How to Make Mayo from a Jar of Leftover Oil (Yes, Really!)

gratefulheartcolle
May 31
3 min read

Let’s talk Mom Magic. You know—that ability to see what everyone else would toss out… and turn it into something amazing.

Ever finish off a jar of pickled hot mushrooms (or artichokes, or sun-dried tomatoes) and stare at that leftover oil thinking, “This has to be good for something, right?”

Friend, it is. ✨Let me show you how to turn that flavorful, herby oil into the most delicious homemade mayo—right in the original jar. No waste. No fancy equipment. Just real food and a little kitchen know-how.

🧄 Why It Works

That leftover oil is loaded with flavor—garlic, chili flakes, herbs, even brine. It’s already infused, seasoned, and begging to be transformed. Mayo is basically just an emulsion of oil, egg, and acid (like lemon juice or vinegar), which means that funky jar of leftovers? It’s actually gold.

🥄 What You’ll Need

1 egg (room temperature is best)
1 tablespoon lemon juice or white vinegar
1 teaspoon Dijon mustard (optional, but helps with emulsifying)
Salt, to taste (you probably won’t need much!)
About 1 cup of leftover seasoned oil
Immersion blender (or a regular blender if you prefer)

🥣 How to Make It – Right in the Jar

Grab your jar – the one that had the hot mushrooms (or whatever you just finished eating). Make sure it’s clean-ish—a few bits of seasoning left behind are perfect.
Crack in the egg. You want the whole egg—yolk and white.
Add your lemon juice and optional mustard. This is what helps emulsify and gives it that tangy mayo taste.
Place the immersion blender all the way at the bottom of the jar and start blending on high. You’ll see it transform almost instantly!
Slowly lift the blender as the mixture thickens and turns into creamy, dreamy mayonnaise.
Taste and adjust. Add a pinch of salt, more lemon, or even a clove of garlic if you’re feeling bold.

🧺 Why I Love This Hack

✅ Reduces waste
✅ Makes the most of your groceries
✅ Saves money (have you seen the price of fancy mayo lately?)
✅ Makes your sandwiches, devilled eggs, and potato salads taste gourmet

Want a printable PDF of the full recipe?

FREE Printable Recipe!

🧠 Pro Tip

If your oil has strong flavors (like chili or garlic), your mayo will too! If it’s super intense, you can always do half seasoned oil, half neutral oil to mellow it out.

Note: If your homemade mayo turns out too thin, here are the best ways to thicken it naturally and effectively:

✅ 1. Add More Egg Yolk (or Just Yolk Next Time)

Best method if your mayo is runny from the start.

How: Start a fresh bowl with a new egg yolk, then slowly whisk in the thin mayo a bit at a time.
Why it works: The lecithin in egg yolk is a natural emulsifier and helps stabilize and thicken the mixture.

✅ 2. Slowly Add More Oil

Best if the mayo is slightly too thin.

How: Continue to whisk (or blend) while very slowly drizzling in more oil. Go slow!
Why it works: Mayo thickens as more oil is emulsified. Going too fast will break the emulsion instead.

✅ 3. Use an Immersion Blender

Best tool to fix or thicken mayo quickly.

How: Blend from the bottom up, moving slowly. If you're using seasoned oil (like from a jar of mushrooms), make sure it’s not too hot.
Why it works: The high-speed blending helps re-emulsify and thicken the mixture better than hand-whisking alone.

✅ 4. Add a Thickener (as a last resort)

If the emulsion is stable but still too loose:

Options:
- ½ tsp xanthan gum
- ½ tsp mustard powder (adds both flavor and thickening)
- A small spoon of potato starch or cornstarch slurry (cook first if needed)

Be careful – too much can affect the texture or taste.

🛑 Avoid:

Adding water or watery ingredients (like vinegar or lemon juice) after emulsification unless balancing with more yolk or oil.
Using only egg whites — they don't emulsify mayo well on their own.

Check out the full video showing how I prepare this super tasty spread below!

📸 Show Me Yours!

If you try this trick, tag me @gratefulheartcollective on Instagram—I love seeing your creative kitchen wins. And if you’ve got other “leftover jar” ideas, drop them in the comments. Let’s keep saving money and making magic together. 💛

xoxo Chelsea Dyan