WHAT’s UP WITH PEKING DUCK

It all started when I was researching pekin duck recipes. You see, pekin duck is a white-feathered breed of American mallard duck. Meaty and fast-growing, the pekin breed is perfect for a honey-roasted duck recipe I’m testing. The breed arrived in America in 1873 after a businessman successfully transported 9 prized ducks from Peking (a romanized name for Beijing, China). Years later, it’s a distinctly different from the breeds native to China.

Pekin duck is not Peking duck. At least not always. Peking duck, which also owes its name to a romanized name for Beijing, is a roast duck preparation that originated in Beijing. Known for its crispy, amber skin, a Peking duck’s skin is so brittle that it shatters like an eggshell. And yet the meat beneath the skin is tender, rich, and slightly sweet. It’s delicious.

Though Peking ducks were originally prepared with a black-feathered breed of duck from elsewhere in China, ironically, Peking duck is now usually prepared with American pekin duck. No wonder I was confused.

HOW PEKING DUCK IS PREPARED

Peking duck’s impossibly crispy skin is the result of a multi-day cooking process. It goes something like this:

1. The skin of the duck is sewed shut.

2. Air is pumped into the crevice between the duck’s skin and meat, allowing the skin to balloon and separate from the meat.

3. The duck is propped up, and boiling water is poured onto its skin until the skin tightens.

4. The duck is hung at room temperature overnight to dry out the skin.

5. The duck is — wait.

Ya, we’ve gotta stop. The duck is hung at room temperature overnight? You mean some uncooked poultry is kept in the temperature danger zone for like, an order of magnitude longer than it’s supposed to be there? And people eat this without getting sick?!

We’re going to have to get to the bottom of this. But first, the rest of the process:

5. The duck is glazed multiple times inside and out with a syrup made from soy sauce, five-spice powder, and other ingredients.

6. The duck is cooked in the oven until the skin turns its signature amber color.

Call me skeptical, but when I read the recipe, I straight up did not believe it. They sell Peking duck in multiple restaurants where I live, San Francisco. I’m certified to handle food in California, and I know it is simply not legal to serve meat that has been left uncooked at ambient temperature overnight. And for good reason! There’s just no way that the restaurants serving Peking duck in San Francisco are blatantly disregarding health code. Or so I thought.

Let’s talk FOOD Safety

To understand why this is so perplexing, let’s dive into the California Health and Safety Code. It’s pretty straightforward.

Time and temperature are two of the most important factors to control in the prevention of a food borne illness… Harmful microorganisms grow well in foods held between temperatures of 41 degrees Fahrenheit and 135 degrees Fahrenheit. This temperature range is also known as the Temperature Danger Zone (TDZ). The less time foods spend in the TDZ, the less time harmful microorganisms have to grow. Typically harmful microorganisms can grow to levels high enough to cause illness within four hours; therefore specific regulations in the California Retail Food Code related to the prevention of a food borne illness focus on reducing the amount of time foods remain in the TDZ.

Okay, so the danger zone is real — codified by law. The safety code doesn’t go into detail on the reasoning, so let’s go a little deeper. The USDA says:

Leaving food out too long at room temperature can cause bacteria (such as Staphylococcus aureus, Salmonella Enteritidis, Escherichia coli O157:H7, and Campylobacter) to grow to dangerous levels that can cause illness. Bacteria grow most rapidly in the range of temperatures between 40 °F and 140 °F, doubling in number in as little as 20 minutes.

Most sources suggest that food left in the danger zone for more than 2 hours (according to the USDA) or 4 hours (according to the CDE) should be discarded.

To be clear, these guidelines are meant to be foolproof 100% of the time, and there is certainly wiggle room at the edges of the temperature and time guidelines. Peking duck, however, is kept at room temperature for a whopping 12 hours — many times the amount of time recommended by the USDA! If scary bacteria like salmonella and E. coli indeed double every 20 minutes (I’m sure it’s actually more complex than that), then there is a billion times (2^[10*3]) more bacteria in a consumed Peking duck than in the food the USDA recommends you throw away.

But people aren’t dying. And restaurants are still serving (and are all allowed to serve) Peking duck. What gives?

THE PEKING DUCK Exemption

Thanks to an article in the San Gabriel Valley Tribune, I came to learn a bit about the history of serving Peking duck under the critical eye of health code. And to my surprise, the answer used to be this: Chinese restaurants would just pay the fine! They’d disregard the law and cook Peking duck the only way they knew how. Stubbornly, the restaurants considered the occasional health violation an unavoidable cost of doing business.

Over time, however, Peking duck’s reputation as a staple of Chinese culture and cuisine garnered more attention. In the early 80s, activists challenged the health code. One drove a Peking duck from San Francisco to UC Davis in Sacramento for laboratory testing. The lab tested, and they did not find unsafe levels of bacteria in the duck. The duck was safe.

In response, California took action in 1982. A new law was put into effect that provided a food temperature exemption for Chinese roast ducks and only Chinese roast ducks, granting them extra hours in the Danger Zone. The law states:

Raw duck that otherwise would be readily perishable shall be exempt from Section 113996 for a period not to exceed two hours, if the duck will subsequently be cooked at or above a temperature of 350°F for at least 60 minutes.

The code goes on to provide Chinese roast duck an exemption allowing cooked duck to hang at ambient temperatures, too. This law, in just a few sentences, is the Peking duck exemption, and it’s how many Chinese restaurants in San Francisco get by. Looks like there are similar exemptions in NYC, too.

THE SCIENCE

Now, the Peking duck exemption provides Peking ducks with more time in the danger zone, but not unlimited time. Observing from afar, I suspect that some Chinese restaurants are still skirting the law. But is it safe?

I found a food safety PhD, aptly called the Food Safety Guru, to get to the bottom of this. According to Dr. Nummer, the science shows that Peking duck is actually pretty safe. From the Guru:

A HACCP and microbial model risk analysis was performed on the Peking duck culinary process for foodservice. The largest concern for the process is a prolonged ambient temperature drying process. The traditional process uses salt, sugar, and acid as growth inhibitors to minimize the potential for pathogen outgrowth during the extended ambient drying process. Modelling of both S. aureus and C. perfringens demonstrated that in a worst case scenario (pH 7 Aw 0.98) no growth of either S. aureus and C. perfringens occurred in 8.5 hours at 25°C/77°F. Under these same conditions it took more than 14 hours to reach 104 cfu/g. No growth of either S. aureus and C. perfringens occurred in 14 hours at 25°C/77°F when the pH and Aw were factored in of this food product.

Translation? The peculiar method of cooking Peking duck is surprisingly effective at preventing bacteria growth, because both the marinade and the drying process increase the acidity and decrease the water activity of the dish. I wrote more about how acidity and water activity can prevent bacteria growth here.

I’ve also found comparable studies on similarly crispy-skinned Chinese roast pork that conclude that, between the low water activity, the marinade’s antimicrobial characteristics, and the final cook with very high temperatures, the food is surprisingly protected from excessive bacteria growth.

So the science is on our side — Peking duck is safe. And I’m thankful that California food code has taken such science into account when allowing deviations from best practice. You can count me in for the next round.