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https://www.crystalpharmatech.com/fun-sharing-the-story-of-ice-crystals-and-frozen-foods-part-2.html
For the growth of large ice crystals in a case of frozen food, there is a very important influencing factor - the rate of cooling. When slow cooling, because of the long time to cool down to below the freezing point of water in the food, the initial water molecules form nuclei that are easily dispersed by the thermal movement of other water molecules, resulting in a reduction in the number of stable nuclei formed. At the same time the long cooling process gives water molecules sufficient time to focus on the combination of a small number of stable nuclei, and so grew into large ice crystals; and when rapidly cooled, because the temperature quickly dropped to a supercooling temperature, immediately formed a large number of stable nuclei. At the same time, the water molecules do not have sufficient time to collect, so they can only be scattered to each stable nucleus, forming numerous small ice crystals.