Determining the total weight of a culture is a tedious and time-consuming method that is not used routinely. It can be invaluable, however, for measuring the growth of filamentous organisms. These do not readily break up into individual cells, which are necessary for a valid plate count. To measure the wet weight, cells growing in liquid culture are centrifuged down and the liquid removed. The weight of the resulting packed cell mass is proportional to the number of cells in the culture. The dry weight of the cell mass can be determined by drying the centrifuged cells at approximately 100°C for 8 to 12 hours before weighing them. About 70% of the weight of a cell is water.
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