Can you freeze Agar plates? 

In this brief guide, we’ll explore the query: “Can you freeze Agar plates?” Also, we’ll explore how Agar plates can be stored, what Agar plates are, what are the most commonly used growth mediums made with agar, and what are precautions to take when handling cultures in agar plates. 

Can you freeze agar plates

No, freezing agar plates is not recommended, as the subzero temperatures will freeze agar to a solid block, and once it defrosts, the agar’s structure will be destroyed. 

Agar plates are commonly used in microbiology for applications such as diagnostics, characterizations, and chemical profiling. 

Naturally, the agar plates on which these microbes will be cultivated should be of the highest structural quality, and not be subject to any type of degradation. 

Below, we’ll describe a few procedures and handy tricks for storing agar plates.  

How can I store agar plates

Agar plates are best stored in refrigeration once their surplus humidity has evaporated. Usually, this happens within 3 to 5 days of the agar being cast into the Petri dishes. 

Freshly cast agar plates should not be used for cultivating microbes, as the thin film of water (the surplus humidity) on the agar will spoil the culture’s orderly growth, and jeopardize the undertaken studies. 

Rather, freshly cast agar plates should be left to sit at room temperature with their lids in place and the excess humidity will dry within 3 to 5 days.

After, the agar plates can be carefully placed inside a plastic bag, and refrigerated at 4°C. 

Alternatively, plates that will be used in a culture can be stored at room temperature and then inoculated via isolation techniques for bacteria and fungi.

Agar plates that have been used to grow a culture can be stored in refrigeration to halt the microbe’s growth (for a pause in the studies), while those being actively cultivated and studied can be placed in an incubator at the microbe’s ideal temperature to promote its growth. 

When not in use, Agar plates are best kept refrigerated inside sealed plastic bags to keep out contaminants such as airborne microbes and mites. 

Contaminated and overgrown agar plates should be discarded by heating them in an autoclave and disposing of them following laboratory guidelines.  

If the Petri dishes are made of glass, the agar can be scraped out and the dishes washed, autoclaved, and recycled, whereas plastic Petri dishes can be autoclaved and discarded whole. 

What are agar plates

Agar plates allude to Petri dishes that have been filled with growth media, that is used for the controlled – in vitro- cultivation of microorganisms, such as bacteria and fungi. 

Agar plates can be used by research biologists, diagnostic laboratories, medical personnel, and companies that use microbes to obtain products such as cultures, enzymes, toxins, and other metabolites.  

Agar plates are made by combining the ingredients of the growth medium such as sugars, salts, and other components such as extracts, and then combining them with water inside a flask. 

Once all the growth media’s specific ingredients have been added to the water, the agar can be poured in, and the mixture will be prepared by placing the flask (which has been sealed with a cotton plug and a foil hood) into an autoclave. 

The autoclave’s heat will boil the mixture to the point where all the ingredients will be dissolved and after it has cooled to a temperature that can be held in one’s palm, the plates can be cast using common sterile-lab procedures

After 3 to 5 days, the excess water content will have evaporated from the plates, and they’ll be ready to be used for isolation and cultivating

What are the most commonly used growth mediums made with agar

The growth mediums most commonly used to make agar plates will vary between applications.

For example, medical professionals may use agar plates made with blood to first grow microbes that cause disease, and from that culture, they may isolate microorganisms into other plates that are made with salts, antibiotics, and other nutrient sources. 

Environmental microbiologists may use agar plates made with other components such as PDA, which is made of potato extract, and dextrose (a special type of sugar). 

There are specialized growth mediums used to cultivate specific types of microorganisms, and they may be made with different types of sugars, but a common ingredient in many is agar, which confers a solid state to the growth media.  

What precautions should I take when handling cultures in agar plates

Agar plates should be handled with caution to keep them free of contaminants, and in the case of medical laboratories, to prevent contagion of the personnel handling them. 

Agar plates that are in active growth should be handled as little as possible to avoid temperature changes and to keep them from being exposed to airborne contaminants such as bacteria, molds, and mites. 

Sealing agar plates with parafilm is recommended to prevent the petri dish lids from lifting off and facilitating the entry of contaminants. 

Cultures should be placed in refrigeration to halt microbial growth.  

Preserving microorganisms in agar dishes is only recommended when the microbe can resist desiccation, as is the case with spore-forming microorganisms such as fungi, and some bacterial cultures. 

Microorganisms that don’t survive desiccation but must be preserved, can be transferred to test tubes with previously- cast growth media at the bottom, and preserved with a layer of thrice-autoclaved glacial acetic acid. 

We recommend our readers consult specialized manuals, workbooks, and textbooks to resolve any doubts they have when handling agar-based growth media and cultures. 


In this brief guide, we’ve explored the query: “Can you freeze Agar plates?” Also, we’ll explore how Agar plates can be stored, what Agar plates are, what are the most commonly used growth mediums made with agar, and what are precautions to take when handling cultures in agar plates. 


Hi, I am Charlotte, I love cooking and in my previous life, I was a chef. I bring some of my experience to the recipes on this hub and answer your food questions.