Sampling Low-Density Populations

In cases where microorganisms are either absent or present at very low levels ( 5 CFU/L), such as bottling line or prebottling samples, the ques- 

As seen, the difference between stability and potential refermentation is less than 1 colony/plate and, in this example, most likely would not be recovered. This situation is obviously well below the comfort zone of most people. Using the same tolerance levels as above, compare the results using 750 mL of sample  

Although the theoretical ability to detect contamination has improved, the reader will recall that results are still well below minimal CFU/plate requirements of 30. (See Sec. C.2) What is the minimum volume of wine needed to detect 10 viable cells per liter Using the above relationship and some mathematical manipulation, it can be calculated that a minimum of 3000 mL (3 L) would need to be filtered to develop 30 colonies/plate. For this reason, bottling lines often utilize in-line samplers that continuously sample the wine. These are equipped with a membrane filter that can easily be disassembled and a new one replaced at regular intervals. 

Autoclaved filter housing, vacuum flask, and tubing Prepackaged sterile Petri plates and 47-mm presterilized membrane filters (0.45 Xm—see Supplemental Note 1) 

Agar plates or media-impregnated pads (see Supplemental Note 2 and Appendix A) 

---