Throughout our experience in food biotechnology, we’ve encountered many challenges related to food preservation. One recurring issue is identifying products that, due to their specific characteristics, are not suitable for autoclave sterilization.
You’ve likely come across situations where the results of thermal processing were not as expected—whether due to changes in texture, flavor, or even concerns around food safety.
In this article, we’ll explain which foods are not compatible with autoclave sterilization and why, so you can make more informed decisions in your preservation processes.
Why are some foods incompatible with autoclave sterilization?
There are three main reasons why certain foods don’t respond well to autoclaving: microbiological, chemical, and technological factors. Let’s break these down.
Microbiological reasons
Autoclaving is an effective method for eliminating heat-resistant bacteria and spores, such as those from the Clostridium genus.
However, not all foods require such intense thermal treatment. Some, thanks to their natural properties, can remain microbiologically safe without needing to be sterilized in an autoclave—provided they’re formulated, packaged, and stored correctly.
For example, we once worked with a customer who wanted to sterilize nuts. This kind of product, like highly sugared jams or pickled foods with low pH, often has natural microbial stability in certain conditions.
In such cases, using an autoclave may be an unnecessary use of time and resources. Still, it’s always essential to assess each product individually before skipping sterilization.
Chemical reasons
The intense heat used in autoclaves can alter the nutritional properties of some foods or even trigger the formation of undesirable compounds.
Take vitamin C, for instance—it’s abundant in citrus fruits and bell peppers but degrades quickly under high temperatures. Similarly, in dairy or protein-based beverages, Maillard reactions (responsible for browning) can reduce nutritional quality and negatively affect the flavor and appearance of the final product.
Technological reasons
Product texture and packaging material play a critical role in determining whether a food item can withstand autoclave sterilization.
In one case, we worked with delicate vegetables like spinach and berries, which didn’t tolerate the process well. The combination of heat and pressure severely damaged their structure and appearance.
We’ve also seen plastic containers that weren’t heat-resistant melt during the cycle. These situations highlight the importance of technically evaluating both the product and its packaging beforehand.
How to easily identify incompatible foods
When advising companies, we always recommend a quick three-step approach to verify whether a product is suitable for autoclaving:
- Measure pH and water activity (aw): If both values are low, pasteurization is often sufficient to ensure safety.
- Run pilot tests: Small-scale thermal trials help detect potential issues before committing to full-scale production.
- Test packaging under real autoclave conditions: This helps prevent warping, leakage, or contamination from unsuitable materials.
Common mistakes to avoid
Here are some frequent errors we’ve encountered in food preservation projects:
- Applying autoclave sterilization to foods that already have natural microbial stability.
- Overlooking the degradation of key nutrients caused by high temperatures.
- Using containers that aren’t designed to withstand thermal and pressure conditions.
Examples of foods that don’t work well in autoclaves
To make identification even easier, here are some typical examples of foods that present challenges during autoclave sterilization, due to their composition or thermal behavior:
Very fatty foods (oils, butters, animal fats)
High fat content acts as a heat barrier, making it harder to destroy bacterial spores. In these environments, Clostridium botulinum can potentially survive, posing a serious health risk.
Alternative: Cold storage, dehydration, or acidification.
Dairy products
Milk and dairy derivatives—especially those rich in proteins and fats—often separate, coagulate, or suffer severe changes in taste and texture. Some cheeses may lose their structure or release whey.
Outcome: Loss of quality and consumer rejection.
Raw egg-based products (mayonnaise, egg creams)
Heat causes proteins to coagulate and phases to separate, leading to major texture changes.
Result: Sensory issues and product instability.
Foods high in sugar (highly concentrated jams, confectionery)
At high temperatures, sugars can caramelize or degrade, affecting both color and flavor.
Consequence: Loss of desired organoleptic properties. See our dedicated guide on jam sterilization for more details.
Alcohol-containing products (preserves with liquor, wine, or spirits)
Alcohol has a low boiling point and can evaporate quickly during autoclaving, leading to internal pressure buildup, deformed packaging, or even leakage.
Recommendation: Use gentle pasteurization or preserve through direct alcohol incorporation.
Cooked rice or pasta
These ingredients absorb even more water during sterilization, leading to overcooking.
Solution: Controlled cooking inside the final container or milder heat treatments.
Probiotic or live yeast products
Autoclaving kills all microbial life—including beneficial microorganisms.
Recommendation: Add probiotics after thermal processing, as is done in some commercial yogurts.
What if autoclaving isn’t the best option?
Don’t worry—there are effective alternatives:
- Pasteurization: A milder heat treatment suitable for foods with low pH or reduced water activity.
- UHT processing: Ideal for liquids requiring rapid sterilization without major quality loss.
- Emerging technologies: High-pressure processing (HPP) or pulsed electric fields preserve nutritional and sensory quality more effectively.
Practical tips that work
One key recommendation: train your team to quickly identify incompatibilities. In addition:
- Establish clear protocols, especially during product design and quality control stages.
- Regularly monitor thermal cycles and packaging condition.
- Choose packaging materials carefully, keeping both the product and the process in mind.
These best practices help avoid costly issues and ensure consistent results.
If you ignore these incompatibilities you could face serious food safety risks, economic losses, or damage to your company’s reputation.
The bottom line: Know your food
In conclusion, understanding your products in depth—and the reasons they may or may not be compatible with autoclave sterilization—is crucial.
The best way to ensure safe, nutritious, and high-quality food is to choose the right method and follow sound practices.
We hope our experience helps you avoid common mistakes and improve your food preservation processes.
Would you like to know which foods can be autoclaved? Find out in our blog article.
References
Cho, W. I., & Chung, M. S. (2020). Bacillus spores: a review of their properties and inactivation processing technologies. Food Science and Biotechnology, 29, 1447-1461. https://doi.org/10.1007/s10068-020-00809-4
Takeda, Y., Shimada, M., Ushida, Y., Saito, H., Iwamoto, H., & Okawa, T. (2015). Effects of Sterilization Process on the Physicochemical and Nutritional Properties of Liquid Enteral Formula. Food Science and Technology Research, 21(4), 573-581. https://doi.org/10.3136/fstr.21.573
Valencia-Flores, D. C., et al. (2021). Thermal Processing of Foods: Fundamentals, Food Chemistry, and Food Processing. Encyclopedia. https://encyclopedia.pub/entry/15517
Mieszczakowska-Frąc, M., Celejewska, K., & Płocharski, W. (2021). Impact of Innovative Technologies on the Content of Vitamin C and Its Bioavailability from Processed Fruit and Vegetable Products. Antioxidants, 10(1), 54. https://doi.org/10.3390/antiox10010054
Jimenez, P. S., Bangar, S. P., Suffern, M., & Whiteside, W. S. (2024). Understanding retort processing: A review. Food Science & Nutrition, 12(3), 1545-1563. https://doi.org/10.1002/fsn3.3912
