This molecular gastronomy recipe is based on the reverse spherification technique which is great for ingredients rich in calcium like yogurt. Spherification is the process of shaping liquid in spheres by a thin gelatinous membrane. The main “reaction” is the forming of the gelatinous membrane by combining alginate and calcium.
Makes 10–15
INGREDIENTS:
1000 mL (4 cups) water
5 g sodium alginate powder
100 g yogurt† (do not use no fat or low fat yogurt because the calcium content is lower. Alternatively you can use no fat but you will have to add calcium gluconate)
Sugar
† YOU CAN ALSO USE CERTAIN TYPES OF PURÉE WHICH CONTAIN RELATIVELY HIGH CONCENTRATIONS OF CALCIUM, GREEN LEAVES SUCH AS BASIL, JEW’S MARROW, KALE OR WATERCRESS‡, OLIVE, PEAR, STRAWBERRY, LEMON, MOZZARELLA, TOFU WITH CALCIUM, AND SO FORTH.
‡ TO PREPARE 100 G GREEN LEAF PURÉE, USE 120 G FRESH GREEN LEAVES. BOIL LEAVES IN SALTED WATER (100ºC) FOR 5 MIN, THEN COOL IN COLD WATER, AND MASH IN A FOOD PROCESSOR OR BLENDER.
PROCEDURE:
1) Pour water in a bowl. Add sodium alginate and mix with a hand mixer or a blender.
2) To remove bubbles or lumps in the sodium-alginate solution, place it in the refrigerator until they disappear, usually overnight.
3) Scoop yogurt, place scoops in the sodium-alginate solution.
4) Once the jelly has set (about 2 minutes.), remove the yogurt spheres from the solution (3).
pH of sodium-alginate solution = 7.82
pH of yoghurt = 4.06
NOTE: Sodium alginate will only gel in a pH range of 4- 10. Many store bought juices and foods have a pH below this level because citric or ascorbic acid has been added to extend shelf life. If your spheres fail to form properly using a commercial product, this may be the problem. You can raise the pH of the product using sodium citrate or better yet puree/juice your own fruits and vegetables to spherify. You can test the pH of your liquid using a pH meter.
If you leave the spheres in contact with air, the gel will start to dry and eventually break. You need to store them in a liquid bath. However, since the gel membrane around the sphere is permeable to small molecules, osmosis will occur if submerged in water and dilute the flavored liquid inside the sphere. To preserve the flavor, store them in a bath of the same flavored liquid in the fridge.
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Spherification Quick Tips
1) It is very essential to make sure your calcium is properly diluted. If your solution is too thick to allow a good dilution, you will have to dilute the calcium in a bit of water (or milk) before incorporating it in to your solution.
2) The longer the sphere stays in the bath, the thicker the gel will be. Make sure the spheres do not touch each other in the bath as if they touch they will stick together.
3) You always start with one sphere first to adjust the pouring process and the time in the sodium alginate bath. If the sphere membrane is too subtle and the sphere easily breaks when handling it with the slotted spoon carefully or when plating it, extend the time in the calcium bath until you get the desired strength. Keep in mind that the thinner the membrane the better experience people are going to have when eating it.
4) When you take the sphere out of the alginate bath, it is very important to rinse it well if you want the surface to smooth. Contrary to basic spherification, the gellification in reverse spherification stops after you rinse the spheres.
5) The spheres can be preserved in their original liquid (for example you can keep apple juice ravioles in apple juice) and can be easily served warm if you heat them a few seconds in warm water before serving.
Watch Related Video: How to Make Yogurt Spheres
Watch this short video like watching your favorite cooking show on telly: Molecular Gastronomy: Reverse Spherification to Make Spheres with Liquid Inside
The video shows you the possibilities of reverse spherification, how it works and how to make spheres of different flavors with this technique.
Serving Suggestions
a) Serve with cucumber slices
b) Sprinkle with lemon zest
c) Serve with a raspberry coulis
What is Sodium Alginate?
The chemical compound sodium alginate is the sodium salt of alginic acid. Its empirical formula is NaC6H7O6. Sodium alginate is a gum, extracted from the cell walls of brown algae.
Sodium alginate it is capable of absorbing 200-300 times its own weight in water. As a flavorless gum, it is used by the foods industry to increase viscosity and as an emulsifier. Is a stabilizer for ice cream, yogurt, cream, and cheese. It is a thickener and emulsifier for salad, pudding, jam, tomato juice, and canned products. In the presence of calcium and acid mediums, it forms resilient gels. It is a cold gelling agent that needs no heat to gel. It is most commonly used with calcium chloride in the spherification process to react quickly to form a gel membrane.
What is Calcium Chloride?
Calcium chloride, CaCl2, is a salt of calcium and chlorine. It is listed as a permitted food additive in the European Union for use as a sequestrant and firming agent with the E number E509. It is considered as generally recognized as safe (GRAS) by the U.S. Food and Drug Administration.
Food grade pellets calcium chloride is used in post-harvest treatments of fruits and vegetables. Calcium chloride is also used in food and beverage processing, high fructose corn syrup production, and dairy foods processing.
