According to Blue Bell Creameries supplier Aspen Hills Inc., the cookie dough ingredient it provided the ice cream company was free from listeria when it was tested prior to delivery.

Blue Bell recently initiated a voluntary recall of two of its ice cream products, citing possible listeria contamination in the cookie dough it uses. Blame for the contamination then should fall on Aspen Hills, being the source of the ingredient, but the supplier said the cookie dough sent to Blue Bell tested negative for the bacteria before leaving its facilities.

"We are always trying to look for ways to be better, and food safety is one of those areas," said Jon Austin, Aspen Hills spokesperson.

Blue Bell was the only recipient of the cookie dough ingredient produced by Aspen Hills. According to the supplier, it has never recalled any of its products for whatever reason.

So, who's really to blame?

It won't be clear until further tests have been carried out, but Craig Hedberg, an environmental health sciences professor from the University of Minnesota, said that listeria persists in food products for an extended time period. Given the bacteria's nature then, it's actually possible for both Blue Bell and Aspen Hills to be telling the truth.

If so, the likely scenario was that, at the beginning, the cookie dough ingredient had listeria levels so low that the check Aspen Hills carried out was not able to identify the bacteria's presence. However, because Blue Bell sat on the ingredient for two months, it's possible that Listeria monocytogenes was given time to proliferate, raising the bacteria's level to the point that it was detected by test-and-hold procedures followed by the ice cream company.

After it's listeria recall in 2015, Blue Bell signed an agreement with health officials from the three states where it has production plants. Part of the agreement was that inspections will be routinely carried out. Comparing information from Alabama, Texas and Oklahoma, however, revealed that inspections in Alabama, where the recalled products were made, are fewer than what health officials in Texas and Oklahoma had conducted.

Where tests in Oklahoma were scheduled monthly, Alabama's was done quarterly. Texas, on the other hand, saw 22 equipment tests since Blue Bell resumed operations in November.

Having another recall within a two-year period is not good for Blue Bell but the ice cream company is not alone in facing the challenges of food contamination. Recently, Kellogg's also voluntarily recalled its Eggo Nutri-Grain Whole Wheat Waffles over listeria concerns.

Products affected by Blue Bell's most recent recall are its Chocolate Chip Cookie Dough and Cookie Two Step ice creams.