Return of the Rainbow Flag

Last Valentine's Day I made a post which featured a rainbow flag made from synthetic caviar. Now is probably a good time to post an explanation of how it was done.

Synthetic Caviar

Technical Background

Synthetic caviar is produced by a process known as Spherification. This technique relies on an unusual property of the substance sodium alginate.

Before I go any further, sodium alginate is not a weird and sinister chemical synthesised in the laboratory of some evil food corporation, but a substance extracted from seaweed. You could think of it as a vegetarian version of gelatin. You will have eaten it many times before; amongst other things, it's used to create the "cherries" in fruit buns and the fillings in stuffed olives.

Sodium alginate has the same effect as gelatin (i.e. converts a liquid into a gel), but it achieves this by a different mechanism, and this mechanism can be exploited to create unusual food items.

When a small quantity of sodium alginate is dissolved* in water, it gives the resulting solution a syrupy texture. This solution is stable, and unlike gelatin, doesn't set when it becomes cold (although it will become noticeably more viscous). Sodium alginate is often used as a thickening agent in foods for this reason.

[* = technically, it doesn't actually dissolve but in fact disperses; the difference is academic from the point of view of cooking.]

Where the interesting part comes in is that when sodium alginate comes into contact with a liquid containing calcium, it converts to calcium alginate, which forms a firm gel. Once formed, this gel is stable, moderately tough and unaffected by temperature.

So what you can do is add sodium alginate to an appropriate liquid, drip blobs of it into a bath containing calcium solution, and then fish them out once the outside has firmed up. You end up with a sphere that's firm on the outside, but with a liquid centre.

You can also do Reverse Spherification where you drip a calcium-rich substance into a sodium alginate bath.

With the right ingredients, you can make not only synthetic caviar, but also a wide variety of other unusual foods.

Plusses

• Looks really cool.
• Not difficult to do. The process can be performed by a school child.
• It is unusual enough that it can be a science fair project, or can be an impressive party trick. The spheres are unaffected by alcohol, so you can make all sorts of weird cocktails with them. Try dressing up as a mad scientist and serve them up in test tubes, beakers, etc.
• Ingredients aren't overly expensive.You only need tiny quantities anyway.
• The main ingredient is extracted from seaweed and is environmentally sustainable, acceptable to vegans, Halal and Kosher. So (assuming you choose your other ingredients wisely) you're safe from offending pretty much anyone.

Minuses

• Can be time-consuming to make more than a relatively small quantity (you can buy special tools to make them in bulk, but these are fairly expensive).
• Must be used soon after preparation. The texture starts to deteriorate after a few hours (depending on the ingredients, the spheres either start weeping or harden up right through). You can make up the alginate solution the night before, but not the spheres.
• Ingredients aren't readily available at your local grocery store (although can be ordered on line fairly easily). 

The Rainbow Flag of caviar [click for larger image]

The Recipe

If you think you might want to give it a go, a good starting point would be to download the Texture - A hydrocolloid recipe collection, by Martin Lersh from the Khymnos blog.

Don't be intimidated by the size and technical detail. Go to the "Sodium alginate" section and look over some of the recipes for caviar.

For a pictorial description of the process (with some incredible photography) check out the Luxirare blog. Don't let the professionalism of this site put you off, either; you can achieve amazing effects without any special technical skills or equipment. It's really easy, in fact.

The synthetic caviar featured on this blog was made as follows:

1) Firstly, a 1% solution of sodium alginate was made (1 g of sodium alginate in 100 ml of hot water).

This is actually the most difficult part of the whole process. Sodium alginate doesn't dissolve in the sense that sugar or salt does, but it basically absorbs water and swells up into a lumpy mass of jelly, with hard bits in it. Left by itself this mass will keep absorbing water and most likely will eventually attain an even consistency, however this would take a very long time and you need to give it some help.

Some people use a blender to dissolve the sodium alginate. This is easy to do and works very quickly, but beats an enormous amount of air into the mixture, which means it has to be left for several hours for the air bubbles to clear.

I used very hot water (just off boiling), and slowly added it to the alginate, mixing by hand all of the time. A flat tool like an ice-cream stick or the blade of a butter knife works best for mixing for mixing; with a fork, lumps get stuck between the tines.

After about 10 minutes of mixing, the mass was nearly all broken up with a few harder lumps floating around. When left to sit for half an hour, the lumps had dissolved and all of the air bubbles had cleared. I'm not sure whether the hand mixing put in fewer air bubbles, or whether the hot water made them clear faster.

BTW, This solution is stable and can be kept in the fridge for at least a few days.

2) The solution was then portioned out into a number of small glasses, one for each colour and appropriate colourings and flavourings (rose water, grape juice etc.) were added. The original alginate solution was made more concentrated than was required in order to allow 50% or so extra liquid in the form of flavourings to be added.

You will have to experiment with what works best for you here. I found that simple food colours and essences were easiest to deal with, and they would be recommended as a starting point. I found that very acidic (lemon juice) or sticky (mango nectar) liquids were hard to deal with. I tried to use sodium citrate to reduce the acidity of the lemon juice, but it didn't help much and simply added a salty flavour.

3) 2 g of calcium chloride was then dissolved in 200 ml of warm water in a glass.

Calcium chloride can impart a (very slightly) salty taste. This is not generally noticeable, but may be an issue when using very subtle flavourings. In this case, you can substitute calcium lactate.

4) The spheres were created by dripping the appropriate solution into the calcium chloride solution with a 10 ml syringe. Approx 5 ml of solution was used at a time, after which the spheres were retrieved from the solution with a sieve, rinsed in water and set aside. The spheres only need to sit a short time in the solution (say 30 seconds) to firm up.

The Ingredients

The Main Ingredients

In Australia, you can get the ingredients from Gourmet Goldmine and The Red Spoon ^co.

It's best to get the smallest size packs, which are around 80 g. An evening's experimenting might only require around 2 g, so even 80 g will go a long way.

You'll also need scales capable of measuring down to about 0.1 g and a 10 ml syringe. You can get the syringe on line or from a chemist. Don't be scared; it is not illegal to buy syringes in Australia.