December 1, 1994
Restaurant chefs consider making sauces an art. Creating sauces for large-scale commercial applications is an art too, but one that relies as much on formulating for functional characteristics as it does on pleasing the palate. While no one would call the creation of a good Béarnaise or Bordelaise sauce easy, making those sauces stand up to typical commercial abuse takes more than culinary skill. It requires careful consideration of the functional gauntlet these products must endure, and identification of processes and ingredients that will provide a satisfactory product to the consumer.
"When you think of gravies and sauces, the initial reaction is that this is pretty simple stuff, but there are a lot of issues to address," observes Mike Augustine, manager of food ingredient applications at A.E. Staley Manufacturing Co., Decatur, IL. "There are quite a few things to look at: the kind of finished product you want, what it goes through to get there, and what is put into the formulation."
Foundation in stabilization
Sauces vary in texture, flavor and end use. Some are for dipping, some for use as glazes, and others for application on pasta, meat or vegetables. Sauces can act as fillings. toppings or marinades.
Whatever the format, the one thing sauces share is a high moisture content. When designing a commercial sauce, control of this water is key to a successful product, and this requires careful selection of a stabilizer system.
Stabilizer systems usually consist of starches and gums, but also include emulsifiers for sauces containing fats. While starch is the main viscosifier in sauce applications, gums are frequently used. They can be used alone or in combination, depending on the performance required and any cost constraints.
All stabilizers are not created equal. They have strengths, as well as limitations that proscribe their use. Because choosing the right stabilizer system can make or break the sauce, it is crucial to look at all functions and characteristics needed.
"The first consideration is defining what the product developer is trying to achieve in the finished product," says Jane Gottneid, senior scientist, American Maize-Products Co., Hammond. IN. "Then, to select the proper starch you need to evaluate the effect of formulation, process – including time temperature and shear – storage time and temperature, product reconstitution, and finished product requirements."
Building the formulation
The first set of challenges revolves around the formulation. One of the major factors is the pH of the system. Many sauces are considered low-pH, high-acid products, particularly those based on tomato or vinegar, or those formulated for less severe heat treatments such as hot packs. While this pH may limit microbial growth, it also adversely affects many of the stabilizers. A low pH will promote acid hydrolysis and break down the stabilizer, especially as time and temperature increase.
A low-pH sauce requires a stabilizer that resists acid hydrolysis. With starches, a chemical modification called crosslinking increases the acid stability; the more crosslinking, the more stable the starch. The problem with using some highly crosslinked starches is the same structure that makes the starch granule resistant to abuse slows the swelling process during hydration.
Many of these starches will actually require abusive conditions such as extended exposure to high heat or low pH to fully hydrate the starch granule. As a result, these starches tend to provide less viscosity.
"When you crosslink for process tolerance, the degree of stability in food systems is due to the extent of crosslinking rather than a particular crosslinked product," observes Gottneid.
When using gums, xanthan gum typically provides the best acid stability. Methylcellulose, locust bean gum and guar gum can withstand acidic conditions down to a pH of 3.0. Microcrystalline cellulose can be used, but protective colloids are required for a pH below 4.0, according to Brian Hausner, Avicel food product manager, FMC Corp., Food Ingredients Division, Philadelphia. Gums that do not demonstrate acid tolerance tend to precipitate out at a low pH.
"The salts present have a strong effect on the solubility," observes James Carr, Ph.D., technical director, Sanofi Bio-Industries Inc., Waukesha, WI. "Calcium salts can affect alginate, pectins and certain carrageenans. The presence of chelators would buffer out ions and make them less available to interact with the hydrocolloids."
A number of other ingredients affect the performance of hydrocolloids. Fats and soluble solids like sugar or salt can inhibit the hydration of starch and hydrocolloids. Some believe the fat coats the starch granule, preventing water from reaching the starch. Others note the possibility that the fat may complex with amylose-containing starches.
Other hydrocolloids present in the system also can compete for the available water needed for complete hydration. Some ingredients may contain amylase, an enzyme that can break down starch. Gottneid lists flour, improperly blanched vegetables and spices among the potential amylose-containing culprits frequently used in sauce formulations.
