The formula for a longer-lasting soufflé / taro, Thai tea, and green tea soufflés

Lemon soufflé with candied lemon peel

Hey all, I know it's been a while since my last post.  This recent project took a few unexpected turns.  Anyways, I decided this time to focus on soufflés, which are known to be one of the more intimidating baked goods to make.  This reputation was earned in part due to the idea that soufflés will readily collapse, surely ruining whatever dinner party you had planned.  I'm writing this article to hopefully encourage you to give soufflés a chance, as they are a highly versatile and delicious dessert with surprisingly simple execution.

Left: pastry cream, center-left: pastry cream combined with melted chocolate and cocoa powder, with 1/3 of the meringue to be mixed in. Center-right: folding in remaining meringue into pastry cream mixture, right: baked chocolate soufflé

Soufflés have essentially three components, 1) pastry cream, combined with 2) a flavoring element, with 3) a meringue folded in.  This makes the finished product basically a baked pudding, but with the added meringue component allows the soufflé to expand with heat.   My key goals with this dessert were to 1) find a generalizable formula for soufflés that could be customized for whatever flavor desired, and 2) find a way to keep soufflés standing.

A summary of findings and procedure:

1. create a batch of pastry cream 
2. choose flavorings low in water content, like powdered drink mixes or alcohol based flavorings, and mix into pastry cream
3. follow the per-ramekin formula provided below for proportions of pastry cream, flavorings, and meringue
4. stir 1/3 of meringue into pastry cream mixture, then fold in of the rest
5. fill ramekins coated with butter and sugar with soufflé batter to the top, scrape a knife over the top to flatten the batter, tap the ramekin against the counter to release any large air bubbles, and run a fingernail along the ramekin edge to create a lip between the edge of the batter and ramekin
6. bake at ~390 degrees Fahrenheit for 20 minutes

• in the absence of a working oven, soufflés can be cooked in a rice cooker by loading ramekins in, filling water up halfway, and cooking for ~25 minutes, with slightly inferior texture
• to a point, higher temperatures and longer cooking times improve soufflé stability
• lemon juice is known to stabilize meringues, and likewise seems to have an effect stabilizing soufflés, a small amount can be used per ramekin, 0.5-1 tbsp, but will alter the soufflé flavor.  cream of tartar may achieve a similar effect

A generalizable soufflé formula

Creating  raspberry and blueberry fruit flavorings by simmering with sugar and straining to create purees.  Left: boiling lemon peels in first water 2-3 times before boiling in a simple syrup.

I noticed that if I took Gordon Ramsay's chocolate souffle recipe and switched out the flavoring components by volume for fruit puree, the result was delicious, but messy and undercooked.  The obvious cause of this is water content: the flavoring components of a chocolate souffle (chocolate and cocoa powder) each have fairly low water content, while fruit purees have a larger amount of water by volume.  Water as a high specific heat, and must be heated up and vaporized for the protein matrix of the soufflé to set, however, in the meantime all that water is basically boiling the soufflé batter and spilling it all over the place (see above figure).  The key to a generalizable soufflé recipe is then choosing flavoring components with minimal water content.  

Left: combined pastry cream and fruit purees.  Center: soufflé batters added to ramekins coated with butter and sugar.  Right: messy, finished soufflés.  The water content and amount of the fruit flavorings were too high, this can be remedied most easily by using fruit-flavored alcohols or powders for flavor, or  using very small quantities of fruit purees.

I chose to demonstrate this using some of my favorite bubble tea flavors: taro, green tea, and Thai tea, which are each available in flavored powder forms (for green tea, don't make the mistake I did and use real 100% green tea powder, which will end up too bitter and hygroscopic - use the green tea powder mix).  This same strategy can be seen in various other soufflé recipes that call for the use of alcohol for flavoring, since alcohol evaporates much more readily than water.

Left: combining pastry cream with taro puree and taro powder, thai tea powder, and green tea powder mix. Center: ramekins filled with batter prior to baking. Right: Finished taro, thai tea, and green tea souffles.  Note: incorporating 1 tbsp of taro puree per ramekin adds considerable richness and texture to the soufflé.  I highly recommend this flavor.  For green tea, do not use 100% green tea as I did, use green tea powder mix

Formula for a single-ramekin soufflé: 
1/2 cup pastry cream + 2 tbsp low-water content flavoring + 1-1 1/3 large egg whites (with 1 tbsp sugar) worth of meringue.

A longer-standing soufflé

Experimenting with different possible ways of stabilizing soufflés. Left: combining pastry cream with taro puree and taro powder.  Center: combining pastry cream and meringue elements.  Right: finished soufflé batters in ramekins.  The top ramekin contains a small amount of lemon juice, the center contains a higher meringue-to-pastry cream ratio, and the bottom one contains more pastry cream and less meringue

Many recipes online will claim to have a 'foolproof' soufflé, but few bother to explain why this or that formulation actually helps keep a soufflé stable. My initial thoughts were that the key to maintaining a soufflé's height after removal from the oven was to add more structural support, in the form of gelatin or methylcellulose.  These attempts were all met with failure.  Instead, I noticed that if I incorporated large amounts of meringue into my soufflé formulations, I saw more shrinkage of the soufflé as it cooled.  The behavior of the soufflé then is not unlike a cloud of gas, which can be defined by the ideal gas law,

Pressure * Volume = moles of gas * ideal gas constant * Temperature

(or PV = nRT)

Holding pressure, moles of gas, and the constant R constant, the volume of gases/air pockets within the soufflé are dependent on their temperature.  A drop in a soufflé internal temperature from 160 to 100 degrees Fahrenheit would result in a 10% shrinkage of air pockets (a somewhat larger drop in volume is observed since the soufflé air pockets are not gas impermeable - the moles of gas, n, within each pocket is not actually constant and may also drop with time).  While the cooling of the soufflé and shrinking of air pockets is unavoidable, the effects can be minimized by decreasing the meringue composition of the soufflé.  This was factored into the generalizable soufflé formula provided above.

Left: Soufflés immediately after 20 minutes at ~390 degrees Fahrenheit.  Center: Soufflés 5 mintues removed from oven.  Right: Soufflés 10 minutes removed from oven.  The leftmost ramekin contains lemon juice, the center contains more meringue-to-pastry cream, while the right most contains more pastry cream-to-meringue by volume.  The key comparison is between the rightmost ramekins, where the soufflé with more pastry cream had a smaller deflation

I hope this guide helped clear up some questions about how to go about making soufflés, and will encourage you to go out and try to make soufflés of new and interesting flavors! In the future I may post more articles on some more out-there flavors I made, as well as more advanced things you can do with soufflés.