Pesto: Ingredients, Uses, Shelf Life, Contamination, and More

Pesto is for pasta, but that's not all.  It can go on chicken, in soup, in eggs, and on many other foods that need a lift.  Supermarkets usually carry both the traditional green pesto and the red tomato pesto. Therefore, you get to use the commercial type if you don't have the time or inclination to make your own. Like salsa, pesto is a versatile flavor enhancer.  If you're unfamiliar with it and have a tendency to shy away from the unknown, read on as Shelf Life Advice gives you the lowdown on a sophisticated, exotic, and quite delicious taste treat. 

What makes pesto pesto?

Traditional pesto is a green sauce. Here's how food scientist Dr. Karin Allen describes it: "From a classic culinary perspective, pesto contains basil, olive oil, pine nuts, garlic, cheese, and salt."  Some online recipes say either pine nuts or walnuts will do.  The cheese is usually either Romano or Parmesan. However, the pesto chef can add or substitute whatever he/she wants to give the sauce an ethnic flavor or to use up whatever happens to be in the fridge.  For example, website contributors have mentioned using mint, parsley, spinach, feta cheese, roasted (rather than fresh) garlic, and pepper.  The Chicago Tribune says almost any fresh herb will do, but strongly-flavored ones--such as sage, thyme, or oregano--should be used sparingly.  Also, the same article gives you permission to use any hard cheese and any kind of nut you like.

Where did pesto originate? 

The traditional version, commonly labeled "pesto genovese," comes from Genoa, the Liguria region of northern Italy, Wikipedia says. But the online encyclopedia also tells us that the ancient Romans ate a somewhat similar paste made by crushing cheese, garlic, and herbs together. Basil, the main ingredient of the most common pesto, probably originated in India. The French version--first created in Provence--includes parsley and excludes pine nuts because the latter don't grow in Provence.

Is the name "pesto" Italian?

Yes, says Wikipedia. "Pesto" comes from an Italian word meaning "to pound or crush."  That's because, using the traditional method, some of the ingredients are ground up using a marble mortar and wooden pestle.  Nowadays, pesto chefs are more likely to get out their food processor or blender.

Outside of Italy, the name "pesto" is sometimes applied to cold sauces that have none of the ingredients Americans commonly associate with pesto. 

What foods besides pasta does pesto go well with?

Wikipedia mentions minestrone, boiled potatoes, and tomatoes.  It's also tasty mixed with green beans and mushrooms.  Online, there are also several chicken breast recipes using pesto.  (To see one, go to kalynskitchen.com, "Easy Recipe for Baked Chicken.")

Is it best to buy pesto or make your own?

It's not challenging or time-consuming to make.  (Online recipes say you can do it in 15-10 minutes.) When looking for a recipe online, read the comments/reviews.  Those who have tried it will tell you if it's good, if it contains too much garlic, etc.  One online recipe that got rave reviews is on Allrecipes.com on the pesto sauce page.  It is made with walnuts instead of pine nuts and uses Parmesan cheese rather than Romano.

For those trying to avoid processed food, it's good to know that homemade pesto is not time-consuming to produce. But, let's face it, it's even faster to open a jar.  Moreover, the jarred product may have the benefit of ingredients and processing techniques that help the sauce last longer and remain safer than the homemade product. (More about shelf life and contamination in the Q/As below.)  You can buy small jars of pesto for about $3.00.

What's the shelf life of pesto?

Keep in mind that the term "shelf life" refers to the time when a product begins to spoil.  (It's no longer at its best; it may start to taste, look, or smell bad.)  It is not about the time when a food begins to develop pathogens that can make a person sick. In general, the shelf life of pesto is rather short.  Homemade, figure a week.  Store-bought, once opened, figure a couple of weeks.   But it can be frozen for long-term storage. 

For specific information about the shelf life of various versions of this product, consult the handy chart on this page.  It lists both commercial and homemade pesto, unopened and opened, taken from a can or prepared from a dry mix.  Note that, unless it's frozen, we're talking a few weeks at most.

Pesto should be refrigerated in an air-tight container. The article "Does pesto go bad?" offers this tip: "To boost the 'shelf- life' of the pesto in the fridge, make sure that it is completely covered with olive oil before sealing the container." The layer of oil makes the pesto anoxic, but there's still no danger of botulinum growth if the product is kept refrigerated at a proper temperature.

How can you tell when pesto has gone bad?  The website eatbydate.com offers this advice: Once the oil or the basil leaves change color (start turning brown), the flavor is affected, and the pesto is not good to eat.