Synergies exist between certain gums and also with starch. For example, combining xanthan and locust bean gum increases the viscosity to a greater degree than expected with either of the gums used singly. A synergistic effect can be good if you use it to your advantage by finding the appropriate combination and reducing the total amount of stabilizer required.
Naturally occurring proteins in other ingredients – like casein in dairy products such as cheese – can denature with the application of heat, providing additional viscosity. On the other hand, proteins may adversely interact with some of the negatively charged hydrocolloids under acidic conditions.
Assembling the process
Because so many aspects in the production of sauces affect the performance of the stabilizers, processing must be closely examined first in terms of the procedures that have the greatest effect: shear and temperature. In some cases, the net effect is disruption or destruction of the stabilizer. In others, subjecting the stabilizers in a sauce to such stress only temporarily affects the sauce's rheology or flow characteristics.
Heat is especially destructive to starch, particularly those types without crosslinking. As the temperature and time of exposure increase, the starch granule swells until it fragments, loses viscosity and creates a long, stringy texture.
Most gums are heat-thinning. but will regain viscosity to a certain extent once cooled. Guar is probably the most sensitive to heat and may be destroyed under retort conditions. Methylcellulose has the opposite reaction to heat; the hotter it gets, the thicker it gets.
Almost all sauces require a cooking step for microbial control, stabilizer functionality and flavor development. The methods can range from a steam kettle cook and subsequent freezing or hot pack – a relatively mild treatment in terms of the stabilizer -- to retorting, to aseptic processing.
"In an aseptic process, starches are the main stabilizer," relates Merle Moeckel, director of technical sales, Dean Foods, Amboy Specialty Products Division, West Chicago, IL. "The type of stabilizer system chosen will first depend on what type of process is used to make the sauce."
Different processes will contribute varying levels of stress. A frozen food manufacturer can simply do a batch kettle, 180°F process. Retorting requires temperatures around 230° to 250°F for 30 minutes, or longer. In aseptic processing, depending on the sauce, the cooking temperature will be in the 280° to 290°F range. In some systems, the sauce might go through equipment such as a swept-surface heat exchanger, where it gets physical abuse in addition to high temperature exposure.
The second important process consideration is shear. High shear can be encountered in the heat exchanger, especially with methods such as pasteurization or steam injection. Sauces also experience shear in pumping and filling operations. The shear varies with the type of pump used: a positive displacement pump will create less abuse than a centrifugal pump.
"Pumping can be a high-shear process, but it depends on the size of the pipes," says Mark Freeland, director of advanced hydrocolloids, Rhône-Poulenc Food Ingredients, Cranbury, NJ. "In production, many times you'll see a 3-inch pipe that is reduced down to an inch. You increase the shear forces at that point many fold, which can disrupt the stabilizer system. If you subject starch granules to that kind of shear, they will rupture."
Of hydrocolloids and handling
While high shear can destroy the starch granules and permanently change the viscosity of the finished product, it may only have a temporary effect on the gums used. Many hydrocolloid gums are shear-thinning, losing viscosity only under the influence of shear. Once the shear ceases, these gums return to their normal viscosity. This can provide advantages in heating and filling operations.
Improper mixing and failure to achieve complete hydration are common mistakes when adding stabilizers to sauce products. These mistakes can result in variable product viscosity and stability. For a cook-up starch, this means sufficient time to reach fall hydration. For a gum, it means proper incorporation techniques – that is, individualizing the particles before solubilization. Lumping is caused by fine particles touching each other. They can be separated by pre-mixing them with other dry ingredients such as sugar or spices.
"You can use high shear or create a slurry," notes Rhône-Poulenc's Freeland. "If you have oil in the product, you can make a slurry of the gum in the oil and separate the individual particles to prevent lumps. If a well-mixed oil slurry is slowly poured into the water phase with some agitation, most of the product will go in without any lumps."
