BUTTER SAUCES
BUTTER SAUCES ARE THE SIMPLEST AND SOMETIMES the most delicious embellishment to a piece of steamed fish, some grilled seafood, or poached chicken. This chapter focuses on brown butter (melted butter cooked until nutty brown) and white butter, or beurre blanc (cold butter emulsified into a white wine and vinegar reduction).
To makes these sauces successfully, it helps to understand some butter science. Simply put, butter is overwhipped or churned cream. In cream, globules of fat protected by a phospholipid membrane float about in a suspension of water. When cream is agitated, or churned, the fat globules collide with one another, causing the membranes to break. The freed fat globules then begin to clump together, trapping little pockets of water along with the broken membrane pieces and some intact fat crystals. After the cream is churned into a semisolid mass of butter, any remaining liquid is drawn off as buttermilk. So what begins as an oil-in-water emulsion known as cream is reversed to a water-in-oil emulsion known as butter.
All butter must consist of at least 80 percent milk fat, according to U.S. Department of Agriculture standards. Most commercial butters do not exceed this. (Some European butters and Hotel Bar's Plugra are exceptions, containing from 82 to 88 percent milk fat.) All butters contain 2 percent milk solids, and the remainder is water.
BROWN BUTTER SAUCE
Brown butter sauce is simply melted butter that has been heated long enough to cause the water to evaporate and the milk solids and fat to develop a nutty brown color and flavor. The key to this sauce is cooking the butter long enough to create that nutty flavor and color without causing the solids to burn. Seconds matter when making brown butter.
We started our tests by making brown butter in a small (8-inch) skillet and a small (1-quart) saucepan. The skillet was more challenging because its wide bottom caused the water to evaporate and the solids to brown more quickly. Everything happens a bit more slowly in a saucepan and is easier to control. It's much easier to watch milk solids change color in a shiny saucepan.
Recipes call for melting and cooking the butter at various temperatures. Although there is a moderate risk of burning the solids when cooking over medium heat, lower flames often failed to color the liquid, and the sauce consequently failed to develop its defining "nutty" characteristics.
We wondered just how far you could take brown butter before it would burn. Tests showed that if you stop the cooking process as soon as the solids turn light brown, the liquid itself is still yellow and lacks a nutty flavor. When you allow the solids to turn a deeper brown, the liquid shifts in color and flavor to the "nutty" stage.
Purists strain the finished sauce through cheesecloth to remove darkened milk solids. The solids do look unappealing, and we prefer to leave them out. A simpler approach is to let them settle and carefully pour off the liquid, leaving most of the solids behind.
Plain brown butter is bland and needs some seasoning. A little acid significantly enhances the flavor of the finished sauce. We prefer white wine vinegar, but lemon juice makes a delicious variation. We found that adding the acid as soon as the butter has browned sufficiently is dangerous since the sauce can splatter onto the cook. By waiting just 90 seconds you can minimize splattering without letting the butter sauce cool too much. Salt and a dash of pepper round out the flavors of this simple butter sauce.
WHITE BUTTER SAUCE
White butter sauce is a bit more complex but still easy to execute. It is similar to Béarnaise sauce, but without the egg yolks. The idea is to create an emulsion with butter and a reduction of flavorful ingredients, usually white wine and white wine vinegar. The goal is to get the butter to soften into a cream so that it forms an emulsion rather than melting to liquid fat and separating. The reduction infuses flavor into the sauce and provides the liquid necessary to emulsify the butter.
Dry white wine, white wine vinegar, salt, and pepper are standard ingredients in the reduction for white butter sauce. A few recipes call only for vinegar, or only for wine, but we quickly dismissed these as tasting unbalanced. In the end, we preferred a reduction made with 3 parts white wine and 2 parts white wine vinegar, with some shallots, salt, and pepper added for flavor.
Some sources suggest reducing these liquids until they have almost evaporated. We found that the sauces prepared with more reduction liquid were more stable and airy. For this reason, we suggest reducing the wine and vinegar by two thirds, but no further. Some sources quickly reduce the liquid, but we found that slow cooking provides for a blending of the flavors and gives the shallots more time to soften.
The biggest challenge when making white butter sauce is incorporating the butter. Some sources argue that the butter should be at room temperature when added to the reduction, while others call for chilled butter. Sources also disagree on how the butter should be added (in small increments or all at once) and on whether the pan should be on or off heat.
Making the sauce off heat failed—neither cold nor room-temperature butter softened. Clearly, the pan would have to be over the flame. We then tested the addition of cold butter in increments over very low heat. These tests worked, but it took 8 to 10 minutes to incorporate all of the butter. Adding room-temperature butter in increments over very low heat reduced the time needed to incorporate the butter to 6 or 7 minutes, but the whisking was still tiresome. On several occasions the sauce broke, probably because we slacked off from the constant whisking.
At this point, we turned to a technique advocated by Jim Peterson in his classic book Sauces (Van Nostrand Reinhold, 1998). He keeps the pan over high heat and adds all the butter at once. This method proved easy (it takes less than a minute to whisk in the whole stick of butter) and foolproof, with three caveats.
First, you must use cold butter. Room-temperature butter overheats with this method and the sauce will separate. Second, you must whisk constantly. Third, we found it best to whisk a tiny bit of heavy cream into the reduction before adding the butter. The liquid and acid in the reduction and the water and milk solids in whole butter can successfully emulsify the fat in whole butter. However, some sauces broke when made with only the reduction and whole butter. Our tests showed that heavy cream acts as an additional emulsifying agent. It helps to start emulsification and helps to stabilize the sauce. Our tests showed that without heavy cream the sauce is at greater risk of breaking, especially when the high heat method of adding butter is used.
One final warning about white butter sauce: Make sure that the sauce never reaches a boil, or it will break. If the sauce does break, we have found that the best approach to fixing it is to put 3 tablespoons of heavy cream in a small heavy-bottomed saucepan and reduce it by half over high heat, about 30 seconds. Off heat, vigorously whisk the cream into the broken sauce. Because the sauce loses some of its delicate flavor and texture with this added cream, it's best to whisk constantly at the outset as the butter is added to prevent the sauce from breaking in the first place.