Is it possible to make custard with water?

Wooohooo!! Now THAT’s the kind of super-nerdy question that really kicks a Joe week off right! I thank you for it, reader Denny! The answer is no, you can’t make a custard with beaten egg and water in the way that you can with, say, beaten egg and milk. All that happens when you heat it is, well, egg drop soup. The question is: why?

The answer is because egg protein molecules repel each other. They’re negatively charged and as a result they naturally push away from each other like two same-sided magnets. In order for a gel network to form, those proteins need to attract — or at least not repel — one another as they uncoil. They’re then free to bond with each other side-to-side to create a molecular mesh. That mesh reduces the flow of the water and the result is thickening.

The next logical question is: how is milk any different from water? The answer is: it contains large amounts of minerals — positively charged ions of magnesium, zinc and potassium that become attracted to the proteins, collect on them, and neutralize their negative charges. At which point the proteins can bond. Cool, eh? Salt also works to neutralize egg proteins because sodium ions are positively charged. So add a little salt to your egg-and-water mixture, Denny, and you should have the gel you seek!

Notice that the lemon meringue filling recipe below calls for salt. It too is a mostly-water custard. Lemon juice and egg yolks both have minerals, but I’m guessing probably not enough to create a completely stable gel. The salt probably gives it a little added insurance.

Mm that felt good. Thanks again, Denny!

11 thoughts on “Is it possible to make custard with water?”

  1. The minute I saw the title, I started snorting and snickering fiendishly…I thought I’ll show that Joe Pastry…I had remembered seeing a water-based flan nature on Pierre Herme’s website. I thought here’s my chance to show that Joe his place in the order of things – but alas upon finding a reference to it on some blog (http://bilingualbutter.blogspot.ae/2010/08/weekend-fare-pierre-hermes-flan-leau.html), I discovered, much to my chagrin (and the loss of my grin) that there is some dairy in the filling. I should have never doubted you, Joe, and I suppose it is only fitting that I type these last words with some egg on my face. As luck would have it, the eggs are pasteurized and there’s no chance of poisoning anytime soon 😉 But seriously, Joe – thanks for your tireless effort with this blog 🙂

    1. Yep!

      You can make custards with meat broth since it’s got a lot of minerals, vegetable too depending on the mix!

      Cheers,

      – Joe

    1. Hello Anonymous!

      I think it is indeed the fact that this flan is all yolks. Yolks contain the vast majority of the minerals in an egg, the white being mostly water with some proteins mixed in. This is pretty neat. I’ll have to make it!

      Cheers,

      – Joe

  2. Iiiinteresting. I know you can make custard from egg + non-cow-derived milks so the water seemed almost possible for a second there. In a similar vein I’ve heard that instant pudding needs cow milk but the kind you cook does not. I’ve never tried it, I just use to cooked kind when making dairy-free pudding.

    1. Very interesting, Laura! I’ll have to look into that. I’d think instant pudding would be made with corn starch so it wouldn’t matter, but I’ll check it.

      Thanks for some interesting info!

      Cheers,

      – Joe

  3. It worked! Lovely, light custard–it was already in the oven, definitely not even thinking about holding together so I looked on the every-present internet and found this article. A quick sprinkle of salt and stir, voila! Custard in about 40 minutes of baking.

    You saved the custard pie.

    1. Oh yes, there are ways around it for the truly determined.

      Thanks for the comment, Lucian!

      Cheers,

      – Joe

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