With reduced- and no-fat products, you may not have oil, so you have to be a lot more aware of how you incorporate hydrocolloids into a food product. Agglomerated hydrocolloid particles need no special handling because they are designed to slowly hydrate during mixing. Agglomerated hydrocolloids also make sense in applications where heat exposure is minimal, such as dry sauce mixes. There also are other low-temperature viscosifiers.
"We've developed a cheese sauce and a gravy prototype using agglomerated hot water dispersible starches" says Augustine. "The intermediate pasting temperature starches – the ones that cook out at 110° to 130°F – give you flexibility for microwaving and for dairy-type products you don't want subjected to high temperatures. There are granular instant starches with intact granules like a cook-up starch but that have instant starch hydration. These give the convenience of instant hydration, but the stability, texture and appearance of a cook-up starch. They can then be agglomerated to give you that same capability with hot water."
If the sauce formulation contains fat, you may need an emulsification step and, to keep the fat from separating out, an emulsifier. Most methods of emulsification require high shear, which can affect a fully hydrated starch. One way to avoid this is to rearrange the process steps so homogenization occurs prior to gelatinization.
"From a processing standpoint, if you have an emulsion you want to stabilize, you want to have some hot viscosity to limit the amount of coalescence or flocculation during processing," Sanofi's Carr says. "It may be an oil-in-water emulsion you can stabilize with a hot viscous polymer like xanthan."
Addressing shelf-life issues
Another important function of a sauce stabilizer system is to maintain the desired finished product characteristics over the shelf life of the product. Both the time and temperature in storage influence the selection process. How pH can affect stabilizers holds true for storage as well as processing.
"The higher the processing temperature, the more emulsifiers you need to keep everything in place and to keep the fats and proteins from cracking out," notes Amboy's Moeckel. You may need more stabilizing salts and other emulsifiers as well as the modified starches."
In some cases, a viscosifier such as starch or xanthan will perform admirably as a stabilizer. However, a functional emulsifier often must be added to combat the tendency of oil droplets to coalesce and rise to the top of an aqueous product. Some stabilizers such as propylene glycol alginate have some surface activity, but sometimes emulsifiers such as mono- and diglycerides or stabilizing salts are necessary.
"Emulsifiers are a definite part of the system because they tie the products together," notes Larry Woodford, group manager of refrigerated products for Kraft Food Ingredients, Memphis, TN. "A cheese sauce would generally use some sort of phosphate, but you might add citrate to an aseptic product, sometimes even a sodium caseinate product. Part of the emulsification process is putting the ingredients together in the proper sequence. We recommend that the customers work with it until they feel comfortable with the equipment they have fitting into the process."
Many sauces are formulated to undergo frozen storage, so the stabilizer system must be freeze/thaw stable. A sauce made with an unmodified starch will exhibit poor texture and syneresis after one freeze/thaw cycle.
Substitution imparts freeze/thaw stability to a starch. Hydroxypropyl substitution improves water-holding ability and, consequently, freeze/thaw stability of the starch. Many starches are dual-modified: substituted for storage stability and crosslinked for process tolerance.
Although not a storage consideration in the traditional sense, many sauces need to be formulated to withstand foodservice conditions, especially extended holding times on a steam table. The stabilizer must be resistant to breakdown over long periods of relatively high – 160° to 200°F – temperatures. One of the most difficult problems is keeping the product from drying out, but there is only so much you can do from a formulation standpoint. "Stabilizers can bind moisture, but they can't stop evaporation," notes Gottneid.
"It's not uncommon for sauces and gravies in restaurants to sit for four hours and more," says Steve Miller, technical segment specialist, L.J. Minor, Solon, OH. "That's going to promote oil separation, so you really need to keep that emulsion from breaking down."
The last category to consider when formulating sauces is the finished product characteristics, including texture, flow properties, appearance and flavor. Keep in mind that the rheology needed for processing is not necessarily the same as required for consumption.
