Selection Guide: Dry Heat vs Steam Sterilization Ovens

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One of the most common roles of a lab oven is to help with sterilization needs. Sterilization is an integral part of the process of developing an evaluative experiment, preparing your samples and the culture media. All forms of life and biological agents need to be eliminated, or at least completely deactivated. That said, sterilization needs to be done quickly, but most importantly, effectively.

Sterilization Through Heat

While there are many ways through which sterility can be achieved, as far as lab ovens go, it is done either via dry heat or steam. In both cases, it is the elevated temperatures that kill all microorganisms, but the key difference in the methods is the existence or absence of moisture.

  • In dry heat, the lab oven is heating up electrical coils and then through air circulated supported by fans, the hot air enters the chamber that hosts the sample and heats it to the set temperature and for a pre-determined period of time.
  • Steam heating works by injecting pressurized hot steam right on the sample, while the air is removed from the chamber. The process continues for a specified period of time, with the pressure inside the chamber remaining stable even after the completion.

Despatch’s LCC Clean Process Benchtop Oven

The Dry Heat Process

Dry heat is usually set to last for at least two hours, letting the sample reach a temperature of 160 Celsius (320 OF). If the sample allows for it, the process can be hastened with a corresponding rise on the temperature, going up to 190 OC (374 OF) for 6 minutes, or even a rapid 30-second heat up to 200 OC (392 OF).

Dry heat causes the organic elements to be dehydrated and gradually burned, so all living organisms die via oxidation. Some bacteria that are particularly resistant to moist heat will be destroyed or irreversibly deactivated when exposed to adequately intense dry heating.

Pros and Cons of Dry Heat

Advantages:

  • Dry heat can effectively kill all organisms that steam heat can’t, like some types of prions that are resistant to moist heating.
  • Powders, metals, and oils should not be heated by steam as that could destroy, alter, or erode them. This leaves dry heat as the only sterilization option for such material.
  • Dry heat ovens are less expensive to buy and less complicated, so they are cheaper to maintain as well.

Disadvantages:

  • Sterilization cycles take a longer time to complete and usually require higher temperatures. This translates to economic burdens as dry heating consumes more energy for extended periods.
  • Flammable materials could combust, and heat-sensitive items could be destroyed by dry heat.

The Steam Heat Process

Steam heating takes place in pressurized autoclave, injecting steam at a temperature of 121–134 °C (250–273 °F) for 3 to 15 minutes, at 103-110 kPa (15-16 PSI). The amount of time required depends on the bio-burden of the sample, but it is generally much quicker than dry heat.

Steam can cause damage to the sample, so depending on its type, it may not be applicable. During the steam heating process, the proteins in the living organisms are getting coagulated, and thus all bacteria, spores, and fungi die.

Pros and Cons of Steam Heat

Advantages:

  • Steam heating cycles only require a few minutes to complete, so they cost less to carry out and help with lab productivity in the long term.
  • Liquids and flammable material can only be sterilized via the moist heating of steam.
  • Can penetrate dense samples, wrapped items, containers, tubes, and other hard to reach places.

Disadvantages:

  • Some prions, bacteria, and mold spores are resistant to moist heating, and no matter how high the temperature will go, complete sterility will not be achieved.
  • Steam should be used on materials that cannot tolerate moisture such as powders, anhydrous fats, oils, and metals that are not corrosion resistant and/or can rust.
  • Steam heaters require pressure vessels, nozzles, pits, exterior jackets, etc. Thus, they cost quite a lot to acquire as well as to maintain.

Remember, whether it’s dry heat or steam sterilization ovens that you prefer or need, Despatch has you covered with a wide range of products on both categories. Reach out to our experts to get a specially crafted quote today.

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