Hardware investment for process control represents an important part of the global cost of a small-scale project and low cost solutions do not respond as well as robust systems. Combining the low cost of the on-off actuators with the robustness of classical controllers could produce good results in variable control. Three strategies were used in order to obtain temperature control in fermentation runs of Bacillus thuringiensis. The first was control on-off, which is the simplest method to achieve variable control by using on-off valves. The second is a modified on-off with waiting time, which allows the system a pause before sensing the variable value; therefore, the size of the variable overlaps are reduced. Finally, a combination of on-off valves with a. temporized virtual-PID controller (PIDt) was developed and implemented, and accurate control of temperature during the fermentation process was obtained. This last variable control strategy uses an algorithm which may be easily implemented by a non-specialized computer programmer. An additional advantage of the results obtained include an 82% reduction in the cost of valves by the use of non-conventional techniques and programming tools.