The most common and most likely answer to this crossword clue is the 7 letter word BREWING
I've seen this crossword clue in The Sunday Telegraph
B
R
E
W
I
N
G
More clues leading to the result BREWING
Buddy explains!

The straight part
We know that "Developing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case developing = brewing.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BREWING mean?
BREWING verb- To make tea or coffee by mixing tea leaves or coffee beans with hot water.
- To heat wine, infusing it with spices; to mull.
- To make a hot soup by combining ingredients and boiling them in water.
- To make beer by steeping a starch source in water and fermenting the resulting sweet liquid with yeast.
- To foment or prepare, as by brewing
- To attend to the business, or go through the processes, of brewing or making beer.
- (of an unwelcome event) To be in a state of preparation; to be mixing, forming, or gathering.
- To boil or seethe; to cook.
- The production of alcoholic beverages, such as beer, by fermentation; the process of being brewed.
- The business or occupation of a brewer.
- The quantity of a brew made in a single batch.
- The forming of a storm or the gathering of clouds.