Choosing a gelling agent depends on your needs for your in vitro culture medium. Factors to consider when deciding are transparency, level of impurities, melting and gelling temperature, gel strength, and cost.

A gelling agent or solidifier is used to prepare semi-solid tissue culture media.

In culture media, gelling agents provide plants or bacteria physical support, aeration, and favor the growth.

Common gelling agents include agar, phytagel, xhantam gum, carrageenan, isubgol, and guar gum.

Of course, the question becomes, what gelling agent is right for my experiment?

First, we recommend you don't rush the decision to choose because gelling agents may affect the growth and behavior of the evaluated tissues.

Instead, you'll need to take some time to consider the needs of your cell culture and your experiment to choose the right gelling agent.

We will highlight the most critical things to consider when deciding which gelling agent to use and provide tips on choosing a gelling agent.

Clarity or transparency:

Clarity is how transparent your solid media looks. For instance, phytagel is clearer than agar. A transparent solid media favors contamination identification during plant tissue culture.

A clearer gelling agent such as GelRite is more expensive than a non-clear gelling agent (e.g., agar) because the former is refined and is commonly extracted from bacteria growth industrially.

  • Tip: If the purpose is to detect contamination in plant tissue culture, we recommend you use a gelling agent such as GelRite to obtain a transparent medium. Agar can be used if you want to promote bacterial growth or when using it as plant support.

Level of impurities:

Impurities like phenolic compounds are toxic to specific organisms. Because agar is derived from natural algae, it commonly has more impurities.

Therefore, agar has higher impurities than bacterial-based gelling agents such as GelRite.

The level of impurities in the agar has been associated with in vitro plants and bacteria variability.

  • Tip: If the work is routine for bacterial and plant growth, agar can be ideally used. If the work is focused on research (where tissue behavior is evaluated), gelling agents like GelRite with low impurities are preferred. The good news is both agar and GelRite are easy to use.

Melting temperature:

Each gelling agent has a specific melting temperature that, if reached, the media is no longer solid.

In this sense, some gelling agents favor the growth of extreme microorganisms or extremophiles (some require high temperature to grow) and maintain the media solid.

Below there is a table with the melting temperatures for gelling agents organized from the lowest to the highest melting temperatures.

Gelling agent

Melting temperature




Between 50°- 80°C

Gellam gum (GelRite)



> 100°C

Xanthan gum


  • Tip: To choose the appropriate gelling agent for your experiment, check the temperature requirements to grow your organism and select the gelling agent that melts above 5-10 °C at the growth temperature.

Gelling temperature:

Gelling temperature is the temperature where the gelling agent solidifies the media.

This parameter matters for gelling agents because you may need more or less heat to keep melted your gelling agent while pouring plates before it solidifies.

The gelling temperature for agar is around 37°C and for GelRite is about 65°C. The melting temperature can vary slightly depending on the manufacturer.

  • Tip: Keep the media temperature at least 5-10°C above the gelling temperature to avoid the media solidifying before you pour plates. In any case, revise the manufacturer's recommendations.
  • Tip:Revise the scientific literature regarding your studied organism/tissue. Previous reports can give you an idea of which gelling agent to start with. Also, revise your study goal. It will help you to decide if you need more or less gel strength.

Gel strength:

Gel strength refers to the force needed to break the gel.

Examples of gelling agents with high, medium, and low gel strength are agar (>1100 g/cm2), carrageenan (100 to 1200 g/cm2), and GelRite (400 - 700 g/cm2).

Gelling agent

Gel strength


Gellam gum (GelRite)

400 - 700 g/cm2



100 to 1200 g/cm2



>1100 g/cm2


The gel strength is relevant depending on the goal for solid media. For instance, a higher gel strength favors the root development for in vitro plant culture.

Low-middle gel strength is preferred for experiments where a semi-solid media is needed. For instance, plants with weak root systems grow well in semi-solid media.


As with anything, some gelling agents will be more cost-effective than others.

One of the reasons for the cost difference is the origin and cost of production.

For instance, GelRite costs less than agar because it is derived from bacterial fermentation, a process more industrialized. As agar comes from seaweed, this plant material is getting scarce and makes the agar more expensive.

  • Tip:You may select seaweed or bacterial-derived gelling agents according to your budget and research goals. At GoldBio, we offer high quality and good prices for gelling agents to help you advance your research. We offer plant agar, micro agar, phyto agar and GelRite.

Metabolically inert or active:

Some gelling agents react with cations to form 3D structure networks.

For instance, if you use GelRite or phytagel, you should include cations in the media, such as calcium or magnesium for solidification. Otherwise, you will not get solid media.

Agar does not require cations to solidify; thus, the medium can be cation free.

* Tip:If you need to prepare a solid medium, include cations like calcium or magnesium (usually in the form of salts) when using GelRite. You may not need this type of cation to obtain solid media if you use agar. In any case, review the manufacturer's guide.

Printable guide for choosing your gelling agent

We have provided a helpful printable sheet to guide you through the decision process of finding the right gelling agent for your culture media.

The printable sheet provides you questions and calls to actions to help you choose which is best for you.

how to choose a gelling agent decision guide chart picture for download

For instance, if you need a gelling agent free of impurities, this guide will show you options. However, it will also point to important considerations, such as what to do if your gelling agent is metabolically active.

Or if you need a gelling agent low in impurities (bacteria-based) but with a higher gel strength, you will find options on the chart as well as guidance on how to get a higher gel strength by altering the concentration.

list of considerations for choosing a gelling agent


Gelling agents, considerations, tips.


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