Why Is My Pesto Bitter?

Written By Lewis Crutch


Have you made pesto following your usual method but found that it tastes slightly more bitter than usual? Are you left asking wondering why your pesto has turned bitter? Then let’s see if we can help!

Your pesto is bitter due to it being overprocessed in a food processor. If you break basil down too much, it can become bitter tasting. If you overwork olive oil, it can release polyphenols which are bitter tasting. It is likely to be a combination of these two ingredients.

What Causes Bitter Pesto?

Unfortunately, bitter pesto isn’t just caused by overprocessing the ingredients. There are several reasons why your pesto might have a bitter taste:

  • Olive Oil Quality – Unbelievably, top-quality olive oil can have bitter notes, especially if it’s extra-virgin. Before you make your pesto, add a drop of oil to a spoon and give it a taste. It’s not as disgusting as it may sound and is a great way to determine the bitterness of the olive oil.
  • Pine Nut Alternatives – If you opt for cheaper alternatives to pine nuts, such as almonds, these tend to have a stronger, more bitter flavour. Pine nuts are far more subtle in their flavour, which is why they are the go-to ingredient in pesto.
  • Old Pine Nuts – As pine nuts go beyond their best, the oils will turn rancid. When you make your pesto, you’ll release these rancid (and bitter) oils into your pesto mix. Don’t just toss an open bag of pine nuts back into the cupboard. Instead, keep them stored in an airtight container.
  • Bolted Basil – When basil goes to seed and then flowers, this is called bolting. If you have picked your own basil then avoid picking any that has bolted. The flavour will have degraded and taken on a bitter edge.
Why Does My Pesto Taste Like Grass?

Your pesto may taste like grass for two reasons. If you have used poor-quality basil that lacks flavour, then it will be like using any green leaves. The other cause is if you have used too little oil, causing the basil to bruise and lose its flavour when processing.

Why is my Pesto Bitter

How to Fix Bitter Pesto

If you’ve already got bitter pesto, all is not lost. There are a few ways you can fix it. Work your way through this list and apply any fixes that apply to your particular problem pesto:

  • Add Lemon Juice – Adding an acidic element to pesto can balance the bitter flavour. The easiest way to do this is to add a squeeze of lemon juice. Remember to taste it regularly to avoid adding too much acid. You’ll also need to use the pesto quickly as the acid can discolour it, turning it a shade of brown.
  • Go Bold with the Flavours – Overpower the bitterness by adding strong flavours. Don’t hold back on the cheese. Add in a crushed garlic clove or mix in some crushed chilli flakes. Strong flavours should be able to mask any bitterness if you use enough of them.
  • Add Salt – You might think salt would make the bitterness worse, but a pinch of salt can help balance the bitter flavour. As with any additions, try adding a small amount, taste then repeat. You can always add a little more salt, but once it’s in, you won’t be able to remove it.
  • Make a Mini Batch and Combine – If you have got it horribly wrong, then don’t panic yet. Instead, try making a new small-batch using the tips above and then combine this with your bitter pesto. The new batch can help balance out the flavour of the rancid pesto.
  • Go Manual – If you haven’t made it yet, then opt for the manual approach. The food processor can be too excessive for breaking down basil leaves and nuts. Instead, try using a pestle and mortar where you have far more control over how much the ingredients are processed.

How Not to Fix Bitter Pesto

Before you panic trying to fix your bitter pesto and to avoid making the same mistake again and again, here are a few things you really ought to avoid doing when putting together your own pesto:

  • More Blending – As you know, overworking the ingredients may have been the cause of the rancid taste in the first place. Reaching for the on button and further blitzing it will only release more bitter oils.
  • Adding Oil – Your olive oil may be the cause of the bitterness. Before adding more oil, make sure you give it a taste to see if that’s why it tastes off in the first place.
  • Using Sugar – You might think sugar is an easy way to fix bitterness. However, this is unlikely to work. Instead, you’ll have instant sweetness followed by bitterness. Instead, try adding acid over sweetness.

Our Ultimate Basil Pesto Recipe

Although making pesto can be simple, if you don’t get your ratios right or if you tweak it too much, then you’ll end up with acrid, tangy pesto that no one wants to eat. Instead, use our ultimate pesto recipe:

Bitter Pesto FAQs

If you’ve still got more questions about bitter pesto, then these additional FAQs might help you out:

Should You Add Sugar to Bitter Pesto?

No, adding sugar will not fix bitter pesto. You might think that adding a sweet element to a bitter pesto will balance out that bitterness. This is not the case. What will happen is your pesto will taste sweet on the tongue initially before turning bitter.

Can You Make Pesto With Bitter Basil?

Basil will have a natural bitterness, but if you try it and it tastes more bitter than usual, then we would avoid using it in a raw sauce such as pesto and instead use it cooked in tomato sauces or soups where the bitterness will mellow.

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