Orbit and speed on an orbital shaker: how to keep bacterial growth consistent

Orbital shaker speed drives oxygen transfer

Orbital shaker speed directly affects aeration in bacterial cultures. Oxygen has limited solubility in liquids. Therefore, shaking is essential to supply dissolved oxygen. Agitation pushes liquid up the flask walls. This increases the air-liquid surface area. Consequently, oxygen transfer into the medium improves. Temperature control remains important for stable growth. For suitable systems, see Shaking and Mixing.

Orbital shaker speed and orbit scale OTR linearly

Orbit diameter has a linear relationship with Oxygen Transfer Rate, or OTR. If orbit diameter doubles, OTR doubles as well. Moreover, OTR has a roughly 1:1 relationship with agitation speed. In one example, 150 RPM reached a maximum OTR of 11. At 300 RPM, the maximum OTR was 20. This used a 250 mL flask with 26 mL volume and a 2 inch orbit. However, increasing speed too much can create shear and damage cells. For selection guidance, visit Shakers and mixers for laboratories.

Working volume and flask choice shape reproducibility

Flask size and working volume strongly influence aeration performance. Therefore, recommended culture volume is about 10–25% of flask volume. For a 2 liter flask, 200–500 mL is recommended. A smaller volume maximizes the air-exposed surface area. Baffles are not recommended because they increase splashing. Consequently, foam can overflow or increase contamination risk. Document these choices in SOPs to reduce variability.

Orbit conversion formula for switching between shakers

When moving to a different shaker, you want similar liquid movement. Therefore, the goal is matching force and acceleration across platforms. Mass stays constant with the same flask and volume. Acceleration depends on speed and the orbit radius. The application note provides a conversion formula using d1, d2, r1, and r2. In one example, 1 inch at 300 RPM moved to 0.75 inch orbit. The prediction was 346 RPM, while 350 RPM worked empirically. Another example moved from 18 mm at 230 RPM to 25 mm orbit. The prediction was 196 RPM, while 200 RPM performed best. Finally, support consistent performance with service and maintenance and preventive maintenance.