I have a question about the recipe "Peruvian Shrimp Ceviche (Sivinche)" from Food52. What "cooks" the shrimp in this recipe? Traditionally, it's a citric acid, but I don't see anything like that here.
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The red wine vinegar (and to a lesser extent the tomatoes) provide the acidity that denatures the shrimp; lemon juice is used in traditional ceviche recipes.
Here's is a table of pH values for a small selection of items:
Lemon juice and vinegar both have a pH of 2. While whole tomatoes are not listed in this table, tomato juice clocks in with a pH of 4.