PURPOSE: To provide an efficient treatment by finding a point of regeneration of filtration medium by backwash, by observing an increase in pressure drop by simultaneously passing a part of a contaminated fluid at a higher speed and a small scale when passing the contaminated fluid through the filtration medium.

CONSTITUTION: A filtration system is provided for manufacturers mass producing beer and wine by batch method. A contaminated fluid is passed through a filtration system comprising a first filtration medium having a predetermined surface area. Next, a part of the contaminated fluid is passed through a monitoring system comprising a second filtration medium having a predetermined surface area though a smaller surface area than the surface area of the first filtration medium at a rate per unit of area greater than a rate of the first filtration system. By observing an increase in pressure drop of the quantity of the fluid passing through the second filtration medium per unit of surface area, the passage of the contaminated fluid through the first system is terminated before the quantity of the fluid passing through the first filtration medium exceeds the second quantity of the fluid and the increased pressure drop is caused.