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Studies on safe acidification of salsa for home boiling water canning

B. A. Nummer, M. Thacker, E. M. D'Sa, and E. L. Andress, Dept. of Foods & Nutrition, University of Georgia, 328 Hoke Smith Annex, Athens, GA 30602-4356.

Paper 33C-9. Presented at the Institute of Food Technologists Annual Meeting, Las Vegas, NV, July 14, 2004.

Abstract

Salsa is America's No. 1 condiment. This popularity has extended to home food preservers who want to make use of a seasonal harvest of garden-grown tomatoes and vegetables. Most salsa recipes mix low-acid foods, such as onions, green peppers, and jalapeño peppers, with acid foods, such as tomatoes. Currently the USDA and the National Center for Home Food Preservation recommends that a boiling water canning process be used only for research-tested salsa recipes that provide evidence of safe acidification to inhibit Clostridium botulinum growth. Only a few such research-tested salsa recipes are available and these must be followed with little deviation.

This project sought to create and test a guideline recipe for salsa that allowed for variations in low-acid ingredients, while maintaining a safe level of acidification from tomatoes and lemon juice.

Based on this research a safe recipe guideline ratio of 200 g Roma tomatoes, 200 g (onions, peppers, and dry spices), and ¼ cup (60 ml or 61g) of bottled lemon juice per pint volume was proposed. The lemon juice (60 ml) safely acidified a lab recipe (200 g Roma tomatoes, 120 g onions, 65 g green peppers, 15 g jalapeño peppers, and 5 g table salt per pint) to below pH 3.82. Salsa made from 200 g tomatoes, cup lemon juice and either all onions (200 g) or all green peppers (200 g) as the low-acid ingredient maintained a pH below 3.82. In acidification curves single low-acid salsa ingredients needed only 10 ml lemon juice per 200 g vegetable to acidify below pH 4.6. Furthermore, 60 ml lemon juice per pint safely acidified full pint volumes (263-304 g) of onions, green peppers, or jalapeños alone to below pH 3.82. Informal taste panels indicated an acceptable salsa flavor after canning using recipes within the guideline.

Introduction

Most tomato-based salsa recipes mix low-acid foods, such as onions, sweet and/or hot peppers, with acid foods, such as tomatoes. Currently the USDA (2) and the National Center for Home Food Preservation (http://www.homefoodpreservation.com) recommend that a boiling water canning process be used only for research-tested salsa recipes that provide evidence of safe acidification to inhibit Clostridium botulinum growth. The USDA Complete Guide to Home Canning (2) has only one salsa recipe. Research by Hillers and Dougherty (1) created six more salsa recipes for home canning and these have been attached to the USDA Complete Guide to Home Canning by Utah State University as an addendum to Guide 3. Hillers and Dougherty note the only safe changes a home food preserver can make to their listed recipes is to substitute bottled lemon or lime juice for vinegar or to change the amount of spices and herbs. This project sought to create and test a guideline recipe for salsa that allowed for minor variations in low-acid ingredients, while maintaining a safe level of acidification from tomatoes and lemon juice.

Materials and Methods

Figure 1. Guideline Salsa Recipe ~ per pint jar

  • ¼ cup lemon juice (60 ml)
  • 200 g Roma tomatoes (peeled, deseeded, and diced to approx. ¼") ~ tomato juices were drained and discarded
  • 200 g any combination of onions, bell peppers (diced to approx. ¼") and pureed hot peppers including seeds
  • ¼ tsp salt
Processing: All of the ingredients were combined in a saucepan and brought to boil over medium heat with stirring. The heat was reduced and the salsa was simmered for three minutes. Salsa was packed into clean, hot, pint-size canning jars leaving a ½ inch headspace.

Boiling water processing: Jar rims were wiped and standard metal two-piece lids were added; then the salsa was processed for 15 minutes in a boiling water canner using the standard consumer methods referenced in the USDA Complete Guide to Home Canning (2).

Ingredients

All foods were obtained from a national grocery chain. Vegetables were of high quality (no bruising, firm and disease free) and were kept refrigerated until use. Acidifying agents were ReaLemon® juice or ReaLime® juice, and Kroger® brand 5% acetic acid vinegar.

