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This page describes products and general use; it is not medical advice.
A candle jar is a sealed jar in which a burning candle consumes oxygen and raises carbon dioxide, so that microorganisms with special atmospheric needs can be cultured. Laboratory staff, buyers and microbiology students use this page to tell a candle jar apart from an anaerobic jar and an anaerobic chamber, and to see how each is classified and how well each works.
What is a candle jar?
A candle jar is a sealed jar holding culture plates and a lit white wax candle. When the candle burns inside the sealed jar, it produces about 4-5 per cent carbon dioxide and lowers the oxygen level at once, but it leaves roughly 1-2 per cent unburnt oxygen (Saha et al., Indian Journal of Medical Research, 2016). That residual oxygen is why a plain candle jar creates a CO2-enriched, reduced-oxygen atmosphere rather than a strictly anaerobic one.
Who uses it: clinical and teaching microbiology laboratories that culture organisms with special atmospheric requirements.
What is an anaerobic jar?
An anaerobic jar is a sealed container in which oxygen is removed so that anaerobic organisms can grow. The same 2016 paper describes the anaerobic jar as the most common way of maintaining an oxygen-free environment for anaerobic culture. Commercial systems of the GasPak type are described there as acceptable for most small-scale laboratories, but single use, costly, and taking more than an hour to reach critically low oxygen levels.
Anaerobic jar uses
The jar holds inoculated plates in a low-oxygen atmosphere during incubation. Commercial gas-generating systems for such jars fall under US federal regulation 21 CFR 866.2580, which defines a gas-generating device as a device intended for medical purposes that produce predetermined amounts of selected gases for use in a closed chamber, to establish suitable atmospheric conditions for cultivating microorganisms with special atmospheric requirements; the regulation states that such a device aids in the diagnosis of disease. It is classified as Class I (general controls) and is exempt from premarket notification, subject to the limitations in 866.9. For how premarket notification works for other devices, see our guide to FDA 510(k) premarket notification.
What is an anaerobic chamber?
An anaerobic chamber is a glove box configured to exclude oxygen, so plates and cultures can be handled and incubated without leaving the oxygen-free space. The 2016 paper lists the anaerobic glove box technique among the methods used in some sophisticated laboratories. For the enclosure itself, see our guide to what a glove box is. The principle differs from a jar: a jar creates its atmosphere inside a small sealed container, while a chamber is a working enclosure.
How the methylene blue indicator shows anaerobiosis
A methylene blue indicator is placed in the jar as a visual check on anaerobiosis. In the 2016 study the methylene blue strip stayed colourless until the jar was opened, which was the expected result in an anaerobic jar.
Types and variants
| Type | How the atmosphere is made | Key difference |
|---|---|---|
| Candle jar | A white wax candle burns in the sealed jar, giving 4-5 per cent CO2 | About 1-2 per cent oxygen is left unburnt |
| Modified candle jar | Candle plus steel wool treated with acidified copper sulphate | The treated steel wool absorbs the remaining oxygen after the candle burns |
| Commercial anaerobic jar (GasPak type) | Gas-generating system in a sealed jar | Single use and costly; more than an hour to reach critically low oxygen |
| Anaerobic chamber (glove box) | Enclosure configured to exclude oxygen | A working enclosure, used in some sophisticated laboratories |
Table sources: Saha et al., 2016. The glove-box row also matches our glove box guide.
What the evidence shows on performance
In a comparison on 150 deep-seated abscess samples, a two-step modified candle-jar system and the Anoxomat system recovered 26 anaerobes. Growth degree and colony size were similar in both systems, except for Clostridium difficile (Saha et al., 2016). This is one laboratory’s study, not a general rule for every jar.
How the systems differ in practice
The sources compare the systems on three points: how quickly low oxygen is reached, whether the system is single use, and whether oxygen is left over. Manufacturer instructions for use and each laboratory’s own protocol govern everything else.
Safe use and handling basics
Follow the product’s instructions for use and your laboratory’s biosafety procedures. For general technique, see aseptic technique and culturing microorganisms.
Common mistakes
- Treating a plain candle jar as strictly anaerobic, when roughly 1-2 per cent oxygen remains.
- Assuming a commercial jar reaches low oxygen immediately; the source reports more than an hour.
- Overlooking the indicator; a colourless methylene blue strip was the expected result in the study.
FAQ
What is an anaerobic jar?
A sealed jar in which oxygen is removed so anaerobic organisms can be cultured; it is the most common method for oxygen-free culture.
What is an anaerobic chamber?
A glove box configured to exclude oxygen, used in some sophisticated laboratories. See what a glove box is.
What is a candle jar?
A sealed jar in which a burning white wax candle produces 4-5 per cent CO2 and lowers oxygen, leaving about 1-2 per cent.
Sources
- Electronic Code of Federal Regulations, 21 CFR 866.2580, Gas-generating device (checked 2026-10-31): https://www.ecfr.gov/current/title-21/section-866.2580
- Saha S, et al. Indian Journal of Medical Research, 2016 (checked 2026-10-31): https://pmc.ncbi.nlm.nih.gov/articles/PMC5345310/
