I'm a librarian who loves anime, manga, and reading a wide variety of genres.
In my experience, cozy mysteries that have a food or crafting theme will often include recipes or projects. This one sort of does a similar thing, except it's incorporated directly into the text. Clare has just walked off to make some coffee for one of the detectives investigating the attack at her coffeehouse, and readers are now being treated to multi-step advice on how to store coffee. Earlier, it was instructions on how to make a perfect cup of coffee (with a coffee press or something? I admit that I wasn't paying a lot of attention).
I still feel like the attack isn't getting enough weight. It feels like coffee, the coffeehouse, and even the stupid 100-year-old plaque (supposedly the coffeehouse's only signage, and worth nearly $1000) are all more important than the attack.