Onion Soup with Hemp Croutons: Recipe

Onion soup relies on one thing: patience. The onion must change color on its own, over low heat, for nearly forty minutes, and no shortcut can replace that. What can be changed without loss is the croutons. Bread cubes coated in hemp flour acquire a nutty flavor that balances the sweetness of caramelized onions and add protein and fiber, which are almost absent in the soup itself. Hemp flour is not ground grain, but a cake left after oil extraction from seeds: in a measurement published in the journal Foods, it had 31.62% protein and 43.76% fiber in dry matter. Below you have the proportions for four servings, the order of operations, and the places where this soup most often comes out flat.

KEY INFORMATION
• Hemp flour (Capcanari et al., Foods, 2023): 31.62% protein and 43.76% fiber in dry matter, compared to 12.45% and 1.51% in wheat flour.
• Caramelizing onions takes 35-40 minutes over low heat and cannot be shortened.
• Croutons made with hemp flour are baked at 180°C for 10-12 minutes.
• Without cheese and without wine, this soup is vegan and alcohol-free.

What does hemp flour add to the croutons?

Croutons in onion soup are primarily responsible for texture, while hemp flour adds flavor and composition. In a measurement published in the journal Foods, hemp seed cake contained 31.62% protein and 43.76% dietary fiber in dry matter, compared to 12.45% and 1.51% in wheat flour studied in the same work (Capcanari et al., 2023).

The difference comes from the production method. Hemp flour is not made from ground grain, but from the cake that remains after oil is pressed from the seeds. The fat leaves with the oil, while protein and fiber concentrate in the residue. Therefore, hemp flours from different producers can vary: the more thoroughly defatted the cake, the higher the protein content. The numbers above come from one sample of one cake, so read them as an order of magnitude.

Source: own elaboration based on Capcanari et al., Foods, 2023.

We have noticed in our own trials that hemp flour adheres to bread cubes without egg and without water: just drizzle them with oil and mix. Breadcrumbs in this role fall off onto the baking sheet, while hemp flour stays on the bread and bakes together with it. The nutty aroma appears about halfway through baking, and that is a good time to check the oven.

Why must caramelizing onions take 40 minutes?

Because the dark color and sweetness of the onion arise from two slow processes at once: the Maillard reactions between sugars and amino acids and the breakdown of the sugars themselves. Both processes are more complete the longer they occur at a moderate temperature. Turning up the heat does not shorten them; it only burns the onion on the outside before it has time to soften on the inside.

A practical marker is simple. After fifteen minutes, the onion is golden, soft, and quite tasty, but the soup made from it comes out flat and watery. Only after 35-40 minutes does the color turn dark amber, the volume decrease by more than half, and brown sediment appear at the bottom of the pot, which you dissolve with wine or broth. This sediment carries most of the flavor of the finished soup.

Incidentally, it is worth correcting the widespread notion that long cooking increases the quercetin content in onions. Heat treatment does not create this flavonoid; it only changes its form. In a study of roasting onion glycosides, quercetin at 180°C broke down to the aglycone quercetin, which remained stable with further heating (Rohn et al., 2007). Caramelization over low heat is different from roasting, so do not transfer this work directly to the pot. The conclusion that can be transferred is this: quercetin from onions withstands heating but does not multiply from it.

What do you need for onion soup with hemp croutons?

Proportions for four servings. Caramelizing the onions takes 35-40 minutes, cooking the soup another 15, and the croutons bake for 10-12 minutes simultaneously, so the whole process closes in one hour.

800 g onions, about four large ones
1 l beef or vegetable broth
3 tablespoons butter or coconut oil for caramelizing
2 cloves of garlic
100 ml dry white wine or a tablespoon of lemon juice with a tablespoon of apple cider vinegar
sprig of fresh thyme and bay leaf
teaspoon of sugar
salt and pepper to taste
4 thick slices of bread, wheat or gluten-free
2 tablespoons hemp flour and a tablespoon of oil for coating the croutons
optional: 60 g grated gruyère or parmesan for baking

Two shopping notes. Keep hemp flour in a closed container, in a cool place and away from light, as in the measurement cited above, the cake still had 8.19% fat, which determines how quickly the flour will go rancid. If you are making a gluten-free version, the label on the bread and flour packages decides: the implementing regulation of the Commission (EU) No. 828/2014 allows the use of the term ‘gluten-free’ only with a content of up to 20 mg of gluten per kilogram of the finished product. More about substitutes and proportions can be found in our guide on hemp flour in baking.

