15 Mar 2009

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

Revised September 6th 2012 (structure figures and name of Corriher corrected, a note added)

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: Corriher, McGee, Belitz/Grosch/Shieberle, Barham, Pedersen, Dahlgren. Although 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 - somewhat unclear*
  • 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. It contains miniscule cocoa particles (mean diameter ca. 0.016 mm) and sugar particles too small for our tongue to notice them as grainy when properly distributed. The sugar is 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 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 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)


*Note: Some sources (Rowat et al., 2011, and these ppt slides by Naveen Sinha) state that the cocoa particles are hydrophilic (water loving) and that the emulsifier surrounds these rather than (or just as much) as the sugar particles. I have not been able to confirm this and have thus drawn it as neither water loving or water repelling. However, I've found a couple of papers stating that the cocoa particles in fact contain fat (points towards water repelling, see Do et al., 2011) and that the emulsifier primarily attaches itself to the sugar particles (Vernier cited in Svanberg et al., 2011).


References, scientific papers

Afoakwa, Paterson & Fowler: "Factors influencing rheological and textural qualities in chocolate - a review". Trends Food Sci. Tech., 2007, 290-298.
Do, Vieira, Hargreaves, Mitchell & Wolf: "Structural characteristics of cocoa particles and their effect on the viscosity of reduced fat chocolate". LWT - Food Sci. Tech., 2011, 44, 1207-1211.
Rowat, Hollar, Stone & Rosenberg: "The Science of Chocolate: Interactive Activities on Phase Transitions, Emulsification, and Nucleation". J. Chem. Ed.201188, 29-33
Svanberg, Ahrné, Lorén & Windhab: "Effect of sugar, cocoa particles and lecithin on cocoa butter crystallisation in seeded and non-seeded chocolate model systems". J. Food Eng.2011104, 70-80.

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.
Corriher, S.: Cookwise. New York: William Morrow 1997.
Pedersen, T.: Kemien bag gastronomien. Copenhagen: Nyt Nordisk Forlag 2005.

23 comments:

  1. Very nice post. If I get a tiny bit of water into melting chocolate, I add some more solid chocolate to it and stir. I had never understood what was going on. Its is amazing how intricate soft condensed matter can be.

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  2. Good point about repairing. Do you need to stir vigorously? As I interpret this, it is in fact possible to repair if just a small amount of water gets into the chocolate by adding enough chocolate to get the water percentage below 3-4% again. However, I wonder how this can fix the problem of the sugar "lumps" giving a grainy texture. I guess I'll have to try and see...

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  3. Nice pice Erik. Fascinating explanation, and what a fine balance between effects it is :) Regarding the chocolate mayonnaise, it seemed a bit boring solution, using egg as the emulsifier and chocolate as oil. A more interesting test would be to see how much oil can you emulsify with the lecithin available in the chocolate, thus mixing oil and molten chocolate to a mayo.

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  4. Jonas: you're so right. In fact I did think about the possibility of making chocolate mayonnaise using only chocolate, water and oil. I also made a very rough attempt, but was unfortunate enough to splash inn too much oil at one time and the emulsion inverted (from W/O to O/W). It probably needs some fine tuning to be really successful. I suppose one might use Hervé's recipe for chocolate chantilly as starting point and stir in oil instead of whipping in air. Maybe a follow-up post on this?

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  5. Jonas: I did some more rough experiments this afternoon. Using two different chocolate:water ratios, that is 2:1 and 1:2 (the latter being close to the ratio in the chocolate chantilly recipe). It seems like the amounts of emulsifiers aren't enough to support a mayonnaise of sufficient viscosity. Upon addition of rape seed oil the emulsion becomes increasingly viscous, but suddenly inverts (seen from a sudden drop in viscosity) before a proper mayonnaise texture is reached. The major difference compared to ordinary mayonnaise is obviously the large amounts of fat in the chocolate compared to egg yolk. Of course, there might be other reasons, and I now regret that I didn't take any courses in colloid chemistry. If the problem is lack of emulsifier, one might try "fortifying" the chocolate with some more emulsifier of some kind. Any tips are welcome, and I'll provide the workforce and chocolate. However, I don't think I'll do many more experiments throwing away chocolate unless they're promising

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  6. A very nice post Erik. I've actually wondered about this, but never had the required time and courage to start researching this topic ;)

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  7. Wow... Interesting. Reminds me a bit of Heston Blumenthal's video. It's on YouTube under Heston Blumenthal Chocolate Mousse

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  8. Roberto: yes. In fact, I already linked to it in the end of the post ("foam/chantilly").

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  9. Erik - I have been experimenting with chocolate emulsions also know as "MG chocolate mousse". Here is my last posting on it http://thesensitiveepicure.blogspot.com/2009/01/chocolate-water-chocolate-mousse-little.html which I need to update due to new findings and additional experiments I have yet to conduct.

    This is not a straight-forward emulsion. Beyond the emulsification chemistry, we need to consider the precise processing techniques for a complex medium such as chocolate. One major material consideration you left out is the wax crystal formation. That's one of the aspects I'm working on.

    I was successful in have a stable 50% internal phase of water in chocolate (by weight). gently heated with stirring semi-sweet chocolate chips + water to 190F until homogeneous & smooth. Put into a metal bowl in an ice bath and whipped until thick emulsion formed - about 60F. I took my samples to school for some polarized light microscopy to find that all my samples were actually 3-phase emulsions! Oil-water-oil! Seems to me there may be additional partitioning going on here . . . (They tasted awesomely decadent!)

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  10. Erik - I see you approve your comments. Just a head's up - you have a typo on one of your expert's name. Her name is Shirley Corriher (not O'Corriher). I was fortunate enough to spend last Wednesday evening with her. She is awesome. I blogged about her, too.

