Why You Can't Use Basic Food Dye To Make Colorful Ice Cubes - Tasting Table

"A Redditer suggests that the culprit may be propylene glycol, a food-safe anti-freeze, stabilizer, and emulsifier which is often found in food coloring. Propylene glycol can prevent food coloring from freezing, or increase the time it takes to do so. In addition to the coloring potentially failing to freeze, water never freezes uniformly. Instead, the edges, bottom, and top of an ice cube freeze before the middle."

"Food coloring isn't the only way to make colored ice cubes. Other options include fruit-infused water, herbal teas you can make at home, or even using edible flowers to give your water vibrant, natural colors. There are hundreds of options for making fun, bright rainbow ice cubes, so we can't list them all. Some of the best are practically flavorless, including saffron for a rich yellow, blue spirulina for a blue-green color, or"

Attempts to make colored ice cubes often produce a concentrated colored core surrounded by bubbly, cloudy ice. Some food colorings contain propylene glycol, a food-safe anti-freeze and emulsifier that can prevent or delay the coloring from freezing. Water freezes from the edges and surfaces inward rather than uniformly, which pushes impurities and dissolved additives toward the center during freezing. That process causes minerals, air bubbles, and any nonfreezing colorants to collect in the middle, creating the described effect. Natural alternatives include fruit-infused water, herbal teas, edible flowers, saffron, and blue spirulina for color without synthetic additives.

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