custard science -- curdled crises

[lamington]

Hi folks. I have two recipes for custard tarts cooked at relatively high temperatures, but the custards contain no starch and they always curdle. The custard is not *meant* to curdle, but given the ingredients and temps, I expect them to! I'm using a gas oven, and have tested that temp is correct on the top shelf (have also tried middle shelf placement and temperature).

So I'm wondering whether there is some magic trick that I don't know, or if the recipe writers just ... um ... never tried their own recipes?

Each small tart contains 20-30ml of custard.

(1) 5 yolks + 4oz sugar + 3/8pint double cream

I don't know if this is a US or UK pint, so it's 177-213ml. Double cream is approx 48% fat, I believe. Method: stir everything together in double saucepan until the custard coats a spoon lightly. Cool to room temp. Then pour into cases and bake. Cook at 400F/205C for 20 mins.

(2) 9 yolks + 135gm sugar + 500ml cream (unspecified type)

Method: as above, except the custard isn't cooled before baking. Cook at 'hot' until 'browned on top'. The problem here is that the pastry needs to cook, and that takes at least 10 minutes.

Is the only solution to add a starch?

[Suzanne]

First of all, if the recipe calls for double cream, it's got to be UK; we don't have anything like that generally available here in the US

My guess is that if you cook the custard longer on the stove top, so that the eggs are more fully cooked, they'd be less likely to curdle in the oven. But then, if they're already fully cooked, then they won't solidify in the tart. I'm lost.

And I hate to tell you, but no, they don't always test the recipes.

[kuan]

Prebake the crust. Don't put it in the top shelf. Use a lower temp like 160C. The custard should still be jiggly when you take it out of the oven, a little like a firm jello.

Kuan

[Jock]

Double cream is about equivalent to "Manufacturing" cream or heavy cream here I think. Whenever I cook back home, I use double cream when I would use heavy cream here.

I would be tempted to add a little corn starch (corn flour to you Lamington ) to stabalize the custard a little. Make it more like a pastry cream. Then as Kuan said, prebake the crusts which will also help eliminate that pale, slightly guey bit where custard meets pastry in the bottom of the tart.

Jock

[lamington]

Thanks folks! There is one important aspect of this question, Jock and kuan: the cooking method (temp, no pre-baking of pastry) *cannot* be altered. I know that the traditional versions of these tarts are cooked successfully at temperatures at least as high as those described. The only issue is the recipes for the custards -- so the problem-solving is all about the issue of curdled custard, and unreliable recipe writers

I make a mean traditional Anglo custard tart, but that's not the goal here, I'm afraid, so no gentle cooking and lovely just-set custard with nutmeg sprinkled on top

[miahoyhoy]

Temp and method are the ways to alter the final product. Without changing those I'd say use less egg. Like take 1 yolk away. But still it is said that heating the mixture (without starch) above 85 or 90 C will cause it to curdle.
lates,
Jon

[scott123]

This is pretty tricky stuff here - curdling that cannot be controlled by manipulation of heat. Yikes! That being said, here are a few ideas that might apply:

How fresh are your ingredients? Experience has shown me that the fresher cream is, the less likely it will curdle.

How consistent is your oven temp? Even though the temp may be "correct" at 400, is it consistently 400 does it vacillate around that?

Also, the phrase "coating the spoon lightly" might allow for some room in terms of interpretation. Like the previous author recommended, try cooking it longer on the stove.

And lastly, you've tried the medium and top shelves, why not give the bottom shelf a try? If the custard goes into the pastry cooled, the intense bottom heat will cook the pastry faster.

Good luck!

[lamington]

thanks for those scott123! Some excellent ideas, which I'll have a play with. If success is had following everyone's contributions, I shall report back.

[Suzanne]

Lamington and I have been discussing cream, and he came up with a question that I think others might be interested in discussing:

I'm curious... so 'heavy' and 'manufacturing' cream are inferior products compared to double cream?

Here's what I can find, for generally available cream here in the U.S.:

Heavy cream (aka whipping cream) is 36 to 40 percent butterfat, although what one gets in the grocery is usually at the lower end of the range; 40 percent is more likely to be found only commercially.

Manufacturing -- ?? Jock, can you give us more information?

French crème fraiche is at least 30 percent (but that is slightly fermented); crème fluide is unfermented, for whipping, at about 35 percent (although I'm not sure this is easily found in the U.S.).

