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Food Safety Considerations in the Production of Traditional Fermented Products: A Review Article

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By Laurie Post, Ph.D.
A recent article in the Journal of Food Safety by authors at the Federation University in Australia reviewed the processes used in the production of Japanese rice koji and miso and developed a hazard assessment for these fermented foods.

Miso is a traditional fermented soybean paste made for thousands of years. The most common type of miso is made from rice koji, salt, and soybeans using a two stage fermentation process. The first step is the production of koji where rice is fermented with a mold such as Aspergillus oryzae at 30°C for 48 h. The koji and salt are then added to boiled soybeans and fermented by yeasts and bacteria for 2 to 24 months. Koji and miso are increasing in popularity in western countries where contemporary miso varieties are not pasteurized as consumer demand is for more natural products containing live microorganisms. While correctly prepared fermented foods are rarely associated with foodborne illness outbreaks, there have been several reports of illness. These were primarily due to pathogenic microorganisms introduced into the products from external sources such as raw materials or the processing environment. Hygiene and fermentation conditions must be carefully monitored to ensure food safety.


The authors point out that many of the production steps in the manufacture of koji and miso do not fit into contemporary food safety guidelines. Although a reduction in pH is a typical food safety hurdle for fermented foods, this does not apply to non-acidic foods such as koji or miso. Use of a certified safe mold as the starter culture and monitoring appropriate temperatures to ensure prolific growth of the mold (and to minimize growth of unwanted bacteria) are requirements for the safe production of rice koji. An optimized salt content and reduced water activity (Aw) is a food safety hurdle in the production of miso. Focusing on the quality of ingredients and hygienic practices along with the development of standardized
fermentation conditions, would also assist in safe production of these fermented foods. The authors conclude that research on unpasteurized koji and miso is needed to determine optimized temperatures, pH and Aw levels, and salt concentrations during the fermentation process that would assure these fermented foods comply with food safety requirements.

Recent Outbreaks Involving Natural Toxins

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By Ryan Maus
Ingredient hazard assessments often include an assessment of natural toxins. Of these, mycotoxins such as aflatoxin are often first to be assessed. However, other naturally occurring toxins exist and have caused foodborne outbreaks in the past few years. These outbreaks involved toxin containing raw morel mushrooms, undercooked kidney beans, and new ingredients such as tara powder. While consumer
demands can inspire new food trends, it is important to remember the hazard that naturally occurring toxins present and the controls that can
be put in place to reduce the risk of illness.

A recent article describes a 2018 incident in France where an outbreak of acute gastroenteritis occurred at a military base after 200 people ate at a dining facility and became ill. An investigation indicated that chili con carne was the likely source of illnesses. Further analysis indicated that a plant lectin, phytohaemagglutinin, was present in the chili at a level above what is considered a toxic dose. The source of the plant lectin was undercooked kidney beans, a toxin that is destroyed with proper cooking of the beans.


In 2022, numerous customer complaints were made to the manufacturer, the FDA, and the CFSAN Adverse Event Reporting System about illnesses associated with the consumption of Daily Harvest’s French Lentil and Leek Crumbles. The product was eventually recalled and an outbreak investigation undertaken to determine the cause of illnesses. Initially, 393 adverse illness events were reported, including 133 hospitalizations. Illnesses reported involved the gastrointestinal tract, liver, bile ducts, and/or gallbladder. An FDA investigation identified tara protein flour, an ingredient in the product implicated, as an ingredient of interest although non-specific toxin tests, mycotoxin tests, and microbial tests did not identify any results of public health significance. An investigation of the adverse event and the potential role tara protein played in causing illness was published in 2023. The authors found that the original product and tara protein powder ingredient were free from intentional, accidental, and economic adulteration, spiking with synthetics, and toxic compounds. However, three nonprotein amino acids were present at high levels. One of these, baikiain, was present at the highest level and produced a minor metabolite in vivo similar to acetaminophen. When tested using a mouse model at levels relative to consumer consumption, the mice exhibited liver and kidney symptoms similar to an overdose of acetaminophen. The presence of baikiain was theorized to have caused the adverse events seen in consumers, the severity of which depended on the dose of tara consumed and the susceptibility of the individual to the toxin.

In 2023, an outbreak at a sushi restaurant in Montana caused 51 illnesses involving diarrhea, nausea, vomiting, or abdominal pain; and two deaths. An investigation indicated that morel mushrooms were the likely cause of illness. Left over mushrooms tested were found to be true morels and not false morels that contain the toxin gyromitrin, and no significant levels of pesticides, heavy metals, toxins, or pathogens were found. However, documented cases of similar illnesses associated with consumption of raw or undercooked true morel mushrooms have been reported due to low levels of naturally occurring heatlabile hydrazinic toxins in the raw morels. Morels consumed at the restaurant were served raw or lightly cooked.

Food producers need to ensure that proper controls are in place to eliminate toxic hazards, such as cooking. Likewise, new ingredients incorporated into products should be FDA approved and have a history of being safe. More information on natural toxins is available from FDA, WHO, and other sources.

Current Recall a Reminder of Past Incident Involving Frozen Vegetables Contaminated with Listeria monocytogenes

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A new recall of frozen vegetables was published on August 23, 2023, due to the finding of Listeria monocytogenes in sweet cut corn. Recalled products were distributed to major retailers across the U.S. having best by dates as far away as December 2024. Listeria monocytogenes, like many pathogens, will not be eliminated by freezing and will persist in the frozen product. While little information is given in the recall, findings from a 2016 listeriosis outbreak involving frozen vegetables is highlighted in the following.


