Sunday, November 29, 2009

Liquid Nitrogen

Liquid nitrogen (LN2) is really, really cold. Water boils at 212 F, LN2 boils at -320 F.

Its ability to instantly freeze liquids is ideal for ice cream making. Traditional ice cream is made in a batch freezer. Ice cream base (dairy, flavorings, stabilizers) is placed into a cylindrical freezer whose edges are cooled to 22 F. Water in the base freezes and the ice crystals are scraped from the walls by metal blades. When the base becomes the consistency of soft-serve, it is removed and placed in a colder freezer to harden.

Smooth ice cream is achieved by forming the smallest ice crystals possible in the shortest amount of time. LN2 does this by freezing the water molecules on contact. There is also no overrun (air) added to the base, so the resulting ice cream is extremely dense.

To make ice cream this way, simply prepare an ice cream base of any flavor (without mix-ins, they would become rock hard) and place in a large metal bowl. While stirring with a wooden spoon, slowly add liquid nitrogen. Keep adding until desired consistency is reached--it will usually take between three and five liters.

Example: At the Fat Duck, chef Heston Blumenthal serves Bacon and Egg Ice Cream (made using liquid nitrogen) atop caramelized french toast.

**Always be extremely careful while handling liquid nitrogen. However, for a neat party trick, dip your fingers in a bowl of liquid nitrogen for a second or two. The temperature of a human hand is so much higher than that of the LN2, that your fingers will create a pocket of steam in the LN2, and you will not be harmed. This only works for a couple of seconds, so don't get carried away.

Sunday, November 22, 2009

Xanthan Gum

Xanthan gum is a polysaccharide, meaning it is composed of several sugars linked together. Its structure makes it ideal for thickening, stabilizing, and emulsifying.

When a very small amount is added to a mixture (on the order of 1% by weight), the mixture gains pseudoplasticity--it becomes very viscous, and retains that viscosity when shaken, stirred, heated/cooled. Pseudoplasticity is what gives a bottle of Heinz ketchup its impossible-to-pour quality; without xanthan gum, we would either buy ketchup as thin as water, or as thick as peanut butter.

In the kitchen, xanthan gum can be used to stabilize a foam. By pureeing any fruit or vegetable and blending the liquid you can aerate it enough to create a foam, but without a stabilizer the air bubbles will rapidly deflate.

The appeal of a foam is flavor. Any foam can be added to a dish, imparting its flavor but not physically affecting the dish in any way. Once eaten, the foam "disappears", imparting only its flavor.

To make a foam, combine any amount of fruit juice, vegetable puree, or any other liquid, with .5% by mass xanthan gum. Whip with hand mixer or in blender until desired consistency is achieved.

Example: At WD~50, chef Alex Stupak tops a dessert of braised pineapple and mustard ice cream with a coconut foam.

Saturday, November 14, 2009

Rotary Evaporation

Necessary? No. Awesome? Yes.

Rotary evaporators are used to distill solvents. Distillation is the process of separating a mixture into its components based on their volatilities (how easily they vaporize). This is done by evaporating and condensing the solvent.

A solvent is placed into the evaporation flask. The vacuum is used to greatly reduce the boiling point of the solvent. This allows the solvent to vaporize just above room temperature--higher temperatures would destroy the flavor and aroma compounds. As the solvent evaporates it travels into the condenser where it re-condenses (big shock) and drips into the receiving flask.

So now you're probably thinking, how the hell would this process apply to a restaurant kitchen?

Say you were making a dessert and wanted a sauce made from blood oranges.

By running freshly squeezed blood orange juice through a rotary evaporator, you could remove the water from the juice. Left in the evaporation flask would be a thin syrup, the "essence" of the blood orange juice. Using this syrup to make your sauce would result in a product that was more "orange-y" than anything you could achieve by reducing blood orange juice on a stovetop.

Example: At the French Culinary Institute, Dave Arnold uses rotary evaporation to make the "perfect" gin and tonic. He uses the evaporator to make concentrated lime juice and distill his own gin (flavored with any aromatic conceivable). Arnold even does away with the Schweppes and injects CO2 straight into the drink.

Tuesday, November 10, 2009

Tapioca Maltodextrin

Tapioca maltodextrin is a modified starch that thickens and stabilizes fatty compounds. It is produced from tapioca starch and comes in the form of a white powder. Maltodextrin has been used for some time as a fat-substitute in commercial products because it is easily digestible (similar to glucose) and retains its properties when frozen/thawed.

In the kitchen, tapioca maltodextrin can be used to bind fat and turn any high-fat ingredient into a powder. Upon consumption, the powder immediately reconstitutes in the mouth. This technique is usually applied to desserts (peanut butter, nutella, marshmallow fluff). However, it can have savory uses (bacon fat, foie gras).

When using tapioca maltodextrin, fats should be liquified, chilled, and combined in a starting ratio of 60% fat to 40% maltodextrin. The mixture should be blended and passed through a tamis (or sieve).

Example: At Grant Achatz's restaurant Alinea, caramel powder is made by combining crushed caramel and tapioca maltodextrin. The powder is served in a shot glass, garnished with salt.