This is were you can find frequently asked questions about shakingtechnology. You can receive special information about different shaken bioreactors under the respective entry. If you cannot find a solution for your problem, please contact our "Dr. Shaker"-team of experts.

Though seldom noted in the literature the shaking diameter exerts a major influence on the cultivation. Usually raising the shaking diameter increases the oxygen transfer rate. You can find more data in the publication of Maier and Buechs:
Characterisation of the gas-liquid mass transfer in shaking bioreactors
Maier U, Buechs J.
Biochem Eng J. (2001);Vol. 7, No. 2, pp 99-106

Tinfoil keeps the cotton plug dry in the autoclave. It should be removed prior to a cultivation to avoid impeding the gas exchange through the plug.

E. coli is a very respiratory active microorganism so the filling volume should not exceed 5 - 10 % of the total flask volume (i. e. 10 to maximum 25 mL in a 250 mL flask). Recommended culture conditions for the aerobic cultivation of E. coli in a 250 mL wide neck flask with cotton plug are as follows:
10 mL filling volume
300 rpm shaking speed
50 mm shaking diameter

Sampling reduces the filling volume. The oxygen transfer rate in the corresponding flask is therefore enhanced. Hence, culture conditions of sampled and unsampled flasks are comparable only to a limited extent. It is best to schedule an appropriate number of flasks so that one entire flask can be harvested for sampling.

The following publication describes a measurement method for determining the oxygen transfer rate in shaking flasks:
Online respiration activity measurement (OTR, CTR, RQ) in shake flasks
T. Anderlei; W. Zang; M. Papaspyrou; J. Buechs;
Biochem Eng J. (2004); Vol. 17, No. 3, pp 187-194
Experimentally you can make up several shake flasks with different filling volumes in parallel. If you get different results, then oxygen transfer could be the cause.

The neck geometry of the flask plays a bigger role in cultivations than the plug. Generally wide necks are beneficial for gas exchange. Under normal conditions the mass transfer resistance of sterile closures is far smaller than the resistance of the gas-liquid interface. A new method to determine the mass transfer resistance of different sterile closures by measuring the water evaporation rate was published in:
Mass transfer resistance of sterile plugs in shaking bioreactors
Mrotzek C, Anderlei T, Henzler H, Buechs J
Biochem Eng J. (2001);Vol. 7, No. 2, pp 107-112

The mechanical stress is higher in larger flasks at similar shaking frequency, because the liquid has to cover a longer distance in the same time with an elevated velocity.

Disposable shake flasks cultivated in a moisturized and carbon dioxide enriched atmosphere are frequently used for animal cell cultures.