I tend to judge "purpleness" of prose not based on length, but on necessity.
Purple prose is redundant. It draws attention to the prose, in a bad way that draws attention away from the thing that you want to describe.
For example, here's a paragraph from Stephanie Meyer (one of the Twilight books) that reads to me as purple prose:
The sky above me was clear, brilliant with stars, glowing blue in some places, yellow in others. The stars created majestic, swirling shapes against the black universe-an awesome sight. Exquisitely beautiful.
.
It's a short paragraph, but it feels overly descriptive. And I think that the last sentence is what pushes it over the top. "Exquisitely beautiful--" only two words, yet so unnecessary. If you as a writer have done an adequate job of describing the scene in a way that effectively conveys its exquisite beauty, you won't need to end the paragraph with a sentence that explicitly TELLS me that it was "exquisitely beautiful."
This is just my opinion, but I suspect that others share it. Just because a paragraph (or sentence) is short doesn't mean that it isn't purple. "Bob was a stout and fat man" may be a short sentence, but you can remove one of the adjectives to make it shorter without losing any meaning.
I always look for repetition in word choice, because I feel it really tends to break word flow. But I also look for redundancy in meaning. Are you using unnecessary sentences that convey information already included in the sentence that immediately proceeds or follows them? For example:
Brendan was a fast runner. Whenever we went to track meets, people were always impressed by his speed.
But suppose we just read it like this:
Whenever we went to track meets, people were always impressed by Brendan's speed.
The first sentence, "Brendan was a fast runner," is completely unnecessary, because the other sentence is already telling us that he's a fast runner, and conveying quite a bit more information as well (namely, that he competed in track meets, and that other people were impressed by the extent to which he was a fast runner). "Brendan was a fast runner" is redundant and worthy of removal.
Now, to reference an example from earlier in this thread:
A "Bacon and cheese? Sounds like a combination for a heart attack."
B "Really? I've been having this for the past 10 years of my life already! Doesn't seem to do me any harm!"
A "Have you checked this with your doctor recently?"
Vs.
A "Bacon and cheese? Sounds like a combination for a heart attack."
B "Really? I've been having this for the past 10 years of my life already! Doesn't seem to do me any harm!"
"A turned to B slowly as he continued to chop the garlic, blinking at him with a questioning gaze."
A "Have you checked this with your doctor recently?"
That "extra line" is not redundant in any way. It gives us new information that wasn't there before it was added. It actually helps to contextualize the line after it. When A says "Have you checked with your doctor recently?" the reader is better able to visualize the delivery, because the line that describes his questioning gaze gives us a better idea of exactly how A is reacting to B. I would keep this line in. I like to include lots of beats in my stories.
Having "extra" lines that state information that we already knew is purple. Having "extra" lines that provide additional context for what is going on can be quite helpful. Adding lines to provide context can help increase the reader's focus and attention on the parts that you want them to pay attention to. I think the place where you cross a line is when you provide so much "context" that it
distracts the reader from the parts you want them to pay attention to. And that can vary from scene to scene.
In this dialog scene, think about what's important. Why is the scene here? Is it to inform the reader of one of the character's eating habits? Or is it there to establish the rapport that exists between two characters? Which of these two things is the focus? For example, suppose the important part of this scene is "these are two characters the reader needs to get to know, the reader needs to understand their behavior patterns and speech patterns and understand what kind of relationship they have with each other. If that's our focus, then the lines that add little details like what kind of facial expressions the characters make when reacting to each other can be
immensely important.
The opposite of purple prose is often describe as "Orwellian prose," and if you want to get a good understanding of Orwellian prose you can read George Orwell's essay "Politics and the English Language," or pick up one of his books. "Orwellian prose" is designed to be minimalist and not draw attention to itself.
If prose is a windowpane through which we see a story, Orwell's goal was for that windowpane to be as clear and transparent as possible. You don't want to see the window itself; you want to see the beautiful thing that is on the other side of the window.
Except, sometimes you don't want to use the windowpane as something to look through. Sometimes, you just want to look at a beautiful stained-glass window. For example, the form of poetry is based around the idea of creating prose that is beautiful in and of itself. Like purple prose, this sort of prose draws attention to itself, but it draws attention to itself intentionally. Sometimes, you want to literally write poetry. (And I'm not talking about poetry that's just defined by its rhyming scheme.)
Sometimes, an author will describe a destitute man on the street, and use a metaphor to describe his situation, comparing the man on the street to a man drowning the ocean, completely at the mercy of his circumstances. But sometimes, the metaphor becomes this long and drawn-out thing, where the author continues to describe the waves crashing against the man, and the cruelty of the salty air that chokes his ability to breathe even in the brief moments that his head pierces the surf, and after several sentences you've completely forgotten about the homeless man begging on the street because the image of the man being tossed about by the waves is so vivid that it completely drowns everything else. This is not a
bad thing. Sometimes, as an author, you want to make something weird and artistic that draws people's attention away from the concrete and into the world of metaphor, but it's not the kind of thing you want to do by accident.
For an explicit example, read this chapter of
Victor Hugo's Les Miserables, "Billows and Shadows". Out of context, you might think that it's a 750-word description of a man drowning, struggling until he is swallowed up by the sea. But it's not actually about a drowning man. It's a metaphor for the plight of ex-convicts in 19th century France. It's actually quite beautiful, but while this metaphor is being laid upon the reader, our attention is briefly taken away from the main character of the story and exactly what was happening to him when this digression happened. It's not purple; it's poetic.