Modern Industrial Chemicals (part 3) - Making gels: Carrageenan & Agar - Chocolate Panna Cotta

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3.2. Making gels: Carrageenan

Carrageenan has been used in food as far back as the 15th century for thickening dairy products. Commercial mass production of carrageenan gums became feasible after World War II, and now it shows up in everything from cream cheese to dog food, where it acts as a thickener. Modernist cuisine dishes use it for the same reason, although typically to thicken liquids into gels in ways that we might not think of at first glance (beer gel, anyone?).

Instructions for use. Mix 0.5% to 1.5% carrageenan into room-temperature liquid. Gently stir liquid to avoid trapping air bubbles into the gel; lumps are okay at this stage. (They’re hard to get out unless you have a vacuum system.) Allow to rest for an hour or so; carrageenan takes a while to rehydrate. To set carrageenan, bring to a simmer either on a stovetop or in an oven. If you are working with a liquid that can’t be heated, create a thicker concentration using just water, heat that, and then mix it into your dish.

Uses. Carrageenan is used to thicken foods and to control crystal growth (e.g., in ice cream, keeping ice crystals small prevents a gritty texture). Carrageenan is commonly used in dairy (check the ingredients on your container of heavy whipping cream!) and water-based products, such as fast-food shakes (keeps ingredients in suspension and enhances mouth-feel) and ice creams (prevents aggregation of ice crystals and syneresis, the expulsion of liquid from a gel).

Origin and chemistry. Derived from seaweed (such as Chondrus crispus—common name Irish moss), carrageenan refers to a family of molecules that all share a common shape (a linear polymer that alternates between two types of sugars). The seaweed is sundried, treated with lye, washed, and refined into a powder. Variations in the molecular structure of carrageenan cause different levels of gelification, so different effects can be achieved by using different types of carrageenan (which, helpfully, grow in different varieties of red seaweed). Kappa carrageenan (k-carrageenan) forms a stronger brittle gel, and iota carrageenan (i-carrageenan) forms a softer brittle gel.

On the molecular level, carrageenan, when heated, untangles and loses its helical structure (left); when cooled, it reforms helices that wrap around each other and form small clusters (right). The small clusters can then form a giant three-dimensional net that traps other molecules.

Technical notes
  i-carrageenan k-carrageenan
Gelling temperature 95–149°F / 35–65°C 95–149°F / 35–65°C
Melting temperature 131–185°F / 55–85°C 131–185°F / 55–85°C
Gel type Soft gel: gels in the presence of calcium ions Firm gel: gels in the presence of potassium ions
Syneresis No Yes
Working concentrations 0.3% to 2% 0.3% to 2%
Notes Poor solubility in sugary solutions Interacts well with starches Insoluble in salty solutions Interacts well with nongelling polysaccharides (e.g., gums like locust bean gum)
Thermoreversible Yes Yes

Gelled Milk with Iota and Kappa Carrageenan

This isn’t, in and of itself, a tasty recipe (add some chocolate, though, and you’ve got something close to commercial prepackaged food). Still, it will give you a good sense of what adding a gelling agent does to a liquid and provides a good comparison between soft and brittle gels.

Flexible brittle version

In a saucepan, whisk to combine and then bring to a boil:

1 teaspoon (1.5g) iota carrageenan

3.5 oz (100 ml) milk

Pour into a glass, ice cube tray, or mold and chill in the fridge until set (about 10 minutes).

Firm brittle version

Again in a saucepan, whisk to combine and then bring to a boil:

1 teaspoon (1.5g) kappa carrageenan

3.5 oz (100 ml) milk

Pour into a second glass, ice cube tray, or mold and chill in the fridge until set.


  • Try modifying the recipe by adding 1 teaspoon (4g) of sugar, substituting some cream for a portion of the milk, popping the mixture into a microwave for a minute to set it, and pouring it into a ramekin that has a thin layer of jam or jelly and toasted sliced almonds on the bottom. Once gelled, invert the set gel onto a plate for something roughly approximating a flan-style custard.

  • Since the carrageenan is thermoreversible (once gelled, it can still be melted), you can take a block of food gelled with kappa carrageenan, slice it into cubes, and do silly things like serve it with coffee or tea (one lump or two?).

  • You can take a firm brittle gel and break up the structure using a whisk to create things like thick chocolate pudding.

3.3. Making gels: Agar

Agar—sometimes called agar-agar—is perhaps the oldest of all the food additives commonly used in industry, but has only recently become known in western cuisines, mostly as a vegetarian substitute for gelatin. First used by the Japanese in the firm, jelly-type desserts that they’re known for, such as mizuyokan, agar has a history stretching back many centuries.

