Creme brulee - how and why?

[Nich]

How and why does a creme brulee work?  I had always been taught that custards are done when they're about 80c (176f) - much over 83 (181f) and they risk splitting.  I understand that ingredients other than egg will change this a bit, but I have trouble trying to quantify it so I'm not reliant on any specific recipe.

There's a nice table in modernist cuisine (Book 4, somewhere around pagge 84 I believe) that, under creme brulee (as in, achieving that texture), it suggests that 30% egg be used at 83c (181f), 50% egg at 80c (176f), and 90% egg at 75c (167f).  Which is great, except it seems other things impact.  For instance, I've cooked anglaise out to 83c in the past and it was fine but not quite thick enough until I held it there for another 10-15 minutes.  Sometimes lemon curds will set at that temperature and other times they will refuse.

What is it that makes a baked CB set firmer than one cooked either on a stove or sous vide (assuming they're all cooking to the same internal temperature)?  Is it just a bit of dehydration/reduction?  Is it the lack of stirring/agitation that lets the proteins bond differently?

Does it matter if the cream (and/or milk if you're that way inclined) is heated before tempering into the eggs, rather than blending to a homogeneous mix and then heating?  Does passing post-cooking destroy some of the bonding created during the cooking that provides thickening power?

To avoid vanilla seeds sinking to the bottom of the ramekin, is it best to let the temperature of the mix cool down, a la pannacotta, so it better suspends in a more viscous custard?

I had a read through a couple of creme brulee threads on here and there is just so much conflicting advice, even as far as whether to use a water bath when using a convection oven; to use a low temp (or boiling) steam oven; or whether the mix should sit overnight (cooked or uncooked) before setting in dishes.




Some background/context:

I've just started at a new kitchen, and the former pastry chef just left.  No handover or exchange of recipes.  We each in the kitchen have recipes we've used in the past that work, but the pastry oven, for whatever reason, has no control to lower or even disable the fan.  The force of the air leaves a (thin) set foam that looks unpleasant but is hidden by the caramel.  

There are two other ovens in the kitchen but they're frequently used.  My preference would be to cook it in a pot (pastry has it's own induction 'hotplate'), but I feel that'd tie up too much time stirring it.  There's a single sous vide waterbath that's used for other things, so it'd be asking a lot to comandeer that for a couple of hours needed to get it up to temp and then cook the custard.  Today I tried to cold-blend the mix, vac-seal it and put it into an empty oven set to 'steam' at 84 degrees (which seemed a tad too  hot to me, but was the temperature another pastry person said they'd used in the past in a pot on the stove), but I was told it came out lumpy.  I wasn't there to see if passing/blending would salvage it.

Really really would prefer to not use the 'Thermomix' recipe, despite it seeming to work - mostly because it seems to be too high a temperature (85c) and yet still seems to come out smooth (and also because professional pride and learning opportunities).

For reference, after looking over MC@home and Advanced bread and pastry, and comparing recipes other chefs (and myself) have used successfully in the past, it looks like the egg:cream ratio varies from 21 to 40%.  The recipe I did a test batch with was 28% (that's 4 yolks and 1 whole egg to 500g of cream; a variation I also tried (less sugar, seemed to let the nutmeg shine better) had 7 yolks to 500g of cream.  I don't think it was the recipe(s) that was the problem.

 

[pastrygirl]

Yes, stirred custards cook differently from baked/undisturbed custards.  Do you have McGee's on Food and Cooking?  I'm pretty sure agitated vs still egg cookery is covered in there.

[Lisa Shock]

McGee covers water baths in detail, and the stirred vs 'still'. There are a lot of variables in cooking custards. You could solve your issue by placing a sheet pan on top while baking, either up or down, whatever works, it would still allow evaporation of the water but would leave the tops undisturbed.

[Nich]

Thanks, I totally forgot to check McGee, it answered a few of those questions.