Preparing a benchtop fermenter for autoclaving is a critical step for achieving reliable, contamination‑free fermentations. The process can seem daunting, but by breaking it down into clear stages you can move smoothly from cleaning and assembly through to sterilisation, calibration and inoculation. This guide walks through the essentials for preparing a 2L Solaris Jupiter autoclavable fermenter.

Pre‑Autoclave Preparation

The first step is to thoroughly clean and inspect every component of the fermenter. Wash the vessel, headplate, impellers, baffles, O‑rings and fittings with laboratory detergent, then rinse them with distilled water to remove any residue. Look carefully for cracks or signs of wear, paying particular attention to O‑rings, which should be replaced if damaged. A very light application of silicone grease to seals is sometimes recommended, but take care not to over‑apply. Once all parts are ready, reassemble the vessel according to the user manual: install impellers at the correct height, refit baffles and other accessories, and seat the headplate evenly. Tighten the clamps firmly by hand so that the O‑ring compresses to form a proper seal. Every port should either hold the correct component or be closed with a sterile plug.

Adding Medium and Antifoam

Before sterilisation, the culture medium should be added directly to the vessel. Fill to around 25-75% of the working volume, leaving headspace needed for aeration and prevent spill‑over during boiling. It is sensible to add an extra 5–10% water to offset evaporation during the autoclave cycle. If foaming is expected, mix in a small amount of an autoclavable antifoam, typically 0.005–0.01%. This distributes evenly through the medium and helps avoid excessive froth later. At this stage, check again that valves and septa are firmly in place, and cover exposed fittings with foil.

Installing Probes

Sensors such as pH and dissolved oxygen (DO) can be installed before sterilisation, covering the connector ends with foil. pH electrodes should be calibrated in buffer solutions before fitting, then rinsed and inserted with care. Optional sensors such as foam or level probes can also be positioned now. Temperature probes are inserted into their thermowell post autoclave since they do not have direct contact with the culture.

Gas and Liquid Connections

To ensure sterility while allowing proper gas exchange, both inlet and exhaust lines must be fitted with 0.2 μm filters. The sparger line should be clamped closed for autoclaving, while the exhaust filter must remain open to allow pressure to vent safely; both filters should be covered with foil. Additional lines for feeds, acid, or base should be connected to bottles equipped with vent filters. Heat‑stable solutions can be autoclaved directly; for sensitive feeds, autoclave water instead and replace with sterile solution afterwards under aseptic conditions.

Autoclaving

The fully assembled vessel is now ready for sterilisation. Place it upright in the autoclave, ideally in a tray that can contain any spills, and include any connected reagent bottles. Run a liquid cycle at 121 °C for 20–30 minutes with slow exhaust. This gradual cooling prevents boil‑over and protects both the medium and the vessel. The exhaust filter must remain open throughout the cycle to allow pressure equalisation. Once the autoclave finishes, let the vessel cool naturally before handling.

For guidance on the next steps, refer to the ‘How to set up a Jupiter’ tutorial video at the end of this guide.

Post‑Autoclave Setup

When the fermenter has cooled, move it to a clean area and reconnect it to its control system. Attach the motor drive, connect sensor cables, and link up the aeration supply. If bottles were autoclaved with water, replace the contents with sterile acid, base or feed solutions under aseptic conditions. Begin temperature control to bring the vessel to the correct setpoint, and then check calibrations: confirm that the pH reading is accurate at temperature, calibrate the DO probe at 100% air saturation (and 0% if needed), and ensure that the foam probe is functional.

Ready to Inoculate

At this stage the fermenter is sterile, calibrated and equilibrated. Inoculation can be carried out aseptically using a septum or sampling port. Once the culture has been introduced, resume aeration and stirring: a fall in dissolved oxygen levels is usually the first sign of microbial activity. From here, the fermentation can progress in batch mode before feeds are introduced as part of your chosen fed‑batch strategy.