Different stabilizers can give different effects and these effects, in turn, are influenced by factors such as concentration and degree of solubilization. For example, when a starch is not fully hydrated, it appears opaque, has low viscosity and tastes starchy. Cooked properly, it turns translucent, has what some describe as a creamy texture, and provides a characteristic viscosity and bland flavor. Too high a level may give the appropriate viscosity for a specific application, but also will promote a starchy mouthfeel and even a characteristic but unwanted flavor.
"The majority of our products are based on waxy maize," says Staley's Augustine. "This has the highest viscosity and clarity with a given modification. But we use tapiocas for cream sauces: they have the blandest flavor, a little shorter texture."
Field corn or dent starches are slightly opaque with an even shorter texture. They're the ones that gel in the refrigerator. Potato starch has fairly high viscosity compared with some of the others because of its large starch granule. When modified, it would be appropriate for sauce products.
"Potato starch gives a little opacity," continues Augustine. "You don't see a lot of it in mainstream systems, but it is useful. Rice starch is also very bland. It's used a lot in baby foods, and some of it is used as a fat replacer to give some mouthfeel characteristics."
Gums, especially xanthan, are sometimes used as the primary viscosifier, but often they are used in combination with starch and other hydrocolloids to impart a certain quality or to modify the texture. For instance, one important quality for a sauce is cling. The exact quality can vary with the application, but in general the sauce should remain on whatever food it is being consumed with at the correct temperature.
"Barbecue sauce used while you're cooking ribs requires stability under hot conditions," advises Freeland. "If the barbecue gets up to 300°F, you want to make certain the sauce doesn't all run off into the charcoal briquettes."
Such a situation is different from that of a dipping sauce, which experiences ambient temperatures and must cling only for a matter of seconds, not 30 minutes. A simmering sauce is used in a skillet with meat and needs good cling on the pieces when served. Here, the temperature at the point of serving and the cling that you get at 120° to 140°F, a typical eating temperature, have to be taken into consideration.
Even emulsifiers provide textural and flavor effects.
"Cheese sauces can be all extremes, from a very emulsified sauce that is slick and smooth to those that are coarse and grainy having an open texture," observes KFI's Woodford. "The more open the texture, the more flavor release you'll have. Products like macaroni and cheese sauce may be designed with a coarser texture which is more like a homemade-style product. Products that are dippable tend to be highly emulsified, which ties up the flavor."
Formulating sauces combines art and science. This is true for functionality, as well as for taste and texture. Still, if you consider all aspects, designing a sauce that stands up to commercial applications can result in a five-star product.
Don't Stake on Stokes'
Among the many principles we learn in food science courses is one known as Stokes' Law:
v = 2/9 g r2((s - (f)/(
Where v = velocity of fat globule
g = gravitational force
r = fat globule radius
(s - (f = the difference in density between the fat and the aqueous phases
This table and the symbols it contains may not remain constant, depending on the word processing systems and fonts used. If you would like a copy faxed or mailed to you, please send an e-mail to [email protected], requesting the "1294AP Stokes' Law" table. Please include your name, address, fax number, etc.
In plain English, this means that in an emulsion, the smaller the globule, the slower it rises to the top in an action commonly known as "creaming out." The dairy industry uses this principle extensively for homogenization. But, according to researchers at Sanofi Bio-Industries Inc., Waukesha,WI, Stokes' Law may not hold true in all cases.
"Stokes' Law may be a good general rule for certain systems, but it may be different when you start looking at certain hydrocolloid stabilized emulsions," states Jim Carr, Ph.D., Sanofi's technical director. "We've done some research recently where we've looked at how much influence Stokes'Law has in sauce and dressing applications. We have seen, at least in studies using xanthan gum in model systems, that Stokes'Law doesn't have that much of an influence."
Normally you would expect the smaller droplets to rise slowly and the larger ones to rise more quickly. Using ultrasound and laser scattering techniques, the researchers noted that all sizes appeared to move at the same rate.
"There's something the physical chemists refer to as depletion flocculation," explains Carr. "It seems that xanthan-stabilized products are stabilized through a flocculation method. After a certain amount of time, all of the droplets move at the same rate. It appears that the way we think about emulsions and their stability will change as we continue to study these systems."
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