Culinary Deep Dive: Frozen Reverse Spherification

Beef Shortrib Tartare with Curry Sphere. Photo by Chris Montgomery.

"Spherification" is a method of containing a flavorful liquid substance - juice, soup, sauce - inside a clear, flavorless membrane, allowing it to retain the shape of a plump, round sphere. When eaten, the membrane is easily punctured by the diner's teeth and the internal liquid is released in a blaze of glory! This is a fantastic method of presentation for any type of liquid - you can see it being used above as a curry sauce for beef tartare dish I made for my tasting restaurant I Forgot It's Wednesday. Instead of mixing the sauce with the beef tartare, I allowed the guests to pop the sphere themselves and do a little DIY action with their tartare. Most famously, Ferran Adria showcased this method with his "Liquid Olive" at elBulli - a dish still being continued by his brother Albert at Barcelona's Tickets restaurant.

There is basic spherification and there is reverse spherification. As the names imply, the two are inverse processes of each other: basic spherification submerges a liquid with sodium alginate in a bath of calcium; reverse spherification submerges a liquid with calcium in a bath of sodium alginate. In short, reverse spherification is the versatile method because it:

1. Allows for more perfect spheres if you use the "frozen" method (we'll get into that).

2. Can work with liquid that contain calcium (i.e. any type of dairy product) or alcohol.

3. Can be stored for later use.

4. Keeps the liquid the same viscosity before/after the process.

5. Relatively strong, stable membranes allow for the spheres to be served both cold, warm, or hot and is less susceptible to breaking.

Within reverse spherification, there is a fantastic "hack" called Frozen Reverse Spherification, which is what I'll be getting into for this article. This is my preferred method of making spheres as it's very hands-off, easy to explain, forms perfect spheres, and works with almost any liquid. The only downside is that you can't use alcohol-based liquids for this method as they will not freeze. It involves taking the liquid, mixing it with calcium lactate gluconate powder, freezing it into a half-circle mold, and plopping them into a bath of hot sodium alginate. You then store them in the original liquid until you want to serve (I find they hold ~1 week or so). Here's a detailed step-by-step with equipment and instructions:

1. Make a delicious, tasty liquid you want to serve. The viscosity of said liquid should be somewhat runny. I've done purees as spheres and they are still tasty, but the "popping" sensation is muted, so I would recommend something that is the same thinness as pancake batter.

2. Add calcium lactate gluconate at 2% of the liquid's total weight. IE: Your liquid weights 1000 grams, add 20g of calcium lactate gluconate. The liquid also must be very, very flavorful because the addition of calcium lactate gluconate alters the flavors a little bit, and the powder is also known to numb the taste buds a touch, so you want to make sure that your liquid is powerful enough to override those two issues. I recommend calcium lactate gluconate vs. calcium lactate as it is less perceptible in flavor.

To do this, you need:

3. Once you have your liquid mixed with calcium lactate gluconate, you need to transfer the liquid into a silicon half-circle mold and freeze them until solid. This usually takes 3-4 hours. I recommend placing the mold on a quarter-sheet tray so you have a solid surface to work with. If you need exact measurements of your spheres, you can place the entire quarter sheet tray on your 0.1 gram scale and measure in the same amount per semi-circle mold. PRO TIP: you don't need the "special" half-circle mold Molecular Recipes sells online, you can use the one below.

To do this you need: the below + a spoon and plastic wrap

4. Make a sodium alginate bath. You'll be adding sodium alginate at 0.5% of the total water weight. IE: If you have 1000 grams of water, you add 5g of sodium alginate. It's important to use distilled (or at least filtered) water to do this so there's not impurities in the water. I recommend making a bath with at least 850g of water (approximately 1 quart container) per round of spherification. You'll again be adding the sodium alginate while you are blending the water with an immersion blender or else it'll clump. You'll see some of the sodium alginate stick to your immersion blender and that's ok, just try to incorporate as much as possible. This solution will be very bubbly and somewhat opaque when you first mix it, it needs to sit 12-24 hours in order for the bubbles to dissipate so make this ahead of time!

To do this, you need:

5. Once your liquid is solidly frozen in little molds, you are ready for sphere-making! First, set up your station with 2 large, deep bowls, 1 pint container filled with distilled (or filtered) water, and multiple half-pint containers filled with the original liquid or a neutral flavored oil - in that order. It is important the 2 bowls are deep as the spheres need some space to move around. The water is to rinse off the sodium alginate solution from the finished spheres. The half-pints are the best way to store the spheres (usually 8 spheres max per half-pint) as you don't want spheres sitting on top of each other. You can store the spheres either in the original liquid or some oil - water is not recommended as the membrane of the spheres are is porous and the spheres will start leaking over time.

To do this, you need:

6. Alrighty! Now, since your spheres are frozen the sodium alginate bath must be heated to around 65C in order to melt the spheres down. It's important for the spheres to melt again or else it's difficult to determine if the membranes have formed properly. I usually just do this in the microwave. Once heated, split the sodium alginate bath evenly into the first 2 bowls.

To do this, you need:

7. Remove the frozen spheres from the mold and plop the into the 1st bowl. I recommend only doing a few at a time (I usually do 3-4 max) but it depends on the size of your bowl. You want the spheres to have plenty of space to move around without touching each other. It is important the spheres do not touch or else the membranes will gel together and you'll have conjoined twin spheres that burst when you pry them apart. Sphere membranes take ~3 minutes to form in the sodium alginate solution, so I use 2 bowls of sodium alginate so there's not a big bottleneck at the beginning. After 1 minute in the 1st bowl, I'll transfer the spheres to the 2nd bowl to continue "cooking". This way spheres in the molds do not melt while you're going through this process. You'll be using a small slotted spoon to move the spheres from bowl to bowl. After the 2nd bowl, you can scoop up each sphere to ensure the membrane is formed thoroughly (the sphere will be perfectly round and sit on the spoon without any leaks), rinse it in the water, and place it in the half-pint for storage.

To do this, you need:

8. Repeat until you're finished with all your spheres. You'll usually have a couple break or leak on you, so always make a few extra! Once complete, label your half-pints clearly and keep them in the refrigerator in a place where they won't be disturbed. Enjoy!

TIPS:

1. I find the spheres last ~1 week or so, so you can definitely make them in advance.

2. If you want to prep spheres more in advance than 1 week, I recommend making the sodium alginate solution (that lasts forever) and keep the spheres frozen in the molds until needed.

3. To serve the spheres at room temperature, simply bring out the half-pint containers and leave them to warm up to room temperature.

4. To serve the spheres hot, place the spheres in an oven-safe, shallow container and cover with oil. Let warm at 350F for 2-3 minutes. Make sure to keep an eye on them as the oil will start to bubble eventually and that intense bubbling action will pop all the membranes. I do not recommend doing this while covering the spheres with the original liquid as that will bubble much faster than a neutral, processed oil like canola.

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