Laboratory culture Erlenmeyer flasks: how can oxygenation and growth under agitation be promoted?

Essential on any orbital shaker, shaking flasks deliver homogeneous mixing and efficient aeration of media. From screening through to scale-up, they stabilise oxygen supply to the medium, reduce gradients and make your growth or reaction kinetics more reproducible. Reusable glass or sterile plastic, baffled or plain, vented caps or filter closures: every detail affects oxygen transfer, shear stress and microbiological cleanliness. Choosing the right flask safeguards your yields… and your timelines.

What are the different types of shake flasks, and how do you choose?

Two broad families define usage: ?1 L flasks for screening and optimisation, and >1 L flasks for concentrated pre-cultures and scale-up. On top of that come the geometry (classic Erlenmeyer, wide-base Fernbach), the presence of baffles (higher OTR) and the material. Borosilicate glass is autoclavable, durable and chemically inert. Sterile PETG or polycarbonate (PC) options, with 0.2 µm filters, reduce cleaning and contamination risk.

The choice depends on shear sensitivity (CHO/HEK cells favour unbaffled flasks), the required aeration level, the orbit and speed of your shaker (e.g., 19–50 mm, 120–250 rpm), the fixing system (clamps, peg platforms, adhesive mats) and sterilisation constraints. Also consider the working volume (20–30% of nominal volume), chemical compatibility and the environmental footprint: reusable glass vs single-use.

For guidance, see the comparative table below:

Type	Use	Benefits
? 1 L	Screening, media optimisation, small batches	Easy handling, high sample density, fast mixing dynamics
> 1 L	Pre-cultures, scale-up, pilot lots	High oxygen transfer (Fernbach), large working volume, smoother bioreactor transfer
Baffled vs smooth	Yeasts/bacteria vs sensitive cells	Baffled = increased oxygenation; Smooth = lower shear and less foaming

On closures, vented caps and filter caps maintain gas exchange while protecting against contamination. Foam/silicone stoppers remain relevant with glass. Finally, check compatibility with your platform (clamp footprints) and the environment (CO? incubation, temperature, prolonged shaking).

In which application areas are shake flasks used?

• Life sciences/bioproduction: microbial and mammalian cultures (E. coli, CHO, HEK), protein expression, enzyme production, inoculum preparation for bioreactors.
• Pharmaceutical: strain screening, media optimisation, solubility and stability studies, preformulation.
• Agri-food: yeasts and fermentations, starter cultures, flavour/enzyme optimisation tests.
• Environment: biodegradation assays, enriched cultures, consortium monitoring.
• Chemistry/cosmetics: liquid–liquid extractions, dispersion of actives, deagglomeration, API solubilisation.
• Education/analytical R&D: sample preparation, homogenisation prior to analysis.

Their key benefit: tight control of oxygenation and shear, close to bioreactor conditions—ideal for DoE, standardisation and inter-laboratory reproducibility.

Available types of shaking flasks

Frequently asked questions about shake flasks

What is the difference between a flask with baffles and a plain one?
Baffles increase oxygen transfer and mixing, useful for yeast/bacteria. Plain (unbaffled) walls limit shear and foam, better for sensitive cells.

What filling volume is recommended?
Aim for 20–30% of the nominal volume. Adjust for orbit (19–50 mm), speed (rpm) and how sensitive the culture is to foam/shear.

PETG or polycarbonate: autoclavable?
PETG is generally not autoclavable. PC and borosilicate glass are. Sterile plastic flasks are often gamma-sterilised.

Which caps are best for aeration?
Use caps with 0.2 µm filters: they allow gas exchange while protecting against contamination.

How to secure high-speed shaking?
Choose compatible clamps, balance the loads, centre the flasks and respect the orbit/rpm limits specified for your shaker.

Are flasks >1 L suitable for CHO cells?
Yes, unbaffled, moderate speed and a vented cap. Monitor foam and shear; Fernbach flasks are preferred for gentler aeration.

Reusable glass or single-use: what to choose?
Glass = durability and chemical inertness; single-use = speed and controlled risk. The choice depends on your workflows, validations and ESG objectives.