Hey guys, my story with Coliform count on Green Tea ice cream has a continuation and surprising finale. For years, we've been having this discrepancy between our Coliform testing results and the accredited lab ones - though, we used the same testing methods (Petrifilm). Our testing always showed clean while lab's showed count (though - never E. Coli). We've wracked our brain figuring out why that was happening - and finally, when the company owner had a discussion with the lab personnel, including lab head and techs, it appeared that lab techs didn't do their job right! They counted gas bubbles as Coliform colonies - but those bubbles were just the air bubbles (due to the nature of ice cream having incorporated air). The company owner showed them a testing guidance clearly describing what should be considered Coliform colonies, and what - not. I'm just outlining a situation for whomever were under similar circumstances.
Hi Olena,
I'm guessing the dispute involved use of VRB medium.
If so, this also has another potential error (depending on the product type), non-specificity for Coliforms giving high, sometimes very high, counts. Have had several "ding-dongs" with customers over this.
At low levels, MPN is IMO without competition (was developed for such situations). Unfortunately many Labs are unwilling to pay/wait > 1 day.