I have seen many record state a burger can be served a little pink. Even 'medium'. I understand what this means.
My question is about food safety: Is this also safe if the patty was a mix of beef and pork?
I can use common sense and predict if there was only 1% pork, then it is probably safe, but assuming the meat comes from a supermarket and is a 50:50 mix, is it recommended to cook this well done?
In most developed countries trichinosis is extreme rare, this is due to changes in the way pigs are raised. In the US there were only 16 cases reported between 2011-2015, for example, and in Europe the rates are similar. This means that you could serve pork completely raw with extremely low risk from a trichinosis point of view.
In a 50/50 beef-pork burger you have an equal amount of risk from the beef as the pork due to e coli bacteria, the meat really doesn't matter. Safety guidelines are to cook ground meats of any kind to 70°C/160°F, which is well done. As to whether you follow that guideline is up to you, millions or people have their burgers pink in the middle and it's rare anyone gets sick so the risk is small, but it's still there. Whether you take that chance is personal choice.
Sure you can! I think you're conflating two aspects of cooking meat here:
Doneness: whether your meat turns out rare or well-done depends on the maximum temperature the meat is cooked at.
Food safety: this is a function of both cooking time and temperature.
To combine the two, you can have a food safe burger cooked rare if it's cooked at a low enough temperature for the meat to stay rare and at a high enough temperature (for enough time) to kill most bacteria.
GdD is right that a burger through at 70°C/160°F is food safe. Most of the bacteria will die within seconds at that temperature. Using the sous-vide technique, however, it's quite easy to get a food-safe medium doneness by cooking the burger at a lower temperature (say 57°C/135°F) for a little over an hour (see the time temperature chart for pasteurization on Serious Eats, for example).
Pasteurization times at lower temperatures might be inconvenient, but even then you can kill many bacteria in a few hours and still have a rare burger.
By rapidly cooling the burger after the sous vide step and reheating it in the pan (on the grill / under the broiler) you can have your desired doneness and a nice maillard reaction on the outside with minimal risk. In that example the cooling step ensure that you don't overcook the inside of the burger when you give the outside a good sear.
I wouldn't say it's a 'daft question'. Some markets do sell pre-mixed ground pork-and-beef mixtures intended primarily for meatballs or meatloaf, so it's reasonable to wonder if that mix can be used for burgers, too, but there are too many variables not accounted for.
The problem is that we have no way of knowing what standards the hypothetical market in the question meets. Is it located in a country where trichinosis is all but extinct, like the US or Germany, or a country where pigs are still raised in pits of mud and feces? Do the market's butchers practice safe meat-handling?
In the best of all worlds, you could eat both pork and beef completely raw and be perfectly safe. In our world, pigs raised in filth may well have parasites including trichinosis. Cattle do not normally harbor anything harmful to humans, though there was the "mad cow" outbreak a couple of decades ago, but people can be disgusting in their lack of hygiene, so there is still risk.
Then there are the definitions. What is 'medium'? The worst trichinosis infection will be neutralized once the meat reaches 155F, but that is essentially medium-well and the USDA, which only cares about safety and not edibility, recommends 160F for GROUND beef, pork, veal, and lamb. They recommend 165F for ground chicken/turkey.
It's worth noting that even the USDA no longer recommends cooking solid cuts of pork till it's petrified. While they don't give a recommendation for Rare, they do specify a temperature of 145F for Medium-Rare Pork (or beef, lamb, veal, etc.). Ground meat is always more risky than solid cuts, but that's a different question.
But, then you say "a Burger can be served a little pink. Even 'medium'. I understand what this means." I don't think you do. Medium is a little pink. Medium-Rare is pink-to-red, but warm in the center. Rare is red and cool in the center. They are ALL SAFE if prepared correctly.
The mania for warning people away from 'under-cooked' burgers is due to our lawsuit-crazed culture, not food safety. The safety risk is due to people not washing their hands properly and not keeping their cook stations clean, not due to inherent risks from the meat. Cooking burgers till they become hockey pucks does render them harmless, and employers know that they suck at enforcing safe practices in their kitchens, so they shift the risk/blame to the customers.
If you trim and grind your own meat at home, and practice safe standards, you're perfectly safe in cooking your pork-and-beef burger Medium-Rare, which is how all burgers are at their best. But I wouldn't recommend it with the store-bought mix. Save that for your meatballs.