The pesto jars that I purchased at a local grocery store (two different brands) were made in Italy and had no use-by date on them.  The chart referred to above says unopened canned pesto lasts 4-6 weeks, so I'll follow that advice and not keep it too long.

When asked about the shelf life of an open jar of pesto, food process engineer Dr. Timothy Bowser said, "I think one to two weeks should be no problem for a standard pesto sauce and perhaps 4 to 6 weeks for an acidified pesto."

Pesto freezes well, so the shelf life can be extended to 3-4 months by proper freezing.

What should pesto lovers know about spoilage and contamination?

Online discussions of pesto generally talk about the risk of its developing dangerous pathogens, especially those that can cause botulism. Since garlic bulbs (one of the main ingredients of pesto) grow underground, there is a risk of serious illness from botulinum spores. However, the following comments from Shelf Life Advice Advisory Board scientists are reassuring:

Food scientist Dr. Karin Allen: "Commercially canned or bottled pesto from the store shelf has been heat treated to destroy C. botulinum spores. After you open it, it should be refrigerated to prevent spoilage, but it isn’t necessarily a safety concern.  If you purchase refrigerated pesto (or make your own), it should remain refrigerated. This is adequate to prevent C. botulinum spores from “waking up,” but spoilage bacteria/mold can still grow. For a longer shelf life, it can be frozen." 

Food scientist Dr. Clair Hicks: "C. botulinum does not grow at refrigeration temperatures and can not produce toxin at that temperature.  What can grow at refrigeration temperatures are the psychrotrophics, the most common of which are Pseudomonas and Bacillus. These are not pathogens, but they do make the food taste bad. The growth of these takes about two weeks.  The only pathogen that can grow slowly at refrigeration temperatures is Listeria. However, if the pesto was heated to 165°F during preparation, this would never be a problem.  If not heat treated, this pathogen could be a problem. If fresh pesto is heat treated, packed in a MAP package, and refrigerated, it will be good for 20 days.  Only after opening would it go bad faster.   I would also think most fresh pesto would be formulated with acid or mold inhibitors."

Dr. Timothy Bowser [when asked if there was a risk of botulinum spores]: "Yes, for the low- acid, traditional pesto sauces. The high-acid versions would preclude the growth of botulinum."

What processes are used to produce commercial pesto?

Dr. Tim Bowser provided this description: "Hot packing is a method for heat treating high-acid foods. The product is heated to about 195°F and put into the jar. Another method would be to put the product into a jar at room temperature and then place it in a hot-water bath. The pesto must be acidified (with vinegar or acetic acid for example) to hot pack or water bath. Many people don’t like acidified pesto. Some might say that it is not actually a pesto, but the definition of pesto is open to interpretation.  Commercial pesto is normally retorted (pressure cooked) to kill bacteria, unless it is a high-acid product, which can be hot-packed or water-bathed." 

What are some tips for freezing pesto?

1. If you're making your own, don't add the cheese before freezing.  Add the cheese after the pesto is defrosted. Some sources say that the cheese does not freeze well.  

2. The website Simplyrecipes.com recommends freezing pesto in an ice cube tray. First, line the tray with plastic wrap; then fill each pocket with pesto.  After it's frozen solid, remove the pesto from the tray and store it in a freezer bag.  Add grated Parmesan or Romano cheese after defrosting. See "Fresh Basil Pesto" for another recipe.

3. Another recommendation, submitted by a reader of simplyrecipes.com, is to freeze just the leaves and olive oil (processed together) rather flat in a freezer bag. Then, when fresh basil is out of season, break up the frozen stuff into a bowl, defrost, and add the rest of your pesto ingredients. 

4. Eatbydate.com recommends defrosting pesto by placing the packaged pesto in a bowl of cold water or by placing it overnight in the fridge. 

Source(s):

Karin E. Allen, Ph.D., Utah State University, Dept. of Nutrition, Dietetics, and Food Sciences

Timothy J. Bowser, Ph.D., Oklahoma State University, Dept. of Biosystems and Agricultural Engineering

Clair L. Hicks, Ph.D., University of Kentucky, Dept. of Animal and Food Sciences

eatbydate.com "The Shelf Life of Pesto"

http://www.eatbydate.com/pesto/

allrecipes.com "Pesto Sauce" 

http://allrecipes.com/recipe/pesto-sauce/

cooking.stackexchange.com "Does Pesto Go Bad?" 

http://cooking.stackexchange.com/questions/16609/does-pesto-go-bad

simplyrecipes.com "Fresh Basic Pesto"

http://www.simplyrecipes.com/recipes/fresh_basil_pesto/