When it comes to playing with food additives, agar is one of the simplest to work with. You can add it to just about any liquid to create a firm gel—a 2% concentration in, say, a cup of Earl Grey tea will make it firmer than Jell-O—and it sets quickly at room temperature. It comes in two general varieties: flakes or powder. The powdered form is easier to work with (just add to liquid and heat). When working with the flake variety, presoak it for at least five minutes and make sure to cook long enough so that it breaks down fully.

Instructions for use. Dissolve 0.5% to 2% agar by weight in cold liquid and whisk to combine. Bring liquid to a boil. As with carrageenan, you can create a thicker concentrate and add that to a target liquid if the target liquid can’t be boiled. Compared to carrageenan, agar has a broader range of substances in which it will work, but it requires a higher temperature to set.

Use. Agar is a gelling agent, used in industry in lieu of gelatin in products such as jellies, candies, cheeses, and glazes. Since agar is vegetarian, it’s a good substitute in dishes that traditionally call for gelatin, which is derived from animal skins and bones. Agar has a slight taste, though, so it works best with strongly flavored dishes.

Origin and chemistry. Derived from seaweed. Like carrageenan, agar is a seaweed-derived polysaccharide used to thicken foods and create gels. When heated above 185°F / 85°C, the galactose in agar melts, and upon cooling below 90–104°F / 32–40°C it forms a double-helix structure. (The exact gelling temperature depends on the concentration of agar.)

During gelling, the endpoints of the double helices are able to bond to each other. Agar has a large hysteresis; that is, the temperature at which it converts back to a gel is much lower than the temperature at which that gel melts back to a liquid, which means that you can warm the set gel up to a moderately warm temperature and have it remain solid. 

Agar at the molecular level. When heated, the molecule relaxes into a relatively straight molecule (upper left) that upon cooling forms a double helix with another agar molecule (center). The ends of these double helices can bond with other agar double helices (upper right), forming a 3D mesh (left).

Technical notes
Gelling temperature 90–104°F / 32–40°C
Melting temperature 185°F / 85°C
Hysteresis 140°F / 60°C
Gel Type Brittle
Syneresis Yes
Concentrations 0.5%–2%
Synergisms Works well with sucrose
Notes Tannic acid inhibits gel formation (tannic acid is what causes overbrewed tea to taste bad; berries also contain tannins)
Thermoreversible Yes

Chocolate Panna Cotta

Agar can be used to provide firmness, as this example shows. In a saucepan, whisk together and gently simmer (below boiling—just until small bubbles form on surface) for one minute:

3½ oz (100g) milk

3½ oz (100g) heavy cream

½ pod vanilla bean, sliced lengthwise and scraped

8 teaspoons (20g) powdered sugar

1 teaspoon (2g) agar powder

Turn off heat, remove vanilla bean pod, and add, briefly stir, and let rest:

3.5 oz (100g) bittersweet chocolate, chopped into fine pieces to assist in rapid melting

After a minute, add and whisk to thoroughly combine:

2 eggs yolks (reserve whites for some other recipe)

Pour mixture into glasses, bowl, or molds and store in fridge. The gel will set in as little as 15 minutes, depending upon the size of the mold and how long it takes the mousse to drop below agar’s setting point (around 90°F / 32°C).


  • The agar provides a firmness that creates a stronger mousse than that created when using gelatin, so you should plan to use this mousse in applications where firmness is a desired trait.

  • This chocolate mousse, while good by itself, really works better as a component in a dish. Example uses: roll a ball of the mousse in toasted nuts to create a truffle-like confection, spread a layer of the mousse into a prebaked pie crust and top with raspberries and whipped cream, or smear a thin layer of the mousse in the bottom of a bowl and place a small scoop of vanilla ice cream and some fresh fruit on top.

  • When working with a vanilla bean, use a spoon or the edge of a knife to scrape the seeds from the pod, and add both pod and seeds to your mixture. Scraping the bean helps get the vanilla into the mixture more quickly.

Rum Screwdriver Gel

In a small mixing bowl, measure out:

8 teaspoons (40g) rum

In a saucepan, whisk to combine, and bring to a boil and hold for an additional minute:

10 teaspoons (50g) orange juice

¼ cup (40g) sugar

1 teaspoon (2g) agar powder

Pour the hot liquid into the small mixing bowl, and stir thoroughly to combine. Transfer mixture to a glass, ice cube tray, or other food mold and store in fridge for 30 minutes or until set.


  • Yes, these are basically rapid-setting Jell-O shots. Using agar allows for a higher percentage of alcohol—you can gel rum by itself if careful—but make sure to leave enough juice in for flavor.

  • Play with substitutions. You can replace the rum and orange juice with fluids such as Malibu and coconut milk.

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