Between initial tests and larger scale up you may want to conduct intermediate scale recombinant protein production using baculovirus vectors. If you are working with several constructs then this can begin to get expensive of cell culture vessels such as the ubiquitous 125ml conical flasks, in which you can amplify 25-30mls of virus-infected cells. Space on shakers can also be at a premium in some labs.
To address both the cost and space issues we have recently been testing the use of 25ml mini bioreactors for intermediate scale recombinant protein production. These are simply 50ml volume disposable centrifuge tubes with a screw cap. You can buy them with a ventilated lid, although we have found that unventilated ones work just as well if you leave the lids loose but stop them falling off with a piece of tape.
These 50ml tubes can propagate up to 25ml virus-infected insect cell cultures rotating at 250 rpm. This high speed enables sufficient aeration to keep the virus replication process optimal. It may seem that the surface area/volume ratio is unfavourable for gas exchange but it seems to work.
Another advantage of carrying out intermediate scale recombinant protein production in these tubes is that you can harvest the cells using the same vessels. There is no need to transfer them to new tubes prior to sedimentation of the cells. This helps to streamline the process.