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  11. Great post, Erik! Sorry for being late in linking and commenting - the pingbacks did not work.

    If one teaspoon of water makes the chocolate seize, and three teaspoons (= one tablespoon) makes it flow again, and the emulsion invert... that's a pretty narrow interval.

    I wonder how much it varies with the type and composition of chocolate. It could be tested of course, but it would require much destruction of perfectly nice chocolate, and I imagine it is hard to get figures for exactly how much lecithin is in each brand and variety.

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  12. Erin: thanks for the comments and corrections. 50% water w/w is really impressive! How is the texture? I'd really like to see a post on this. I've seen some recent reports of W/O/W emulsions for low fat alternatives (here and here), so I guess decadent is the right word for your O/W/O emulsion :)

    Malin: the use/waste of good chocolate is also one of my concerns, and I guess it's no good substitute using the really cheap stuff either...

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  13. "I took my samples to school for some polarized light microscopy"
    Oh, now I'm really envious. That's one of the things you really don't get to do when you are in the more theoretic/computer based parts of research...

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  14. Awesome Research on chocolate!!
    Will cite you in my research paper :)
    Thanks for showing your sources as well!

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  15. A humorous addition to the conversation - I am an undergrad chemistry major (30+ years ago) and I have a 21 year old daughter who is a Psych major. She asked me this morning why sometimes when she melts chocolate, it gets all grainy. I said it seized and then did a quick internet search to find this article. (GREAT article; very approachable.) I read and explained what chocolate seizing was to her. She started laughing very hard and said "This is the difference between a chemist and a normal person....I asked a question and got a 10 minute answer; I was good with just knowing it was called seizing". The conversation then progressed into a wonderful Saturday morning conversation on things like just what "answers" a question and why people do reseach. Thank you.

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  16. Anonymous: thanks for the nice comment. I've had the same experience numerous times ;) Actually, I guess this is an excellent example of what has been termed "threshold concepts" which I wrote about in "Why are some considered food lovers whereas others are considered food geeks?". This is the same that you might experience when talking with physicists who seem to have and urge to convert everything into mathematics. Or when at the doctor (s)he reacts to your pain with no apparent empathy, but as if the pain was just another a tool for her/him to use analytically as a tool (which it actually is, whereas the nurse has a different role)

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  17. I melted chocolate chips with a dab of shortening to dip coconut balls in, then decided to add a little gran marnier. Well, it seized up. What can I do?

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  18. chocolatamore:

    When chocolate has seized, it's not much to do but to take things in another direction, ...with that specific batch of chocolate, that is. The reason is that all alcoholic drinks contain enough water to seize the chocolate unless you use only miniscule amounts. If you want gran marnier flavour I'd say you have two or three options:

    1) gran marnier in the centre rather than on the outside: dip the coconut balls in, or sprinkle with, gran marnier and let it infuse before covering with chocolate. That way you avoid mixing melted chocolate with a water-containing ingredient. Then the chocolate will still be pure chocolate. If you make another batch all together you might try to incorporate gran marnier in the coconut ball recipe from the start.

    2) Use some additional ingredient that will soak up the gran marnier so the water/liquid doesn't go into the chocolate. Say, you soak some bisquit in gran marnier, let it dry in the oven at low temperature and then add it to the chocolate mixture. You'll lose the alcohol together with the water this way, though.

    3) If you insist on having gran marnier in the chocolate and not the filling/centre, you can convert the chocolate into truffles (making a ganache). I've published a basic recipe for ganache here (swap some of the cream with gran marnier) and a truffles recipe here. The problem in using truffles/ganache for covering is that it'll melt quite quickly in your hands unless you have something that covers it, like ground nuts. An option is rolling them in ground/grated coconut. BTW, that's one reason why couverture chocolate has such high demands in terms of quality (see also enrobing).

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  19. this is going to make for one delicious science project :)

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  20. I still don't understand why the water doesn't just evaporate. I found this blog by googling it after messing up a batch of melting chocolate today, and beforehand I had tried to fix it by stirring it on very low heat for quite a long time, like 15 minutes. The teaspoonful of water that ended up in my chocolate surely should have evaporated by then!

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  21. It's not very surprising, actually, that the water doesn't simply evaporate because it binds to (dissolves) sugar in the chocolate. Hence, what you actually get is a very concentrated syrup mixed with solid sugar. Getting rid of that water is not at all easy, and furthermore it will be distributed inside the chocolate. Imagine that you poured a spoonful of water in your sugar bowl (which is a very relevant analogy; you'd have a hard time "drying up" that sugar again, right?

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  22. Impressive science. Here's a question: why, chemically, does Lindt 85% chocolate seem to seize much more easily than the 70%? And does that suggest that adding some ingredient missing in the 85% could make chocolate less likely to seize?

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  23. Bill: sorry for the late reply. The reason for the delay is that your question is actually a very good one. Basically, dark chocolates usually contain only cocoa mass and sugar, plus a little lecithin emulsifier. Cocoa mass, again, contains 50-55% cocoa fat (cocoa butter).

    Going from 85% to 70% might imply two possible things recipe-wise, and I guess this would be relevant in explaining your question:

    1) 15% of the cocoa mass in the 85% chocolate is replaced by sugar to give the 70% chocolate
    2) 15% of the cocoa mass in the 85% chocolate is replaced by a combination of sugar and cocoa fat to give the 70% chocolate

    (The amount of lecithin emulsifier might also be different)

    Hence, details about the contents might be of help in elucidating this. Your question spurred my curiosity so I've sent an inquiry to Lindt. Hopefully they'll be able to answer and I'll post it here when received.

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