Chocolate part 1:3 - why it seizes with just a little water, ...and what to do about it

If just a little amount of water finds its way into melting chocolate, it goes all grainy and solid - it seizes/curdles. There is really no fix to the problem. However, if some more water is added, the chocolate suddenly becomes fluid again. How come?

In three recent posts in the Swedish food blog Matmolekyler ("Food molecules"), Malin discusses the physics of chocolate. In the third one, the question arose on what really happens when a little water makes the chocolate go all grainy, and why adding some more water solves the problem. It made me start looking around in my "standard" food literature base: O'Corriher, McGee, Belitz/Grosch/Shieberle, Barham, Pedersen, Dahlgren. Although O'Corriher came closest, none of them had the answer to Malin's question: "is there an oil-in-water emulsion going on or something?". Finally, Beckett did have the answer, maybe not very surprising, since the name of the book is "The Science of Chocolate". However, it took some serious searching even in this book in addition to a few research papers. Hence, I expect to write a couple of more posts on chocolate since I've dug into the topic.

Chocolate seems like no easy medium to work with, and according to books on the topic I have to follow loads of specific directions in order to avoid failing. I've postponed it in fear of failing. The solution to the problem: start by failing on purpose!

The problem
It all starts when trying to melt the chocolate. (Cook)books say:

1. the chocolate should be carved or cut into small pieces
   
2. use low heat, preferably a water bath or double boiler , stirring continuously
   
3. don't ever get water in the chocolate (either from the water bath or from moist equipment)
   
4. (microwave oven might be used as an alternative, although carefully)
   

I have an inherent need of doing things as easy as possible, and using the double boiler method makes me go nuts waiting for the last bits to melt. To me, water bath equals splashing warm tap water around in the kitchen sink. In that respect, points 2-3 pose a problem, because getting water in the chocolate results in this:

Left: 100 g melted pure (55%) chocolate
Right: the same melted chocolate after adding less than a teaspoon of water

In fact, so little water is needed for this to happen that steam from a boiling pan might be enough to make the chocolate go grainy. When this happens, there is no way back to the pure chocolate. However, it is perfectly usable for other purposes such as chocolate sauce, ganache, drinking cocoa etc. Alternatives to using water bath or a double boiler principle. In stead of water bath or double boiler, I usually use the microwave or even melt the chocolate directly in the pot using low heat and stirring continuously (have to be very careful). However, I love sabotage experiments. When recipes tell me by all means not to do something, the little boy awakens and I go for it. And that's the point in this post: what happens when chocolate seizes?

To understand what happens one need to know what chocolate is...

Basically, chocolate is

• cocoa fat (cocoa butter) - water repelling
  
• sugar particles - water loving
  
• cocoa particles - water repelling
  
• lecithin emulsifier - water repelling and water loving
  
• (for milk chocolate: milk fat and/or milk powder)
  

Chocolate is a dispersion, consisting of solids distributed in a fatty (continuous) phase. The miniscule cocoa particles (mean diameter ca. 0.016 mm) are hydrophobic and prefer staying close to the fat. The sugar particles, too small for our tongue to notice them as grainy when properly distributed, are however hydrophilic (water loving), and repelled by the fat. An important function of the lecithin emulsifier is to build protecting layers around the sugar particles so that they don't separate from the fatty phase and give a grainy texture. The emulsifier is commonly lecithin (lecithin is also a natural constituent of egg yolk, and the main reason for why the yolk doesn't split into a fatty and a watery phase).

Schematic drawing of the above photos
Left: pure chocolate. Right: chocolate after adding just a little water

What happens when water gets into the chocolate?
In it's solid form, pure chocolate is a relatively stable system virtually free of water (0.5-1.5% by weight). When the chocolate is melted, the stable dispersion is challenged. If just a small amount of water (or steam) finds its way into the chocolate, the water molecules form droplets, since they don't want to mingle with the fat. Since water and sugar like to mingle, the sugar particles are wetted by the water. The result is "the sugar bowl effect", just as when a few drops of water are spilled into a sugar bowl. The tiny sugar particles in the chocolate become moist and cling together giving larger lumps (agglomerates). The result is an inhomogeneous mixture between these sugar agglomerates and the cocoa-fat-cocoa-particle mixture. These won't mix evenly because the sugar has gone watery (the lecithin is probably not capable of stabilising such large amounts of hydrophilic constituents). Since sugar is a major ingredient in chocolate, it all goes grainy. A water content of 3-4% by weight is enough to make the chocolate seize. Since the chocolate might contain som water already the critical amount of added water might be as low as 1.5% by weight (1/3 teaspoon on 100 g, ref. Afoakwa et al.).

Add some more water, and everything is "fine" again
If the chocolate has seized, there is really no way back to the original chocolate. However, if some more water is added, the grainy mass magically turns silky smooth again. What happens is that the emulsion inverts; whereas fat was the continuous phase in chocolate, now water is the continuous phase and the fat is distributed/"dissolved" in the water:

Left: 100 g melted pure (55%) chocolate, seized with less than a teaspoon water

Right: the same chocolate after a tablespoon of water

A definite explanation of this was in fact rather difficult to find, and the only literature source stating this explicitly was in fact Beckett's book (The Science of Chocolate. Afoakwe also states this, but refers to Beckett's book). He writes that about 20% by weight water vs. chocolate is needed to achieve such a phase inversion, whereas . O'Corriher writes that you need a minimum of 1 tablespoon water per 56 g (2 oz) chocolate. This roughly equals 30% by weight. Note that this is total amount of water; if cream, butter or some other water-containing ingredient is used, this contribution counts.

Schematic drawing of the above photos
Left: seized chocolate. Right: after adding a tablespoon of water

Since chocolate contain plenty of emulsifiers, this emulsion might be quite stable and a good starting point to many wondrous things such as drinking cocoa, chocolate sauce, ganache/truffles, foam/mousse ("chocolate chantilly") or even a chocolate mayonnaise.

What might be taught/learned

• dispersions: emulsions and solid dispersions
  
• solutions/solubility, hydrophilic and hydrophobic properties
  
• experimental and cooking skills (dealing with chocolate)
  
• observational skills (what to look for in an experiment)
  

Reference, scientific paper
Afoakwa, Paterson & Fowler: "Factors influencing rheological and textural qualities in chocolate - a review". Trends Food Sci. Tech., 2007, 290-298.

References, books with relevant information on the subject
Beckett: The Science of Chocolate (1. ed.). Cambridge : Royal Society of Chemistry 2000.
Belitz, Grosch & Schieberle: Food Chemistry (3. ed.). Berlin: Springer 2004.
Dahlgren, Ö.: Laga mat - hur man gör och varför. Stockholm : Liber utbildning, 1994.
McGee, H.: McGee on Food and Cooking. London: Hodder and Stoughton 2004.
O’Corriher, S.: Cookwise. New York: William Morrow 1997.
Pedersen, T.: Kemien bag gastronomien. Copenhagen: Nyt Nordisk Forlag 2005.