The short answer
Yes, avocado pesto will turn brown relatively quickly after being made. This is due to oxidation of the avocado. However, there are several ways to prevent or slow down the browning process. The keys are minimizing exposure to air and acidifying the pesto. Adding lemon or lime juice to the pesto helps slow down browning. Storing the pesto with plastic wrap directly on the surface also prevents oxidation. Avocado pesto can be made in advance and kept refrigerated for up to 3 days before browning becomes noticeable.
Examining the causes of browning
Avocados brown quickly when exposed to air due to oxidation reactions. Oxidation causes the green chlorophyll pigments in avocado flesh to break down into brown pigments called melanoidins. Enzymes called polyphenol oxidases catalyze these browning reactions in avocados. When cells are damaged, such as when you cut or mash an avocado, these enzymes come into contact with phenolic compounds like chlorophyll and initiate the browning reactions.
Why traditional pesto doesn’t brown
Traditional pesto made with basil, pine nuts, parmesan, garlic, and olive oil doesn’t experience the same rapid browning problem. Basil contains very minimal amounts of polyphenol oxidase enzymes. And many of the ingredients in pesto, including olive oil, garlic, and parmesan, are acidic, which helps to inactivate the enzymes that cause browning.
The high oxidation rate of avocados
Avocados are unique in their high oxidation rates compared to other fruits and vegetables. The high fat and protein content of avocados gives more readily oxidized substrates. And avocados contain very active polyphenol oxidase enzymes that rapidly catalyze these reactions when the cells are ruptured.
This quick browning is why many people rub lemon or lime juice on avocado halves before storing to help slow the enzymes. The citric acid helps to denature the enzymes.
Tips to prevent avocado pesto from browning
Because of the quick browning reactions, avocado pesto needs special treatment to maintain its bright green color and fresh flavor. Here are some tips:
Add acid
Adding an acidic ingredient like lemon or lime juice is one of the most effective ways to slow browning. The acid helps to inhibit the polyphenol oxidase enzymes. About 1 tablespoon of lemon or lime juice per avocado used in the pesto can significantly slow the browning reaction.
Minimize air exposure
Keeping the pesto away from oxygen is key. You can accomplish this by:
- Storing in an airtight container
- Spreading plastic wrap directly on the pesto surface before sealing the container
- Piping into small freezer bags, removing excess air, and sealing
Keep it cold
Storing the pesto in the refrigerator at 40°F or below will help slow the enzymatic browning reactions. The cooler temperature makes the enzymes less active.
Blanch before blending
Blanching the avocado by immersing it in boiling water for 1 minute helps denature the enzymes and slows browning. However, this can negatively affect the flavor and texture.
Add antioxidants
Ingredients like vitamin C and citric acid are antioxidants that can bind up the oxidizing enzymes and intermediate compounds formed during browning reactions. This halts the process. So vitamin C rich foods like pineapple or oranges can help control browning.
Process with acidified water
When blending or processing the avocados, using acidified water (water with lemon juice, vinegar, or citric acid added) prevents the enzymes from coming into contact with oxygen. This is more effective than adding the acid after blending.
How long does avocado pesto last before browning?
With proper storage techniques, avocado pesto can last 3-4 days in the refrigerator before significant browning occurs. Here’s a timeline:
After making:
If exposed to air, oxidation will start immediately, and browning become noticeable in 30 minutes to 1 hour.
With air minimized, browning can take 2-3 hours at room temperature.
1 day:
Stored in an airtight container in the refrigerator, only minimal browning will occur after 24 hours.
3-4 days:
After 3-4 days in the fridge, browning will become more noticeable but the pesto is still usable if stirred.
1 week:
After 1 week refrigerated, oxidation reactions cause significant browning, off-flavors, and the pesto should be discarded.
Can you freeze avocado pesto?
Avocado pesto can be frozen for longer term storage. Freezing stops the enzymatic browning reactions that occur at warmer temperatures. To freeze:
- Fill ice cube trays with pesto and freeze.
- Transfer frozen pesto cubes to freezer bags.
- Freeze bags flat to minimize air exposure.
- Label bags with date.
Properly frozen pesto cubes maintain quality for about 3 months before flavor and texture degradation occurs.
Thaw cubes overnight in the refrigerator or for a few seconds in the microwave before use.
Avocado pesto recipe
Here is a simple avocado pesto recipe. The lime juice and refrigerated storage helps prevent browning.
Ingredients:
- 2 medium avocados, pitted and peeled
- 1 cup fresh basil leaves
- 1/4 cup olive oil
- 2 Tbsp pine nuts
- 2 garlic cloves
- 1/4 cup parmesan cheese
- 2 Tbsp lime juice
- Salt and pepper to taste
Instructions:
- In a food processor, combine the avocados, basil, olive oil, pine nuts, garlic, parmesan, and lime juice.
- Process until smooth, scraping down sides as needed.
- Season to taste with salt and pepper.
- Transfer to an airtight container, smooth the surface, and press plastic wrap directly onto the pesto.
- Refrigerate for up to 4 days.
Uses for avocado pesto
The creamy, fresh flavor of avocado pesto pairs well with:
- Bruschetta
- Pasta
- Sandwiches
- Pizza
- Salads
- Wraps
- As a burger topping
It can also be used:
- As a dip for bread, crackers, and vegetables
- Spread on sandwiches and paninis
- As a sauce over chicken, fish, shrimp, or vegetables
- Stirred into rice, quinoa, or couscous
Nutrition information
Avocado pesto is a nutritious spread and sauce. Here is the nutrition data for a 2 tablespoon serving (28g) of the pesto recipe above:
| Nutrient | Amount |
|---|---|
| Calories | 108 |
| Total Fat | 10 g |
| Saturated Fat | 1.5 g |
| Sodium | 74 mg |
| Carbohydrates | 2 g |
| Fiber | 1 g |
| Sugars | 0.5 g |
| Protein | 1 g |
Key nutrients:
- Healthy monounsaturated fats from the avocado oil
- Vitamin C, vitamin K, and folate from the avocado
- Calcium from the parmesan
- Phytonutrients like beta-carotene in the basil
Avocado pesto makes a great addition to a healthy diet given its nutritional profile.
Conclusion
In summary, avocado pesto does tend to brown relatively quickly compared to traditional pesto due to the high oxidation rate of avocado flesh. Proper storage techniques like refrigeration, airtight containers, plastic wrap, and freezing enable the pesto to maintain its bright green color and fresh flavor for days to weeks. The use of acid ingredients also helps stabilize the color by inhibiting the enzymes responsible for browning reactions. Avocado pesto is a delicious and nutritious spread that pairs well with breads, sandwiches, pasta, pizza, meats, and vegetables. With proper handling, you can enjoy its signature flavor and richness for several days after making it.