Why is my pesto bitter?

Discover the surprising culprit behind that pesky bitter taste in your pesto and how to fix it quickly.

I have to admit, my pesto is not always perfect and sometimes I can make several mistakes. That is why, some of these times, the pesto can turn out bitter, which can be disappointing and ruin the dish. That is why I have written this post to help you (mostly help myself :)) find out where the bitterness comes from.

So if you’ve ever found yourself wondering, “Why is my pesto bitter?”, you’re not alone. Here, we’ll explore the common causes of bitter pesto and provide some tips for fixing it.

Table of Contents

    Common causes of bitter pesto:

    There are several factors that can contribute to the bitterness of pesto. Here are a few common causes:

    Mature/flowering basil

    It is possible for matured or flowering basil to contribute to bitterness in pesto. As basil plants mature, they produce flowers, and the chemical compounds in the flowers can contribute to bitterness in the leaves. This is because the flowers contain a chemical compound called eugenol, which can have a bitter taste.

    The nuts

    Bitterness in pesto can sometimes come from the nuts, rather than the basil. Nuts contain a substance called tannin, which can contribute to bitterness when it is present in high amounts.

    Tannin is usually found in the skin surrounding nutmeats, and removing as much of this skin as possible can help to eliminate bitterness in the final product. Walnuts, in particular, can be a challenge to de-skin, as the skins can be difficult to remove completely.

    Using cheap or stale walnuts can also contribute to bitterness, as these nuts may contain higher amounts of tannin or may be more prone to becoming rancid. To prevent bitterness in your pesto, using fresh, high-quality nuts and removing as much of the skin as possible is important.

    Using cheap oil

    Using cheap or low-quality oil can potentially contribute to bitterness in pesto. Oil is an important ingredient in pesto, as it helps to emulsify the mixture and give it a smooth, creamy texture.

    However, the type and quality of oil you use can affect the flavor of the final product. Cheap or low-quality oils may not have as robust a flavor as higher-quality oils, and they may also contain impurities or contaminants that can contribute to bitterness. Therefore, it is generally recommended to use a high-quality, flavorful oil in pesto, such as extra virgin olive oil.

    This will help to give the pesto a rich, balanced flavor and help to prevent bitterness. It is also important to store your oil properly to prevent it from becoming rancid, as rancid oil can also contribute to bitterness.

    The garlic

    Sometimes, garlic can sometimes contribute to a bitter taste in pesto when it is processed in a food processor or blender. To avoid this, you can try omitting the garlic from the pesto recipe and instead dicing it by hand or mashing it in a mortar and pestle.

    You can then stir the garlic into the pesto at the end after all the other ingredients have been combined. This can help to preserve the flavor and prevent bitterness.

    How to fix bitter pesto

    If you love the fresh, herby flavor of pesto but have struggled with bitterness, don’t worry! With a few simple adjustments and some careful ingredient selection, you can enjoy delicious, non-bitter pesto every time. Here are a few things you can try to fix it:

    Add sweetness

    If your pesto is too bitter, adding a small amount of sweetness will most certainly balance out the flavor. This can be something like a teaspoon of honey or a small amount of grated Parmesan cheese(if in this case, you are not making the original pesto ala Genovese).

    A pinch of sugar or a squeeze of lemon juice will also suffice. These ingredients can help to balance out the bitterness and add a touch of sweetness or acidity to the pesto.

    I can guarantee you that a few drops of lemon juice will absolutely not change the final taste, but rather, will help you avoid the dark color and bitter taste. Just be careful not to overdo it – a little bit goes a long way.

    Blanch the basil

    Another little trick to prevent the pesto from blackening and becoming bitter is to blanch the basil leaves by immersing them in boiling water for 10 seconds and then for 1 minute in water and ice. The green will be super bright!

    Also read: Should you blanch basil for pesto?

    Use young basil leaves

    Use young, fresh basil leaves for pesto, rather than mature or flowering ones, in order to prevent bitterness. To prevent your basil plants from flowering, you can simply remove the buds before they open, which will also encourage the plants to become bushier. Using fresh, high-quality basil is key to achieving a flavorful and enjoyable pesto.

    Dilute the pesto with extra virgin olive oil or pasta cooking water:

    One option for fixing bitter pesto is to try diluting it with a little bit of extra virgin olive oil or with some pasta cooking water. This can help to balance out the bitterness and give the pesto a creamier texture. Just be careful not to add too much liquid, as this can dilute the flavor of the pesto.

    Store pesto properly

    It is generally true that homemade pesto has a shorter shelf life than store-bought pesto, simply because the latter contains preservatives. However, the flavor of this commercial (especially cheap) pesto can change over time, and the oils in the nuts and the basil can become rancid or oxidized, leading to a bitter or off-flavor.

    That is why it is a good idea to store your store-bought pesto a cool, dark area (preferably in the pantry) or in the refrigerator after it has been opened. Also, try to buy the smallest size available, as this will help you to use it up more quickly and prevent waste.

    For homemade pesto, you can prepare it in quantity and freeze it, or simply store it in the refrigerator. Just remember to cover the surface with a layer of oil once it has been poured into the jars. It will prevent it from oxidizing.

    Also read: Can you freeze pesto?

    Start from scratch

    In some cases, it may be necessary to start from scratch if your pesto is too bitter to salvage. This means using fresh, high-quality ingredients and carefully following the recipe to ensure that the pesto turns out flavorful and enjoyable.

    Related questions:

    What can I do if my pesto is too thick?

    What can I use as a substitute for pine nuts in pesto?

    Can I make pesto without a food processor or blender?

    Tasting each ingredient separately and uncooked can be a useful strategy for identifying the source of bitterness in pesto. By tasting each ingredient on its own, you can get a sense of which ingredients may be contributing to the bitterness and which ones are not.

    If none of the ingredients taste bitter when tasted separate, you can then start to combine them, adding one ingredient at a time and tasting the mixture after each addition.

    This can help you to identify which ingredient is causing the bitterness. Once you have identified the bitter ingredient, you can then consider substituting it with something else or adjusting the ratio of ingredients in the recipe.

    It’s important to keep in mind that a recipe is just a starting point, and you may need to make adjustments based on the specific ingredients you are using and your own personal taste preferences.


    Bitter pesto can be a frustrating experience, but with a little bit of knowledge and some careful ingredient selection, you can avoid it and enjoy delicious, flavorful pesto every time.

    Remember to use fresh, high-quality ingredients, be careful not to overprocess the basil, and measure the oil carefully to avoid bitterness. With these tips in mind, you’ll be able to enjoy pesto that is full of flavor and free from bitterness.

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