Gratin Potatoes, a curdled tale

I just spent the last hour making a potato gratin, and as it bakes, it's curdling.

With guests arriving in less than ten minutes, I'm trying to believe this isn't a bad thing. I want to celebrate the curd. I want to love that what I'm bending over right now is steaming layers of satiny potato, crunchy crisp on top, held together by a tenuous curd and hiding a shallow bath of... whey.

But I so wanted some creaminess tonight.


I obviously don't make potato gratin often enough. And actually, I feel a little stupid because I should've known this would happen. I'm in Belfast for the weekend, and I couldn't find any organic cream at the markets, so I used a lovely local organic milk instead. I figured I'd flavour the milk with thyme and garlic and let it reduce on the stove a little to intensify, before adding it to the potatoes. But I forgot that milk is much more likely than cream to curdle when it comes in contact with anything acidic. Anne Mendelsohn's gorgeous book on milk explains why, and when I get back to Berlin (I'm in Belfast for the weekend), I'll look there to find out exactly why this is so. From what I remember it has something to do with the way the fat in cream prevents acid from coagulating milk proteins. If I'd stabilised the milk in some way, by adding flour in the form of a roux or beurre manie, things would look a little creamier right now. (If a tad stodgy: I prefer to save flour-enriched sauces for less starchy vegetables, like cauliflower).
I think the acid came from the caramelised onions layered through the gratin. I'd been so pleased (perhaps a little too pleased) with this addition; with their deep caramel jaminess as a counterpoint to an unctuous creamy base.

To be sure, the gratin still tastes good. I've been taking it out of the oven a little too frequently, tasting it, hoping it'll uncurdle (that's ridiculous).

Tasty at it is, I'm anxious the curd might put my guests off. There's something abject about them. We don't mind curds pressed into a form (like paneer), but floating around, unbounded, they're reminiscent of the regurgitated (like baby's vomit, which is also caused by acid).

Sitting here writing this post a mere 5 minutes before my guests arrive, I realise I'm writing a disclaimer. I do this when dishes don't turn out right. I'd prefer to be the one to name their faults, then to risk their naming by my guests.

Or worse, their silence!

Would it do to recall a dish that flagrantly curdles? An Italian pork braise that The River Cafe Cookbook offers a rendition of. In this simple dish, pork loin is cooked in milk, garlic, lemon peel and sage, until meltingly tender. The milk curdles a rich golden and the whey is mostly simmered away.

For this pork to be left without a creamy sauce seems appropriate. But my gratin potatoes? They, and I, are still longing for what is now lost and I will start all over again with my favourite local cream once I'm back in Berlin.


Recommended Reading:
Rose Grey and Ruth Rogers, The River Cafe Cookbook, Ebury Press, 1995.
Anne Mendelson, Milk: The Surprising Story of Milk Throughout the Ages, Knopf Publishing, 2008.