How to cook onion soup step by step?

Five tasks, one of which takes more time than all the others combined. There is about twenty minutes of active work here; the rest is done by low heat. Put the croutons in the oven when the onion starts to darken.

Caramelize the onion. Slice it into thin half-moons, heat fat in a wide pot over low heat, add onion, salt, and sugar. Stir every 3-4 minutes for 35-40 minutes until the color turns dark amber.
Prepare the hemp croutons. Cut bread into 2 cm cubes, mix hemp flour with oil and a pinch of salt, coat the cubes in this mixture and spread them on a baking sheet. Bake at 180°C for 10-12 minutes until crispy.
Build the soup. Add garlic to the caramelized onion and sauté for a minute. Pour in wine or a mixture of juice with vinegar and reduce for two minutes, scraping the sediment from the bottom. Add hot broth, thyme, and bay leaf, and simmer for 15 minutes over low heat.
Season. Remove thyme and bay leaf. The soup should be deeply sweet with a distinct umami note. Season with salt and pepper, and if the flavor is flat, add a teaspoon of soy sauce.
Serve with croutons. Pour the soup into bowls and place the hemp croutons on top. Optionally sprinkle with grated cheese and place under the grill for 2-3 minutes. Serve immediately while the croutons are crispy.

How to modify the recipe for diet and taste?

The base is resistant to modifications, as all the flavor is carried by the onion, not the additives. To make a vegan version, replace butter with oil or coconut oil, and beef broth with root vegetable broth; substitute the baking cheese with nutritional yeast, which provides a similar umami note. The croutons made with hemp flour are vegan by definition, as only oil is needed for coating.

The alcohol-free version is a tablespoon of lemon juice and a tablespoon of apple cider vinegar instead of wine. It is about acidity that cuts through the sweetness of the onion, not the alcohol itself, so the effect is similar. You can add a crushed clove of garlic to the mixture of hemp flour and oil, which will bake together with the bread at 180°C.

The biggest mistake with this soup is shortened caramelization, and the second in line is too thin broth, which dilutes everything the onion has managed to build. If you are looking for a quicker soup but still with a hemp accent, check out our recipe for tomato soup with hemp oil or broccoli cream soup with seeds.

Frequently Asked Questions

What does hemp flour add to the croutons for onion soup?

A nutty flavor that balances the sweetness of caramelized onions, as well as protein and fiber. In a measurement from the journal Foods, hemp seed cake contained 31.62% protein and 43.76% fiber in dry matter, compared to 12.45% and 1.51% in wheat flour (Capcanari et al., 2023).

How long does it take to caramelize onions?

From 35 to 40 minutes over low heat. After fifteen minutes, the onion is golden and soft, but the soup made from it comes out flat. The dark amber color, a reduction in volume of more than half, and brown sediment at the bottom of the pot only appear at the end of this time.

Are croutons made with hemp flour gluten-free?

Hemp flour itself does not contain gluten, as hemp is not a grain. The gluten-free status of the croutons depends on the bread used. For a gluten-free diet, use bread labeled ‘gluten-free’, which according to Regulation (EU) No. 828/2014 means a content of up to 20 mg of gluten per kilogram of the product.

What can replace wine in onion soup?

A tablespoon of lemon juice and a tablespoon of apple cider vinegar. The wine serves as an acid that cuts through the sweetness of the onion and helps to scrape the sediment from the bottom of the pot, so any other acid of similar strength will work similarly. The alcohol evaporates in the first two minutes anyway.

How to store hemp croutons?

In an airtight container at room temperature for up to two days. Do not put them in the fridge, as moisture will take away their crispness. If they soften, place them in an oven preheated to 180°C for three minutes to regain their structure without re-coating.

The store at Bucha does not carry hemp flour and bread. In the food category, you will find hemp teas and sweets for dessert after this soup.

This article is for informational and educational purposes and does not replace consultation with a doctor. If you are pregnant, breastfeeding, taking medications, or have chronic conditions, consult the use of supplements or herbs with a specialist.

Author: Michał Waluk · Published: 2026-06-02 · Updated: 2026-08-15