I need to monitor the microbe contamination in wort using agar plates. currently, im using membrane filtration method. for this, i need to filter 100 ml wort sample through 0.45 micron filter paper and transfer it on mygp+cu agar media to detect wild yeast. then, incubate it in 25 degree celcius for 48-72 hours. but, the sample get stuck after filtering about 30 ml. it is still the same even though i let the wort sample to get settle before the filtration. my questions are

1. can i use 30 ml wort sample for this method?

2. should i shake the wort sample before filtration or let the sample to get settle?

3. what is the tolerance/standard level of cfu/ml if i use 30 ml of wort sample?

please provide reference. Thanks.