Two Hour Tonkotsu Ramen! (part 2) / emulsified tonkotsu broth

UPDATE (7/28/2015): I have finally gotten around to repeating this recipe (new article coming soon), and can confirm that an emulsifying agent is necessary, and that egg yolks can work (ensure that the broth is at least 160 F to ensure no risk of bacteria) - just temper the egg yolks first with hot broth, then add to broth and use an immersion blender.

Continuing from last time, more on how to make a rich, creamy tonkotsu ramen broth, and the finished assembled product.

Tonkotsu Ramen Broth

Tonkotsu ramen broth can be summed up as a richly pork-flavored broth, with high gelatin content (leaves a distinctly sticky sensation on your lips), emulsified pork fat, and smoky aromatics.  Traditionally, this broth is made by boiling pork feet and chicken bones for anywhere from 6 to 10 hours, in order to break down all the collagen in bone, marrow, and other connective tissue into gelatin (gelatin is denatured collagen, or collagen protein molecules that have become unfolded).  However, as with other cuts of meat high in connective tissue, this process can be expedited using a pressure cooker.

Pressure cookers accomplish this feat by allowing you to braise meats at higher temperatures than what is otherwise possible.  Water boils when the pressure within the water to enter the vapor phase exceeds the pressure exerted on it by the air.  Under normal atmospheric conditions, water boils when it is heated to a temperature of 100^o C.  Any additional heat added to the water serves to push water into the vapor phase, rather than increasing the temperature.   However, a pressure cooker allows you to increase the pressure exerted on the water, meaning the contained water can be heated beyond 100^o C.  Since temperature is a measure of available kinetic energy, this means that on a molecular level, there is more energy available to facilitate the breaking down of bonds within collagen molecules.  What this means for a piece of meat in a pressure cooker is that it will basically see more heat energy than it would under regular boiling conditions, speeding up cooking times.

While using a pressure cooker does let you break down collagen much faster and achieve a high-gelatin broth in about 2 hours, ­­­­J. Kenji Lopez-Alt noted that what comes out of your pressure cooker is by no means a tonkotsu ramen broth – there is strong pork flavor, but it also tastes oily, as there is a layer of separated pork fat on top.  The problem is that within a pressure cooker, the water is for the most part, not boiling.  If you were to take a cross section of a pressure cooker in action, you would see that the water is totally still.  However, using the traditional cooking techniques, the water is constantly bubbling.  Over the course of several hours, the constant agitation helps to emulsify the pork fat within the watery broth.  However, this is only one way to create an emulsion.

Left: Broth strained out of the pressure cooker after 2 hours cooking.  There is a unappetizing layer of fat on the top.  Center: The equipment necessary, an immersion blender and soy lecithin powder.  Right: The fat has been emulsified into the broth.  Some light foam remains at the top, which subsides after a minute or so.

As you may know, fats and water are basically immiscible, or they do not mix well.  You can see this in some salad dressings, where the oil will separate out into a layer on top of water-based components.  To remedy this, people will either shake up the dressing before using, or they will introduce an emulsifier, like egg yolk.  Emulsifiers are molecules that can form favorable interactions with both water and fat-based molecules.  These interactions support the formation of a stable, homogeneous mix of fats and water.   By introducing a small amount of soy lecithin powder (~1.5 tsp for ~5 quarts broth), and mixing using a immersion blender, I was able to achieve a lighter broth that did not have a separated oil layer and had a taste much closer to that of a true tonkotsu ramen broth.  Fyi, lecithin is one of the main emulsifying agents in egg yolks, so I imagine this could be done with regular egg yolks. However, you would need to do this at a low enough temperature that the egg yolk wouldn’t coagulate due to heat from the broth (thanks to my research into egg boiling, I can say that the broth would need to be <148^o F).

For the condensed recipe (in part borrowed from J. Kenji Lopez-Alt, with modifications), check out my recipe pages for tonkotsu ramen broth, marinated soft boiled egg, and braised pork belly.

Pretty much every component can be made in advance and reheated as necessary.  The broth will solidify in the refrigerator (since it has high gelatin content), but can be microwaved or reheated on the stove.