In 2016, the first multistate outbreak of L. monocytogenes involving frozen vegetables occurred in the U.S. Initially three persons reported illness in 2016, but six more illnesses occurring between 2013 – 2015 were identified using PulseNet traceback data. Two outbreak strains were identified in patients ranging in age from 56 to 91 years and three deaths were reported.


Routine sample of frozen vegetables, and the use of whole genome sequencing (WGS), revealed that eight illnesses were closely related to a strain found in frozen organic white sweet cut corn and one illness to a strain found in frozen organic petite green peas produced by CRF Frozen Foods of Pasco, WA. At the same time, an investigation of the Oregon Potato Company of Pasco, WA found that environmental samples matched the whole genome sequence associated with the eight clinical cases and the CRF frozen organic white sweet cut corn. However, a connection between the companies is unknown because the FDA is prohibited by law from releasing publicly certain information about supply chains, which may constitute confidential commercial information.


A recent publication describes the investigational findings by federal and state regulatory agencies at the two frozen vegetable manufacturers. Observations at the CRF Frozen Foods’ facility indicated that the materials and design of equipment and utensils did not allow proper cleaning and maintenance, and could be potential sources of contamination. An investigation of the facility did not find L. monocytogenes in the environment, but L. innocua was found in zones 1 – 3 which FDA considers evidence of conditions that would be suitable for L. monocytogenes.


Seven L. monocytogenes positive zone 1 swabs, two positive zone 2 swabs, ten positive zone 3 were found in the Oregon Potato Company’s facility. Two of these positives, one zone 1 swab and one zone 3 swab,- matched an outbreak strain also found in CRF’s frozen organic white sweet cut corn. Inspectional observations made include:

  • failure to clean food‐contact surfaces as frequently as necessary to protect against contamination
  • facility construction that did not prevent condensate from contaminating food‐contact surfaces
  • food‐contact surfaces not adequately cleaned and sanitized
  • failure to maintain physical facilities in a sanitary condition
  • facility construction not allowing adequate cleaning of floors and walls

A FDA warning letter was issued and noted the presence of L. monocytogenes in the facility as being indicative of inadequate sanitation efforts to effectively control pathogens in the facility. Although these products are considered not ready‐to‐eat, many consumers may use these products
without proper cooking. Cooking instructions should be clear and validated, and consumers should be informed that consuming undercooked or uncooked frozen vegetables could lead to foodborne illness.

A Recent Soft Serve Ice Cream Outbreak and a Look Back at Past Incidents Involving Pathogen Contamination

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A recent outbreak of listeriosis has been linked to Soft Serve On The Go ice cream cups, resulting in 2 illnesses. An investigation by the Pennsylvania Department of Agriculture detected the presence of Listeria monocytogenes in an unopened sample of ice cream taken from a patient’s home. The product isolate was matched to the clinical L. monocytogenes outbreak strain by whole genome sequencing. Five positive samples of finished product obtained from the production facility by the New York State Department of Agriculture and Markets also matched the outbreak strain.

A recall of products distributed nationally is currently ongoing. However, this is not the first outbreak or recall associated with ice cream and many others have occurred as shown in the tables below.

YearLocationPathogenIllnessesDeathsProducer
2022MultistateL. monocytogenes281Big Olaf Creamery
2014WashingtonL. monocytogenes22Snoqualmie Ice Cream
2010-2015MultistateL. monocytogenes103Blue Bell
2005MultistateSalmonella260Cold Stone Creamery
1994MultistateSalmonellaEstimated 224,0000Schwan’s
Past ice cream outbreaks are shown in the following table.
DatePathogenPathogen SourceProducer
07/13/2022L. monocytogenesEnvironmentBig Olaf Creamery, LLC
06/06/2022SalmonellaPeanut ButterTaharka Brothers Ice Cream
02/12/2022L. monocytogenesEnvironmentThe Royal Ice Cream Company, Inc.
04/27/2021L. monocytogenesNot MentionedVelvet Ice Cream
05/14/2020L. monocytogenesNot MentionedRamar Foods
03/17/2020L. monocytogenesEnvironmentWorking Cow Homemade Ice Cream
Recent ice cream recalls due to pathogen contamination are shown in the following table.

Contamination of ice cream products generally occurs after pasteurization, resulting from sources that include the addition of contaminated inclusions (e.g. fruits, nuts, candy, or bakery pieces) to the finished product, contamination from the production environment, and inadequate sanitation of equipment such as filling heads. Freezing ice cream can prevent pathogen outgrowth, but it will not eliminate pathogen presence. Low levels of pathogens causing illness were identified in the 1994 Schwan’s outbreak (Salmonella 0.004-0.46 MPN/g) and 2015 Blue Bell outbreak (L. monocytogenes 3.9-7.1 MPN/g).

Supplier verification programs are critical to evaluate inclusions and reduce the risk associated with them. Inclusions and flavors must be ready-to-eat and any required Process Preventive Controls must have been applied at the supplier, unless the ice cream manufacturer assumes this responsibility.

Sanitation controls are critical to prevent post pasteurization pathogen contamination of finished ready to-eat ice cream products. This is especially true for L. monocytogenes. Cross contamination with L. monocytogenes from the environment is identified in Blue Bell’s 2015 outbreak and numerous recalls. Ice cream processes can be hard to clean, leaving behind nutrients for microbial growth. Listeria can grow,
form biofilms, and persist in harborage sites such as drains leading to cross contamination. Biofilm formation is a constant problem in ice cream producing facilities and requires proper cleaning and sanitizing procedures for their removal and prevention. The effectiveness of sanitation programs are verified by the results attained from a well-designed environmental monitoring program

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