As a firming agent, calcium chloride is used in canned vegetables, in firming soybean curds into tofu and in producing a caviar substitute from vegetable or fruit juices. It is commonly used as an electrolyte in sports drinks and other beverages, including bottled water. The extremely salty taste of calcium chloride is used to flavor pickles while not increasing the food's sodium content. Calcium chloride's freezing-point depression properties are used to slow the freezing of the caramel in caramel-filled chocolate bars.
What is Spherification?
Spherification is the culinary process of shaping a liquid into spheres which visually and texturally resemble caviar. The method that enables you to imbue a flavorful liquid with the appearance of being solid, an illusion that's broken when the spheres burst with flavor as they're eaten. The technique was originally discovered by Unilever in the 1950s and brought to the modernist cuisine by the creative team at elBulli under the direction of executive chef Ferran Adrià.
Watch a Video: Introduction to Spherification
There are two main methods for creating such spheres, which differ based on the calcium content of the liquid product to be spherified.
A) Direct spherification, for flavored liquids (such as fruit juices) containing no calcium, the liquid is thoroughly mixed with a small quantity of powdered sodium alginate, then dripped into a bowl filled with a cold solution of calcium chloride, or other soluble calcium salt.
B) Reverse spherification, for use with substances which contain calcium or have high acid/alcohol content, requires dripping the substance (containing calcium lactate or calcium lactate gluconate) into an alginate bath. A more recent technique is frozen reverse spherification, which involves pre-freezing spheres containing calcium lactate gluconate and then submerging them in a sodium alginate bath. All three methods give the same result: a sphere of liquid held by a thin gel membrane, texturally similar to caviar.
Watch: How to Perform Frozen Reverse Spherification
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Reverse spherification involves infusing a liquid with a mixture of calcium lactate gluconate and calcium lactate and then submerging it in a bath of sodium alginate. It is referred to as ‘REVERSE’ because the process is the mirror image of the BASIC spherification where the liquid is infused with sodium alginate and submerged in a bath of calcium lactate.
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Pros and Cons of Reverse Spherification
PROS:
1) Liquids with a high level of acidity are no problem for reverse spherification and will need no adjustment as in the basic method.
2) Reverse spherification is more versatile than basic spherification as it can make spheres with almost any product. It is best for liquids with high calcium content or alcohol content which makes them great for cocktails and dairy products like cheese, milk, cream and yoghurt.
3) Reverse spherification produces a thicker membrane than basic spherification making it more durable and manageable. While it will not be indestructible, you won’t need to take the same care as with the basic technique.
4) The resulting sphere is long-lasting and can be stored for later consumption. In contrast with basic spherification, the gelification process stops as soon as you remove the spheres from the sodium alginate bath and rinsed with water. This is because there is no more sodium alginate to react with the free calcium ions inside the sphere and all the sodium alginate molecules are already bound in the gel.
CONS:
1) The sodium alginate bath needs to rest for 12-24 hours before using it for reverse spherification to eliminate the air bubbles created by the process of dissolving the sodium alginate with the immersion blender.
2) Getting a perfect sphere takes a bit of practice with reverse spherification. The liquid will quickly take shape once poured into the sodium alginate bath. If it is poured slowly you’ll end up with a curving amoeba like shape. Additionally the spheres need to be kept separated from each other in the bath or they will stick together.
3) It is a little harder to get a perfect sphere on the plate with reverse spherification than with basic spherification. You are pouring the main ingredient into a viscous bath, the spheres tend to stick to each other if you don’t separate them in the bath and the thicker membrane maintains the shape better which is great if you were able to create a perfect sphere but not if your spheres are distorted. Frozen reverse spherification solves this problem if the main ingredient can be frozen.
4) Due to the thicker membrane, a gelatinous substance will be left in the mouth once the sphere has been popped. It is quite small and easily swallowed, but still detracts somewhat from the clean experience of basic spherification
5) The flavored liquid may need to be thickened with xanthan gum and if air bubbles get trapped in the process, you may need to wait a few hours to eliminate them.
6) Reverse spherification takes much longer than basic spherification as the sodium alginate bath needs 24 hours of rest time to eliminate air bubbles unless you have a chamber vacuum sealer.
7) Reverse spherification is not great for making caviar as the main ingredient needs to be thickened to be able to penetrate the dense sodium alginate bath and cohere into a sphere.
Where to Get a Reverse Spherification Kit?
You can easily purchase an affordable Reverse Spherification Kit online. This Reverse Spherification Kit contains everything that you need to get started making modernist ravioli or large yogurt spheres. It is the simplest spherification technique, perfect for beginners. The kit includes ingredients and tools necessary for reverse spherification and frozen reverse spherification as well as troubleshooting tips.
References:
Myhrvold, Nathan and Maxime Bilet. 2012. Modernist Cuisine at Home. The Cooking Lab; Pck Slp Sp edition. ISBN-10: 0982761015
Potter, Jeff. 2010. Cooking for Geeks: Real Science, Great Hacks, and Good Food. O'Reilly Media, Inc. ISBN 0-596-80588-8.
Sanchez , Jose. 2014. Molecular Gastronomy: Scientific Cuisine Demystified. Wiley; 1 edition. ISBN-10: 111807386X
Watch a Short Video... Molecular Gastronomy Video- Molecular Cooking is Cooking: Molecular Gastronomy is a Scientific Activity
ANOTHER video demonstration: Demonstration of Reverse Spherification
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