Maybe try a dash of vodka in there instead of milk? Granted, the article is talking about fried chicken, but the same theory applies to tempura or fritters if you've got any flour in there.
http://www.seriouseats.com/2015/07/four-...icken.html
HOW IT WORKS
Adding vodka to your marinade mixture helps create a crust that stays light and crunchy instead of heavy, greasy, or leathery. How does this work?
As chicken fries, liquid evaporates and the breading dehydrates. After that, proteins in the marinade and flour will set and start to brown, giving the crust flavor. The more surface area you have, the crunchier the crust and the more flavorful the bird.
Vodka helps in both of these realms. First, it's much more volatile than water (which is the main component of buttermilk, pickle juice, or pretty much any other fried chicken marinade you'll be using). As such, it evaporates much more rapidly and violently. This helps drive moisture off the crust of the chicken faster, while also creating bigger vapor bubbles, adding surface area to the crust. Both of these things mean crisper, lighter fried chicken.
Finally, vodka also inhibits gluten formation. Gluten is the protein network that is created when flour and water are combined. This is important for things like bread and pizza crust, where a stretchy, chewy structure is desirable, but for crisp crusts, you want to minimize gluten development.