USDA 

 

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Module 13. Acidified Low Acid 

Foods 

Thermal Processing for Meat and Poultry 

Products Training 

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Purpose and Objectives 

 Purpose of Module 14 

• Provide concepts on acidification and 

methods to monitor and control. 

 Performance Objective 

• Can assess acidification procedures and 

determine if they are controlled and 

documented. 

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Introduction: Acidified Foods 

 Fermented foods preserved by lactic acid from 

bacteria 

 Preservation by addition of acid to low-acid 

ingredients 

 May be called “pickled foods” 

 Includes acidified and marinated vegetables 

 Excludes jellies, dressings, condiments, fermented 

foods, refrigerated foods, and naturally acid foods 

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Definition of Acidified Foods 

 An acidified food is a low-acid food to which 

acid or acid food is added to produce a final 

pH of 4.6 or less 

 Proper acidification prevents growth of C. 

botulinum 

 Final product pH must be 4.6 or less to 

prevent C. botulinum growth 

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Meaning of pH 

 pH is the term used to designate degree of 

acidity or basicity (alkalinity) 

 More hydrogen ions = more acidic 

 Scale ranges from 0 to 14 

 Values smaller than 7 mean more hydrogen 

ions or more acidic 

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Comparison of the Acidity of Pure Water with 

Representative Foods at Each pH Value 

 Pure water is neutral at a pH of 7.0 

 Above a pH of 7.0, there are more OH- ions 

 Below a pH of 7.0, there are more H- ions 

 The pH of beef, pork, and chicken is 

considered low acid 

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Buffering Capacity 

 Buffering capacity refers to the ability of a 

food to resist change in pH 

• Varies from food to food 

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Determination of pH 

Colorimetric Method Electrometric Method 

 Depends on color  Using a pH meter is 

change of dye most common method 

for determining pH

 Uses indicator solutions 

 Meters can be digital 

 Uses indicator or pH or analog 

paper 

 Provides only 

approximate values 

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pH Meter Electrodes (2) 

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n 

pH-sensitive 

glass 

membrane 

;-r Leads 

• 

Body 

• 

Calame! 

___.!...------- ref e re n c e 

electrode 

Use of pH Meter Electrodes 

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Combination Electrode 

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Electrodes 

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Precautions 

 Rinse electrodes to prevent cross-contamination 

 Do not wipe electrodes 

 Clean oily or greasy electrodes properly 

 Maintain consistent temperatures to avoid pH 

changes 

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Acidification Procedures 

1. Acid blanch food 

2. Immerse blanched foods in acid solution 

3. Direct batch acidification 

4. Add acid foods to low-acid foods 

5. Direct acidification of food in container 

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Acidification Procedures 

 Each acidification method requires proper 

control 

 May utilize more than one procedure 

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Acidification Procedures 

1. Every container of product is acidified in 

same proportions 

2. Monitor acidification by pH measurement 

a) Reference 431.5(e) 

3. Monitor scheduled thermal process 

4. Control container handling 

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Mild heat required, since spores are inhibited by acid. 

Bacteria 

(Vegetative Cell) 

Acid 

c - _: ....e 

Bacteria fi 

(with spore) ~ 

High heat required in order to destroy spores. 

Mild Heat High Heat 

Peas 

Asparagus 

Spinach 

Fish 

Corn 

Meat 

Green Beans 

Beets 

Carrots 

Sweet Potatoes 

Berries 

pH 3.0 

Tomatoes 

Apricots 

Pears 

Pineapple 

Cherries 

Plums 

Sauerkraut 

pH 4.6 

High Acid Foods 

pH 7.0 

Low Acid Foods 

High Acid vs. Low Acid Foods 

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Regulations Governing Acidified Foods 

 USDA - 9 CFR, Part 431 

 FDA - 21 CFR, Part 114, Part 110, and Part 

108.25 

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Failure to Properly Acidify Product 

 If pH is greater than 4.6, then one of the 

following must occur: 

• fully reprocess product 

• process as low-acid food 

• hold for evaluation 

• destroy 

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Record Requirements 

 Maintain records showing adherence to 

processes schedules 

 Retain records of all process deviations 

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Key Points 

 The term pH is used to designate the degree or 

intensity of acidity 

 pH can be determined electronically with a meter or 

by other approved methods 

 It is extremely important to ensure the pH meter is 

correctly maintained, calibrated, and operated 

 Proper acidification of a low-acid ingredient should be 

addressed in the establishment’s HACCP Plan 

 Thermal processes must be designed to destroy all 

vegetative microoganisms 

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Acidified, Low Acid Foods 

 Students should read: 

• 431.1 Definitions: 

• Acidified Low Acid Product 

• Low Acid Product 

• 431.5(e) Measurement of pH 

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Questions? 

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Questions?

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