If the Cult of Diet Coke were an actual cult, I would be its Squeaky Fromme (totally devoted, weirdly hot). Some of my earliest foodie memories are of pairing Diet Coke with Oreos at vacation bible school, but I didn’t realize the no-cal beverage and I were so close in age. The silver can turned 4o this week, which seems both too old and too young at the same time. (Coincidentally, that is exactly what I imagine turning 4o feels like.)
On an alignment chart, Diet Coke is a chaotic neutral. Its tart, bubbly, bracing nature pairs with the sweet and the savory—even Thanksgiving dinner—and avid Diet Coke enjoyers have been know to enjoy her at breakfast, lunch, and dinner.
I really don’t know any casual Diet Coke drinkers, now that I’m thinking about it. Every single one of us has a sick little Diet Coke ranking system, which we love to share with anyone who asks (or doesn’t ask). Opinions on cans versus bottle tend to vary from drinker to drinker, but virtually every Diet Coke-head agrees that a McDonald’s fountain Diet Coke is the apex of diet soda enjoyment. (The other thing we agree on? Diet Pepsi is never “OK.”)
There are three factors that make McDonald’s Diet Coke so perfect: Consistent syrup-to-water ratios, temperature control, and that beautiful straw. And though you may never have your own personal Diet Coke fountain, you can use the McDonald’s principles to create your best Diet Coke drinking experience at home.
It starts with the syrup
The differences between McDonald’s Diet Coke and other Diet Coke starts with how the syrup is transported to the restaurant. According to the New York Times, most syrup is transported in plastic bags, while McDonald’s has theirs delivered in stainless steel tanks, which keeps it fresher, longer.
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Then there is the matter of consistency and chilling (and chilling consistently). If you’ve ever encountered a fountain soda made with “off” syrup-to-water ratios, you know it can be an unpleasant experience, especially if that soda is Diet Coke (aspartame is a fickle beast). McDonald’s prevents such a disaster by following an exact ratio and keeping everything super cold. From their website:
We ensure our Coke products are fresh and always tasting the way they should by following the guidelines set by Coca-Cola, using a ratio of syrup that allows ice to melt, and pre chilling the Coca-Cola syrup and water before they enter our soda fountain!
Why does temperature matter?
Warm Diet Coke is disgusting. It feels flat on the tongue, and has a unique flavor best described as “blood and metal.” According to the New York Post, McDonald’s “soda water is constantly recirculated through this tubing system so that it can remain between 33-38 degrees (just above freezing) at all times.”
Keeping the beverage cold not only helps it read as more refreshing on the palate, it keeps it fizzier. Cold liquids hold onto gases better than warm liquids—i.e., gas is more soluble in a cold liquid, but according to Sciencing.com, changes in temperature and pressure can also affect pH and, as a result, flavor:
The taste of carbonated drinks depends on the temperature at which they’re stored. This can be explained by the fact that temperature has to be lowered to stabilize the content of carbon dioxide. The resulting conditions will lower the pH to between 3.2 and 3.7, giving the drink a sour taste that describes typical soda flavor. This is the reason why carbonated beverages should be consumed when cold.
This lack of sourness in warm Diet Coke is what makes it taste unbalanced and metallic, which is why McDonald’s takes temperature so seriously.
A straw can only do so much
The McDonald’s straw is a perfect straw. It’s wider than most, which allows for more bracing bubbles per sip, but even the best straw can only do so much when confronted with a warm or flat beverage. To test the power of the straw, I went and picked up a large fountain Diet Coke from McDonald’s along with a 1-liter bottle from my local Plaid Pantry convenience store.
I tasted the Diet Coke five different ways: From the McDonald’s cup, through the McDonald’s straw; directly from the 1-liter bottle, without a straw; from the 1-liter bottle, through a McDonald’s straw; and poured into a glass with ice, both with and without the straw.
The McDonald’s fountain Diet Coke was the best, but drinking through the McDonald’s straw from the 1-liter bottle was a very close second, and only because it was slightly warmer, and thus not as bracing.
The Diet Coke I poured into a glass was terrible, almost completely flat tasting—especially when sipped after and compared to the McDonald’s soda—but that makes sense. Opening a bottle (or can) of soda releases pressure and carbonation, but pouring it into a glass with ice introduces nucleation sites, which encourage fizzing, releasing carbonation from the liquid into the air. This is why soda foams so aggressively when you pour it, and why I never ask for a glass with my can of Diet Coke. Even the best, widest straw can’t fix a nearly flat soda—it doesn’t matter how many bubbles it can fit if there are no bubbles to deliver.
What is to be done?
It’s not possible to replicate the McDonald’s Diet Coke delivery system at home, but there are things we can learn from the fast food giant’s methods.
Keep your Diet Coke as cold as possible (without freezing), by storing it in the coldest part of your fridge, or popping it in an ice bath (like you would champagne) before serving. You should also avoid transferring the soda from its original container to a glass, which is why it’s a good idea to avoid larger bottles (like 1- and 2-liters) and cans (such as the tallboys) altogether. Not only do those often necessitate pouring into a secondary container, they lose carbonation every time you open them.
Lifehacker’s senior health editor, Beth Skwarecki, (a fellow Diet Coke head) likes “the 500-milliliter bottles specifically,” so that she “can keep the cap on and keep the fizz in.” And I tend to opt for the standard can, because the aluminum chills with the beverage, and I drink them fast enough so they stay fizzy until the last drop.
When choosing a fountain beverage, know that not all machines mix and dispense the soda in a standardized way, so find a good one and be loyal to it. in the words of Lifehacker’s senior tech editor, Jake Peterson, “A good fountain Diet Coke is my go-to, but I’m always wary, because bad fountain soda is baaaaad.”
And of course, it never hurts to grab an extra straw from the drive-through. It won’t save a flat cup of soda, but it will let more carbonation hit your tongue per sip (if there is any carbonation to be had), improving your Diet Coke drinking experience, whether you’re sipping from can, plastic 20-ounce, or fancy glass bottle.