First, let's isolate the conditional clause.
"If left to stand, cooked pasta sticks together."
"If left to stand" is written in the simple past tense (or, just past, if you will). The key word is "left", which is the past tense of "leave", which makes it a Type 2.
If the sentence were written "If you leave it standing, the cooked pasta will stick together" (just for the sake of example), then you would be dealing with a Type 1 conditional clause, which anticipates a future event in the case that a certain event happens. Type 2 conditional clauses discuss an "imaginary circumstance" that would happen - but, most likely won't.
If the tone of the sentence was regretful, like:
"If it hadn't been left to stand, the cooked pasta wouldn't have stuck together."
then, we would have a Type 3 clause, where the statement looks back at a past event that, if changed, could have determined a different outcome.
Hope this helped!