To slowly trickle some kind of liquid into something. A noun or pronoun can be used between "drip" and "in." Just drip the food coloring in so that you don't add too much of it. I dripped in the melted butter a little bit at a time, until it was emulsified with the egg yolks completely.
drip in(to) (something)
1. To slowly trickle into something, as of a liquid. There must be something wrong with the faucet because water is still dripping into the sink.
2. To slowly trickle something into something. Just drip the food coloring into the cake batter so that you don't add too much of it.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
(to something ) [for a liquid] to fall into something drop by drop. The water dripped into the bowl we had put under the leak. Is the water still dripping in the bathtub?
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.