How can you tell if pesto sauce is bad?

Answer 1

If it is kept around long enough and not handled properly, Pesto can spoil. The fats and oils (pine nuts, cheese, olive oil) can become rancid. If not stored cold enough, there is the possibility that it could grow Clostridium botulinum.

Answer 2

No.

In fact, pesto can be really good for you.

The one caveat to be concerned about is the hard cheese you might add. Pesto is traditionally made with pecorino Romano or Tuscano and Parmesan.

You can leave out the cheese and still create a very delectable pesto.

In fact, vegans always do that.

A vegan pesto might incorporate miso or a yeast based Parmesan-cheese flavored substitute.

Creamy pestos also sometimes incorporate some dairy like ricotta or soft swiss chese. A vegan pesto can be made creamy, however, with soft, ripe avocado or soft tofu.

Concerning the other ingredients:

Basil is a carminative and contains antioxidants.

Olive oil is an awesome source of monounsaturated fat.

Garlic is good for our heart and over-all circulation

Pine nuts are a tasty source of non-meat protein and a source of antioxidants in their own right.