If you're a fan of burgers – and let's face it, a lot of us are – we have good news and bad news. The good news is that a recent molecular analysis of more than 250 samples of burger products in the US has found that the vast majority of patties are pretty much what they say they are in terms of ingredients and nutritional analysis, and don't contain any unsavoury surprises.

The bad news? Well, it seems an unsettling 14 percent of the burgers analysed were flagged for one issue or another, with products sampled demonstrating problems with either contaminants, hygienic issues, or ingredients inconsistencies.

The analysis was run by Clear Labs (formerly Clear Foods), a US-based genomics testing lab that analyses food on behalf of consumers and the food industry. The same group ran a DNA analysis of hot dogs last year, which also turned up a few nasty surprises.

This time around, Clear Labs tested 258 samples of ground meat, frozen patties, veggie burgers, and fast food sourced from 79 brands and 22 retailers across California – although many of the products are available elsewhere in the US too.

One of the most prevalent issues the team found was substitution, where unlisted ingredients were contained in the foods tested. Almost 7 percent of burgers sampled contained ingredients they weren't supposed to, including unlisted beef, chicken, turkey, pork, rye, and sunchoke (aka Jerusalem artichoke) – including two cases of meat in vegetarian products.

As the report points out, substituted ingredients can be a problem for people with allergies, and also for those avoiding certain foods for cultural reasons.

Vegetarian burgers in particular didn't fare well in the test, with 15.7 percent of the vegetarian products missing ingredients from those listed on their labels. Of these, the worst offender was a 'black bean vegetarian burger' that didn't actually contain any black beans!

"While this may not have been an intentional omission," the report reads, "it uncovers a surprising and potentially serious problem with quality control in the manufacturing of vegetarian burger products."

Perhaps even more disturbing than dodgy ingredient labels are hygienic issues, which cropped up in 1.6 percent of the samples. The researchers note that human DNA was detected in one frozen vegetarian burger, and rat DNA was found in three products. While the report makes clear that these low levels of foreign DNA are unlikely to be harmful to health, it's a salient reminder that food-handling protocols will inevitably have an impact on a very small percentage of the things we eat.

Likely more harmful would be pathogenic contaminants, which the researchers found in 4.3 percent of burgers analysed, including DNA of Yersinia pseudotuberculosis in four samples, which can cause tuberculosis-like symptoms. Other pathogens detected in patties included Yersinia enterocolitica, Aeromonas hydrophila, Clostridium perfringens, Klebsiella pneumoniae, and Escherichia coli.

According to the scientists, the biggest issue across the board – although not necessarily the most serious in terms of health – was nutritional variation, with 46 percent of samples containing more calories than listed on the labelling, and 49 percent containing more carbohydrates.

While the report makes scary reading at times, analyses like these aren't intended to gross everybody out about the foods we eat. The researchers are reporting their findings to keep consumers and the food industry itself informed on what's actually contained in these foods, so safety, quality, and consistency can all be improved.

"As it turns out, the most consistent area for improvement is consistency itself," the authors write. "While several subsets of the industry have championed food safety, others such as vegetarian products have fallen behind. Similarly, end-product consistency continues to disparage public perception of the burger industry."

Ultimately, if you're not happy taking your chances with the issues outlined in the report, it might be an idea to just make your patties at home – which is probably better for you anyway.