Why McDonald's Big Mac Sauce Tastes Like Tomato Sauce

Burger fans recognise the power of the special sauce, whipping up their own custom batches to recreate the savoury, delectable bite they know and love from their favourite burger chains. Usually, those sloppy creations mirror thousand island dressing: tomato sauce and mayonnaise, tomato sauce, relish and mayonnaise, tomato sauce, relish, mustard and mayonnaise, et cetera. Except here's the thing: there's no tomato sauce in the most common burger au jus, the McDonald's Big Mac Sauce.

Image: Ryan F. Mandelbaum

McDonald's in the US released ten thousand numbered bottles of its Big Mac Special Sauce as part of a promotion. I was able to acquire a bottle after begging McDonald's PR department in an email. Once it arrived, I immediately looked at the ingredients. Having always assumed Big Mac Sauce is just pumped-up thousand island dressing, I was baffled to learn there wasn't a tomato to be seen on the entire ingredient list.

Oil, vinegar and egg yolks, the core ingredients for mayonnaise, take up positions one, three and four. Relish and its components occupy the two slot. I'm not really worried about the preservatives or thickeners, like potassium sorbate, sodium benzoate, alginate or xanthan gum. So, where on Earth does the savoury tomato-like flavour come from? I asked an expert.

"So you're telling me this tastes like tomato sauce?" asked Devin G Peterson, director of the Flavour Research and Education Center at The Ohio State University, when I showed him the ingredients. I explained, no, I just always assumed it was Thousand Island dressing, which happens to have tomato in it. But then he found something.

"This makes sense," he said. He explained that the hydrolysed proteins on the ingredient list are similar to proteins that have already been digested by your body, which I took to mean proteins broken down into amino acids. Monosodium glutamate -- not on the ingredient list -- also consists of amino acids, namely, glutamic acid with sodium molecules attached.

"Tomatoes have a high amount of MSG", Peterson said, explaining that our tongues perceive MSG as umami, the savoury flavour that accompanies mushrooms and Parmesan cheese. "I think the hydrolysed proteins give you umami... I'm going to suggest it's the hydrolysed proteins that gives it the tomato taste."

I googled around and confirmed that Serious Eat's J. Kenji López-Alt came across this same chemical property while trying to recreate his own burger sauce. To give your own little kitchen experiment that umami flavour, he suggests using a yeast extract like Vegemite.

It's unlikely you'll get your own bottle of Big Mac Sauce, but if all you want is the flavour, it's just mayonnaise, relish, some spices (garlic powder and onion powder, though mustard will do) ... and Vegemite.

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