Tomatoes were dipped in boiling water for 1-2 minutes until the skins wrinkled, then submerged into cold water. Loose skins were peeled off. Tomato flesh was cored, cut into pieces, and deseeded. The pieces were then cut into approximately ¼ inch cubes and the juices drained off through a colander. Onions and peppers were cut into approximately ¼ cubes. De-stemmed jalapeño peppers were puréed including seeds to maintain the capsaicin.

Acidification of a tomato, onion, and pepper salsa

Diced salsa ingredients (200 g Roma tomatoes, 120 g sweet onions, and 65 g sweet peppers), 15 g puréed jalapeño pepper, and 5 g salt were cooked with (¼ - 3/8 cup) vinegar, lemon juice or lime juice and canned in pint jars. The mixture was cooked, packed into hot pint jars, capped, and processed for 15 minutes (Figure 1.). After 24 h the product pH was determined from blended solids and brine. The goal was to obtain a quality product with a pH below 4.0 and closer to pH 3.8.

Acidification of individual ingredients by lemon juice

Lemon juice (0, 5, 10, 15, 20, 25, and 30 ml) was added to 100 g (¼" cubed) sweet green peppers, Roma tomatoes, white onions and hot (jalapeño) peppers. Each vegetable was placed into a half pint canning jar with the measured amount of lemon juice, and tap water to reach a ½" headspace. Three jars of each treatment were measured. Jar contents were cooked, repacked into hot jars, capped, and processed for 15 minutes (Figure 1.). After cooling overnight pH measurements were taken.

Measurement of pH

An Orion 520 A+ pH meter was used for all measurements. Readings were an average of three measurements made in different locations of the sample. A brine pH was determined by inserting the probe directly into the jar and reading the pH. A solids pH was determined for both un-rinsed solids and rinsed solids. The solids were drained in a U.S. standard No. 8 sieve inclined at a 17-20 degree angle for two minutes. For rinsed solids, 15 ml tap water was sprayed over the solids on the sieve and allowed to drain. Un-rinsed or rinsed solids were blended and the pH measurement was taken.

Acidification of pepper and onion varieties by lemon juice

Three varieties of sweet bell peppers (yellow, green and red) and three varieties of onions (yellow, white and purple) were cut into ¼ inch sized cubes and 200 grams of each were added to pint mason jars. Lemon juice (¼ cup) was added. Tap water, if needed, was used to top jars to a ½ inch headspace. Jar contents were cooked, repacked into hot jars, capped, and processed for 15 minutes (Figure 1.). After cooling overnight pH measurements were taken.

Acidification of excess quantities of low acid vegetable by lemon juice

Three varieties of sweet bell peppers (yellow, green and red) and three varieties of onions (yellow, white and purple) were cut into ¼ inch sized cubes. The maximum volume of vegetable was pressed into pint mason jars allowing for a ½" headspace; fill weights were recorded. Lemon juice (¼ cup) was added. Tap water, if needed, was used to top jars to a ½ inch headspace. The jar contents were cooked, packed into hot jars, capped, and processed in a boiling water canner for 15 minutes (Figure 1.). After cooling overnight pH measurements were taken.

Results

Acidification of a tomato, onion, and pepper salsa

Table 1: Salsa pH vs. Type and Amounts of Acid
Acid Salsa pH* Notes
  3/8 cup ¼ cup 1/8 cup  
Vinegar 3.81 4.23 4.48 Has unappealing vinegar taste
Lemon Juice   3.83   Has a very mild lemon flavor
Lime Juice   3.81   Lime flavor is evident, but would be appropriate to salsa
* 24-hour pH of blended product (solids and brine).
  • Lemon and lime juice (¼ cup per pint) provided the best acidification of the salsa to pH 3.8 4.0. Lemon juice had a milder flavor, while lime juice provided a lime flavor that would be appropriate to this type of salsa. Lemon juice was chosen to continue experiments.

Acidification of tomatoes, peppers, and onions by lemon juice

Lemon juice acidification curves were created for sweet green peppers, Roma tomatoes, white onions and hot (jalapeño) peppers (Figures 1A-D.).

