Preserving Acidified Foods Using the Hot-Fill-Hold Process

Circular 1328-03

This publication is part of the Acidified Foods series.

For questions about this or other food science topics, please contact Extension Food Science at efs@uga.edu or call 706-542-2574.

Typical Times and Temperatures Used in Hot-Fill-Hold

The hot-fill-hold (HFH) process involves heating the product to around 180–200 °F, then filling, inverting, and holding for 2–5 min to achieve commercial sterility. Higher temperatures will generally correlate with shorter hold times, and lower temperatures will generally correlate with longer hold times.

When measuring the hold time and temperature, it is important to consider the cooling that takes place during the hold period. Generally, the hold temperature will be specified as the last (or lowest) product temperature recorded during the hold period.

Tools and Equipment Needed

access to a licensed manufacturing facility
calibrated digital thermometer
calibrated digital pH meter
digital timer
heating equipment
spatulas, ladles, etc.
heat-stable containers with lids
food ingredients
lab notebook or other place for recordkeeping

Products Suitable for HFH

Products must be naturally acidic or must be acidified to maintain the equilibrium pH at 4.6 or below. Products processed using HFH generally need to be able to flow—such as sauces, beverages, or salsas—to ensure contact with the container.

This process is not suitable for products that cannot flow readily or do not contain enough acid to maintain an equilibrium pH of 4.6 or below, which will inhibit the growth of Clostridium botulinum and cause it to remain in a sporulated state. In its vegetative state, it will produce a toxin that causes paralysis and death, but in its spore form, C. botulinum will not be harmful to human health.

A product with a pH of 4.6 or above will require a more severe thermal process, under pressure, of 240–260 °F for a processing time of several minutes up to an hour or more. The target microorganisms that producers want to deactivate using the HFH process include vegetative pathogens such as Salmonella, E. coli, and Listeria, as well as spoilage bacteria, yeast, and mold.

Steps to Process Using HFH

Refer to Figure 1 for a visual guide to the HFH process and read the steps below for additional information.

a flow chart listing the steps of the hot fill hold process with details — Figure 1. Steps in the Hot-Fill-Hold Process.

Product Formulation
The formulation of the product should be determined ahead of time in collaboration with a process authority. The process authority will classify the product as acid, acidified, or low acid. If the product does not meet specifications to be an acid or acidified product, either based on the acidification process or the equilibrium pH, then the product will need to be reformulated or use a process other than HFH.
Product Preparation
The product is prepared according to the recipe, following good manufacturing practices (often called GMP). If the product is not naturally acidic, this preparation should include steps to acidify the product and reduce low-acid ingredients to a pH of 4.6. Product preparation may include chopping, grinding, blending, roasting, etc., and—for the HFH process—must form a homogenous, flowable product.
Heating
The prepared product is heated to a temperature specified by a thermal process authority. The temperature used will range from 180–200 °F prior to filling, depending on the type of product. Heating will inactivate vegetative pathogens and spoilage organisms and may also destroy enzymes that can spoil a food during its shelf life. Sufficient heating also ensures that a hermetic seal will form by softening and molding the sealing compound around the lip of the container.
Filling
The product needs to reach the desired initial fill temperature. A process authority will generally recommend a minimum initial fill temperature above what is needed to achieve sterility, especially if the process tends to be variable. Once the specified initial temperature is reached, the containers can be filled.
Holding
The containers must be held at a specified minimum temperature for a minimum amount of time, as determined in consultation with a process authority. Sometimes the hold temperature is not the minimum initial temperature because the product will cool over time. Instead, readings should be taken regularly over a period of several minutes, and the lowest temperature reached at the end of the hold time can be used as the hold temperature.

Alternatively, a water bath or water spray can be used to maintain the containers at a specified temperature over the hold time. The time typically will be in the range of a minute to several minutes, and will include an inversion of the container that lasts several seconds up to a couple of minutes to sterilize the headspace and properly form a hermetic seal.

The rate at which the container cools depends on the container size, the consistency of the product, and the air temperature of the production facility. The hold time and temperatures are determined as the minimum requirements to destroy microorganisms of public health concern, assist in sealing the container properly, and inactivate enzymes that can degrade the product.
Cooling
After holding, the containers will be cooled as quickly as possible to maintain product quality. Overcooking can degrade ingredients in a product. Containers can be cooled to room temperature with air or water. Sufficient cooling will also aid in container handling, labeling, and packaging.
Verification of pH
Measure the pH once the product reaches room temperature (within 24 hr) to ensure the equilibrium pH is 4.6 or below. If there are both solid and liquid components, be sure to measure both components.

If the product is not acidified within 24 hr, the product must be re-acidified and reprocessed, processed using an alternative process suitable for low-acid foods, or disposed of. A process authority can be contacted to determine product disposition.

海角官方首页