The behavior you described with almond milk freezing while cow's milk does not in a very full refrigerator is due to the differences in their compositions and properties.
Differences in Composition: Almond milk and cow's milk have different ingredients and compositions. Cow's milk is primarily composed of water, lactose (milk sugar), proteins, fats, and minerals. Almond milk, on the other hand, is made from almonds and water, often with added sweeteners, thickeners, and stabilizers.
Fat Content: One of the key differences is the fat content. Cow's milk contains more fat than almond milk. Fats have a higher freezing point compared to water, which is the dominant component in both types of milk. Because almond milk has a lower fat content, it is more susceptible to freezing at higher temperatures.
Emulsifiers and Stabilizers: Cow's milk naturally contains emulsifiers that help keep fat and water mixed together. These emulsifiers contribute to a smoother texture and can prevent milk from freezing as solidly as almond milk. Many commercially produced almond milks also contain stabilizers to enhance their texture, but these stabilizers might not be as effective in preventing freezing as the natural emulsifiers in cow's milk.
Protein Content: Cow's milk has a higher protein content compared to almond milk. Proteins can interfere with ice crystal formation and, to some extent, prevent the milk from freezing as solidly. The lower protein content in almond milk may contribute to its easier freezing.
When the refrigerator is very full, it can get colder due to restricted airflow and inadequate heat dissipation. This increased coldness might lead to almond milk reaching its freezing point and forming ice crystals more readily than cow's milk.
If you want to prevent almond milk from freezing, try storing it in a less-cold section of the refrigerator or away from the back wall where temperatures can drop significantly. Additionally, you can experiment with different brands of almond milk, as some might have different formulations that affect their freezing behavior.