  • Lemon juice (15 ml) safely acidified 100 g of each vegetable to below pH 4.0. Brine and solids pH measurements were nearly identical indicating acid equilibration within the 24 h period. When 30 ml of lemon juice was added to 100 g of vegetable the pH was safely reduced for: sweet green peppers (pH <3.43), Roma tomatoes (pH <3.38), white onions (pH <3.44) and hot (jalapeño) peppers (pH <3.73).
  • It was interesting to note that this skinned and deseeded Roma tomato flesh had a pH of 4.6-4.7. This was most likely due to loss of acid in the tomato juice that was intentionally not used to avoid a watery salsa.
  • The data suggest that 30 ml bottled lemon juice will safely acidify 100 g of tomatoes, peppers, or onions; or some combination of these ingredients.

Acidification of full pint volumes of onions, green peppers and jalapeño peppers

Full pint volumes of low acid vegetables (onions or peppers) were combined with ¼ cup of lemon juice (60 ml) to determine if consumer error could lead to unsafe acid levels in the guideline salsa recipe. Several varieties of onions were packed tight into a pint jar and weighed. From 263 295 g fit into jars from nine replicates. The maximum pint volume of green peppers weighed from 296 304 g for three replicates. After adding lemon juice, cooking, and boiling water processing, the full pint volumes of acidified onions had a pH range from 3.59 3.82 and full pint volumes of acidified green peppers had a pH range of 3.66 3.80 (data not shown).

Acidification of tomatoes, peppers, and onions by lemon juice and Roma tomato

The experimental salsa recipe allows consumers to vary the quantity of low acid ingredients (onions and peppers) from 0-200 g per pint of salsa. Thus the acidification of single low acid vegetables by 200 g Roma tomato and ¼ cup lemon juice was examined

Table 2. pH of salsa made with 200 g Roma tomato,
¼ cup lemon juice and 200 g of single low acid vegetables
Vegetable (pH) Corresponding salsa pH*
White onions (5.60) 3.88 - 3.82
Yellow onions (5.71) 3.76 3.81
Spanish Red Onions (5.50) 3.75 3.82
Green Peppers (5.62) 3.75 3.81
Red Peppers (5.08) 3.74 3.79
Yellow Peppers (5.53) 3.81 3.82
* 24-hour pH of blended product (solids and brine).

Discussion

  • Lemon juice (¼ cup or 60 ml) safely acidified a guideline salsa recipe containing 200 g Roma tomatoes, 120 g onions, 65 g peppers, 15 g hot pepper purée, and ½ tsp salt to a pH below 4.0. The flavor and color of this salsa after canning was of acceptable quality based on preliminary tests.
  • Lime juice provided the same acidification of the salsa, but it had a much stronger lime flavor and aroma.
  • A larger volume of vinegar was needed to achieve equivalent pH values for the salsa mixture; this volume resulted in a pronounced flavor change.
  • Acidification curves indicated that lemon juice (30 ml per 100 g vegetable) could safely acidify tomatoes, peppers, or onions prepared under the conditions in this experiment.
  • Salsa made from 200 g Roma tomatoes, ¼ cup bottled lemon juice and either all onions (200 g) or all green bell peppers (200 g) was safely acidified.
  • Using the correct amount of bottled lemon juice (¼ cup per pint) full pint volumes of either onions or bell peppers are safely acidified. This helps provide a safer recipe despite the possibility of consumer error.
  • This recipe is not yet being recommended for public use until there is further research and peer review. Validation with more replications and in larger batch recipes and heat penetration studies are needed. The final goal is a recipe that could be validated to allow consumers some measure of creativity in mixing their low-acid ingredients in a tomato-based salsa to maintain safe acidification for boiling water canning.

References

   1.   Hillers, V.A. and R. Dougherty. 1996 (revised 2000). Salsa Recipes for Canning. Washington State University Cooperative Extension Service.
   2. USDA. 1994. USDA Complete Guide to Home Canning. Agriculture Information Bulletin No. 539. Available at: http://www.uga.edu/nchfp/publications/usda/utah_can_guide_00.pdf. Accessed 10 Jul 2004.



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. B. A. Nummer, M. Thacker, E. M. D'Sa, and E. L. Andress. 2004. Studies on safe acidification of salsa for home boiling water canning. 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

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