting, Anaheim, CA.
   3. Pflug, I. J. 1998. Microbial Control Processes for Acid Foods. In Microbiology and Engineering Processes. Environmental Sterilization Laboratory, Minneapolis, MN
   4. Statistical Analysis Software, v. 8e. 1999-2001. 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. E. M. D'sa and E. L. Andress. 2004. Thermal Process Development of a Home-Canned Salsa-Type Product. 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.

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The University of Georgia
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