One of the concepts often overlooked in the baking industry is that baking is really fundamental chemistry in action. Yes, we use ingredients that are on every home cook’s pantry shelf and yes, we manipulate those ingredients to produce a wide variety of cookie products. Not only do we change the ratio of flour to sugar to fat, but we add chemical ingredients such as sodium bicarbonate (baking soda) and leavening acids to produce desired, controllable results.
The fundamental chemistry, if misused or not followed properly, will have a great effect on the process and finished product results. Not weighing correct amounts, using the wrong chemicals, incorrect order of addition, incorrect processes, and using the wrong heat levels during baking all can affect the finished product and subsequent shelf life.
Let’s use a simple sugar cookie dough as an example and explore what happens during the process with two basic ingredients: sugar and sodium bicarbonate. Following the proper recipe and procedure is a given. Adding the right ingredients to the mixer in the right order should be a process that is unchangeable and should be altered only under strict supervision and only when necessary.
Most mixers use mechanical force to whip air into the solid fat portion of a sugar cookie recipe as the sharp corners of the sugar crystal tear into the fat, leaving a trace of air and forming the micro-cells needed for future gas absorbing sites and subsequent expansion when heated in the oven. The water used dissolves other water-soluble ingredient compounds, but only to the extent that the water solutions become supersaturated and cannot dissolve anymore solids.
A good example of this is the sugar in a dough for a rotary molder. A good rule of thumb is to have about one-third of the total dry sugar in formula remain in solid form. This solid sugar helps the rotary feeding gauge rolls grip the dough and force the dough into the moulding cups. If too many sugar crystals remain (due to a lack of formula water), you have a coarse, crumby dough that either is hard to machine or cannot be machined (it’s usually best to discard the dough at this point—trying to remix with additional water is usually too late in the process to be worthwhile). The remaining sugar crystals in the dough, even after moulding, helps in the extraction from the moulding cups by the extraction apron. Some bakeries “wet” the apron with steam or water to lightly dissolve the surface sugar so the surface dough is sticky, assisting in pulling out the dough of the moulding cup.
Various chemical reactions take place during the mixing process. Sodium bicarbonate, or baking soda, is usually in the formula and is considered as part of the leavening system. Fundamental chemistry occurs when adding baking soda to the mixer. The sodium bicarbonate neutralizes the acidic ingredients (including high-fructose corn syrup, buttermilk, some flavors, etc.) producing carbon dioxide gas for cell formation. If there are no micro-cells from the mechanical mixing, there is no place for the gas to go, thus producing a tight or unmachinable dough. Even the flour itself has a pH of 6.5–6.9 and requires neutralization. Having excess sodium bicarbonate levels is a desirable attribute in a recipe that contains chocolate or cocoa.
Sodium bicarbonate neutralizes some of the acid ingredients and creates air cells, but leavening acids also react with the baking soda to produce micro-cells. Single-acting baking powders do this in the mixer. Double-acting baking powders have acids to react in the mixer, but additional acids with heat-activation properties react in the oven, providing lift and aeration. This is the “oven spring” or lift in the first zone of the oven.
As the dough moves onto the panning belt and then to the oven, the initial temperature of dough is roughly 75˚F (24˚C) or cooler (especially if the dough has chocolate chips). The first zone begins the baking process by melting the remaining fat crystals and heating the water portion of the dough, allowing more water-soluble compounds to dissolve at around 100˚F (38˚C). As the dough proceeds further into the oven and the moisture evaporates, the super-saturated solution recrystallizes, building the structure of the cookie.
After leaving the oven and cooling under proper conditions, the sugar solidifies into a matrix-linked web-holding structure, thus holding the cookie and added items (nuts, chocolate chips, etc.) in place. It also gives the consumer the desired textural attributes that they expect. Adding excess sugar to a formula will harden the finished product. Adding syrups (whether corn syrup, high-fructose corn syrup, honey, etc.) yields a softer bite. Adding excess sodium bicarbonate will raise the finished pH, thus driving color pigment formation (along with the stable color pigments that will last during shelf life) and contribute to the flavor in cocoa-based cookies.