English Double cream weighs in at around 48 percent fat; clotted cream can go up to around 60 percent.

SO: what does everyone think about lamingon's question?

[lamington]

Originally posted by Suzanne

SO: what does everyone think about lamingon's question?

Oh, I hope i'm not being set up for "it's a silly question"!

In case anyone is interested, cream in Australia is generally either 'whipping cream' at approx 35% fat, and almost always containing a little gelatine, or 'thick/double cream' which ranges in fat content from about 45% up to 60%! All of a sudden i can't remember if we have an equivalent to 'single cream' (in Europe typically either side of 20%)... if we do then it's a relatively recent innovation here.

[Suzanne]

I'd never intentionally set anyone up, dear. And anyway, I never, ever consider discussions of ingredients to be silly. I love learning about food!

I didn't even go into the lighter stuff -- "half and half" (10 to 12 percent fat) which seems to have replaced what we call "light cream" or "coffee cream" or "table cream" (18 to 30 percent; generally about 20).

And then there are all the UHT (ultra-high-temperature/ultra-parteurized) versions, which taste cooked. To me those are definitely inferior, because they are made for the convenience of the producer, not for the taste of the user.

[lamington]

Originally posted by Suzanne

And then there are all the UHT (ultra-high-temperature/ultra-parteurized) versions, which taste cooked. To me those are definitely inferior, because they are made for the convenience of the producer, not for the taste of the user.

Go tell it to the Germans! Many traumatic Kaffee&Kuchen events were spoilt by the presentation of the poisoned chalice of 'Kaffeesahne' (coffee cream) or even 'Luxuskaffeesahne' (luxury...) all of which were either UHT abominations or, worse still, vegetable fat products. Can't they taste the horror?

And the French do a depressing job of wheeling out the UHT too.

[scott123]

Ultra Pasteurized Cream is an abomination *shaking my head* The sacrifices humanity makes in the name of food preservation. I have to go to such great lengths to find non ultra pasteurized cream. The most frustrating aspect of this "food preserving" process is that it's totally unnecessary - the non UHT stuff I buy lasts for months! ARGHHHH!

[Nick.Shu]

lam, 2 possible schools of thought here.

1st is to blind bake the crust and cook out the custard on the stove and then add to the cooked bases.

2nd is to review the amount of sugar in the recipe. From what i remember in theory, the sugar in the recipe also helps retard the curdling of the eggs by raising the cooking temp of the yolks from about 62 degs to about 82 degs.

Given this, you may partially blind bake the crusts, and finish the tarts at a lower temp.

oh yeah, standard oven or fan forced?

Nick

[Bryan Blinstrup]

When I make custard, creme anglaise, or ice cream I follow the same basic method. All three are very similar considering that the ingredients are eggs, sugar, and milk or cream.

1. Bring the cream to a boil in a pot.
2. In a mixing bowl, whish together the yolks and sugar. (Make sure to mix them well, or the sugar will dry out the yolks)
3. Slowly pour the cream into the mixing bowl and whisk until the egg and sugar mixture is incorporated.
4. Return the cream, eggs, and sugar to the pot and cook to nappe*.
5. Once the mixture has reached Nappe, pour it into a clean mixing bowl over an ice bath and stir lightly until cooled.
6. Once cool, the custard micture is ready to use (Bake).

*Nappe is a measure of sauce thickness. It is determined by stirring the sauce with a wooden spoon and then running a finger across the back of the spoon. If the sauce down, the sauce is not yet to nappe, if the sauce holds it's place it is at nappe.

If this method does not work, the ingredients can also be cooked over a bain marie, or double boiler. the double boiler method takes a much longer time, but it is easier to control due to the low heat involved.

1. Whisk together eggs and sugar, then add the cream.
2. Bring water in the bottom section of the double boiler to a boil, and add eggs, cream and sugar to the top section. Make sure that the water does not touch the top section.
3. Cook to nappe, stirring the entire time to prevent the eggs from coagulating.
4. When the mixture reaches nappe, cool it in a bowl over an ice bath.

The ice bath is a vital step in these processes because it stops the eggs from overcooking. Overcooking your eggs will always result in curdling the custard.

Also, try placing the custard pan in a waterbath (a larger pan filled with hot water.) This insulates the pan and assures that the eggs reach the proper temperature slowly, preventing curdling. The water should reach about one-half to three-quarters of the way up the smaller pan.

Hope this helps,
Bryan