Acid & Acidified Foods
Acidiﬁed or “pickled” foods are popular food products among food entrepreneurs and farmers interested in value-added opportunities.
Many products are traditionally processed this way, including pickles (cucumbers) and pickled vegetables, meat and eggs. The variety of products and ﬂavors is limited only by the creativity of food processors as new formulations and presentations continuously debut in food stores to meet consumers' new expectations and preferences.
The information contained in this section of this website was prepared by the Cornell Food Venture Center (CFVC) and funded by the United States Department of Agriculture - National Institute of Food and Agriculture (USDA-NIFA) Grant # 2009-51110-20147 and the Cornell University College of Agriculture and Life Sciences.
It is important to understand the regulatory meaning of an acidiﬁed food. From the regulatory point of view, foods are classed as acid, low acid or acidiﬁed depending on the natural acidity of each product. A product’s acidity is measured based on a pH scale. If the raw or initial product has a pH above 4.6 it is considered a low acid food. If the pH is below 4.6 then the food is classiﬁed as an acid food.Acidiﬁed foods are low acid foods to which acid or acid ingredients are added to produce a ﬁnal equilibrium pH of 4.6 or below. Equilibrium pH means the ﬁnal pH measured in the acidiﬁed food after all the components of the food have achieved the same acidity.
The pH value of 4.6 is important because it is the limiting factor for the growth of an extremely dangerous microorganism called Clostridium botulinum, which produces a potent toxin that causes the lethal disease botulism. The regulations concerning acidiﬁed foods were established to assure the control and inhibition of the growth of Clostridium botulinum by proper acidiﬁcation and pH control, as this microorganism is very heat resistant and therefore it is not destroyed by pasteurization or cooking temperatures below 212°F.
We all relate to the word pickled as a food item being treated with an acid liquid, typically vinegar or lemon/lime juice. In doing this procedure we extend the shelf-life of the product due to the preservative effect of the acid as well as develop or produce a sour or pickled taste in the product. In a way, we are imitating a traditional fermentation process by directly adding the acid component to the product. Any food grade acid can be used such as vinegar (acetic acid), citric acid, lactic acid, malic acid or phosphoric acid.
If you are seriously interested in making acidiﬁed foods, you must become familiar with the acidiﬁed foods regulations described in the Code of Federal Regulation Title 21 Part 114 for FDA regulated products and Title 9 Parts 318 and 381 for USDA regulated products. It is also important to review the FDA guidelines for inspection of acidiﬁed foods manufacturers available at FDAs website. In addition, any food manufacturer must obey the Good Manufacturing Practices regulations described in Title 21 Part 117. All documents are available through CFVC for your convenience.
Strictly speaking, the regulations only cover acidiﬁed foods that are shelf-stable, that is, foods that are sold without refrigeration in sealed containers. In reality, any food processor that manufactures acidiﬁed or acid foods, refrigerated or not, should follow the safety factors explained in the FDA and USDA regulations.ion. 2000.
Prior to starting the production of acidiﬁed foods, the processor must register the establishment or processing facility with FDA. The speciﬁc products and procedures used to manufacture the ﬁnal products, called “schedule processes” must also be ﬁled with FDA. In addition, the processor must complete a training program called the “Better Process Control School” or equivalent before engaging in commercial production. This program is offered annually in May by Cornell University and at different dates by other schools. Most likely the processor will need the assistance of a “Process Authority” to develop or verify the schedule process and to help with the ﬁling and documentation requirements. CFVC has several Process Authorities that will work with you during this stage.
Acidiﬁed foods must be properly acidiﬁed to a pH below 4.6, but in practice this value is usually 4.2 or below for safety reasons. The regulations also require a thermal process or heating step to kill all the pathogens and any other spoilage microorganisms that could grow during the shelf-life of the product. To assure quick and proper acidiﬁcation, the food is normally cooked or heated with the acid before being ﬁlled into the ﬁnal container. The pH is checked, controlled and documented prior to ﬁlling and closing. The heating or pasteurization step or process must be done either by hot-ﬁlling the product or by the boiling water bath process. The heating temperature and time are critical factors that must be monitored, controlled and documented. The ﬁnal equilibrium pH is checked and documented after the product has received the heating step. Any other critical safety factors must be monitored, checked and documented as speciﬁed by the schedule process.
To measure the pH, the processor must use a pH meter with two decimal places accuracy if the ﬁnal pH is 4.0 or above. A pH meter is the best method to measure pH and it is recommended for all products and values. If the pH is below 4.0, other methods can be used such as pH paper or a pH meter with one decimal place.
Containers for acidiﬁed foods should be such that a hermetic seal is obtained. The best containers are cans and glass jars/bottles with metal caps lined with a compound called plastisol. With these closures, a good vacuum is obtained. Vacuum is a good indicator of a hermetic seal and helps to keep the quality of the product.
References: Code of Federal Regulations. Title 21 part 114. Ofﬁce of the Federal Register, National Archives and Records Administrat