An Inside Job: Filling Basics & Beyond

Food historians claim the medieval predecessor to the modern piea delicacy somewhat morbidly called a coffynhad a crust that was effectively inedible.

Take a survey of the plate scraps the next time you serve pie and you may suspect the same of your own crust. Of course, thats meant as no slight against your pie-making prowess. Its just that, for some pie-eaters, the fillings the thing.

And they may have a pointand not just about pies, either. After all, whats a Fig Newton without its fig? A Twinkie without its fluffy vanilla creme? A Pop Tart without that mildly bemusing brown sugar-cinnamon jam? Its just dough, thats what. And the ineluctable appeal of what might lie within has intrigued us since four and twenty blackbirds were featured.

If bakery and bar fillings have quieted down since then, its been only in the literal sense. Metaphorically speaking, new developments in filling formulation are making a real buzz. In fact, theres never been a more exciting time to stuff stuff into cakes, crusts and cookie bars.

Musing on the 21st centurys new fillings, Michelle Huber, senior flavorist, Mastertaste, Inc., Teterboro, NJ, predicts a bright future. Theyre more flexible now, she says. I think manufacturers are doing more with them than they used to. Back when I started creating flavors, it was basically the same bake-stable fruit prep inside. It wasnt as exciting as it is now. Today we see a lot more functional fillings. We see caramels used as fillings. We see fillings that can set up on top of a bar. We see nutritional fillings. And that old-fashioned fruit prepstill the countrys favorite? Its not so old fashioned anymore. As Huber says, Theres a lot going on.

Critter control

Industry activity aside, the fundamentals behind bakery and bar fillings would still make sense to a housewife from the Fannie Farmer era. When Grandma made an apple pie, she probably hand-cut apples, says Scott Summers, director of technical services for ingredient and foodservice, Tree Top, Inc., Selah, WA. She used some kind of preservative, like lemon juice. And all she did was add pie seasonings and sugar, and then some starch so it would gel.

If that sounds familiar, its because the basic concepts remain the same, Summers continues. Todays manufacturers can make the fillings more viscous. You can raise or lower water activity. You can add more fruit. You can add less fruit, he says. But, whether its a toaster pastry or a Marie Callenders peach cobbler, it comes back to the fact that the only real twists are the different types of stuff we use to make the same old stuff.

So it should surprise no one that microbial management tops our list of concerns, as it always has. product designers have amassed an arsenal of toolsfrom packaging and thermal-kill steps to food-grade acids and frozen storagefor keeping intruders out, or making their stays less hospitable.

If you intend a product to survive on the shelfor desk, backpack or glove boxmicrobial reduction warrants heightened consideration, especially given the prominence of convenient, ready-to-go cereal bars in the marketplace. These bars get more shelf space every day, notes Huber.

It seems no matter where you goeven if its a Quik Martyouve got shelves upon shelves of bars. And if you go somewhere like a Trader Joes or Whole Foods, you see even more. The formulations and flavor types seem to be almost endless. According to a report from Mintel International, Chicago, Cereal Bars in the United States, the market grew 69%, measured at current prices between 2001 and 2006, raking in $1.4 billion in 2006 sales, Wal-Mart included.

Water, unbound

With shelf stability a key feature of these barsas well as of most filled cookie bars, toaster pastries and other popular snacksthe goal is clear. As Keith Parle, director of functional foods sales and strategic development, Kerry Sweet Ingredients, New Century, KS, says, Its all about water activity.

Namely, its all about lowering water activity (aw). When equilibrated between the surrounding matrix and the filling, the aw of a shelf-stable bar should fall between 0.70 and 0.75, according to the American Institute of Baking, Manhattan, KS. The aw of a filling alone might range from 0.50 to 0.70 for a shelf-stable toaster pastry to 0.70 to 0.90 for a frozen one. And, if the filling happens to be cold-processed, the absence of a kill step may necessitate even lower aw values.

Processors have traditionally tamped down aw via a number of means, including formulating with ingredients that dont have a lot of unbound water in the first place. For any type of bar system thats going to want some degree of shelf stability, Summers says, intermediate-moisture ingredients help get you there.

Indeed, raisins and other dried fruitsapples, apricots, figs, dates, plumshave appeared in fillings since Egyptian times. But dried fruits available today offer far more forms, flexibility and function than was accessible to the Pharaohs. Thomas J. Payne, industry specialist, California Raisin Marketing Board, Fresno, CA, touts raisin juice concentrate for its formulation benefits, particularly its ability to allow for the elimination of artificial preservatives and additives that sometimes appear in order to extend shelf life, he says.

Raisins contain naturally occurring organic acids that act as mold inhibitors. Raisin paste, produced by extruding 100% all-natural raisins through fine mesh screens, can also extend shelf life, Payne adds, while it lends humectancy, sweetness, a fat-like texture and flavor enhancement, as well. Raisin paste remains pliable and soft during storage, he says, and is extrudable and compatible with a variety of flavors and other ingredients. For example, it can easily be flavored with everything from lemon, cinnamon, peppermint, cherry and strawberry to licorice and jalapeño pepper. Though he suggests developers use it in applications where the presence of fruit particulates is needed, variable grinding conditions can yield paste textures ranging from coarse to smooth.

Sweet things

However, the real go-to ingredient for lowering aw is sugar. The first thing I always think about is water activity, and sweeteners are used to produce a low water activity, says Doris Dougherty, senior food scientist, Tate & Lyle, Decatur, IL. As sugar solids dissolve, they lock up the free water that microbes need to survive. The higher the solids, the more water the dissolved solids immobilize, and the more stable the filling. So, a fresh pie, which isnt formulated for long-term stability, may only need a sugar concentration of 35° to 60° Brix, while fillings in shelf-stable bars tend to be up around 75% to 82% solids, she says. Theyre quite high.

But not all sweeteners lower aw to the same degree. High-intensity sugar alternatives, such as aspartame, sucralose and acesulfame potassium, earn kudos for reducing calories, but their ability to capture free water is negligible. The shift toward alternative sweeteners will force formulators to look at a little higher solids level, taking out some of the water, or adding glycerin or sorbitol, Dougherty says. You still have to maintain low water activity.

Even traditional sweeteners show variable performance in lowering aw, which is a function of the sweeteners comparative colligative properties. That means the smaller the sugar, the lower the water activity, Dougherty explains. But this is only true to the extent that the sweetener is dissolved, she stresses. The critical thing about that statement is that sometimes we add these sweeteners with the expectation that they are going to lower the water activity, yet we may not get the impact that we expect because it isnt fully dissolving.

So, for example, dextrose is limited by its degree of solubility, Dougherty says. Crystalline fructose, on the other hand, will give good water activity control. Its a monosaccharide, so thats good, and its also highly soluble. High-fructose corn syrup (HFCS) is another reliable tool for enhancing sweetness and lowering aw, she adds, because youre adding a very high percentage of monosaccharides. Whats more, HFCS gives a very short texture, because youre not adding the highers compared to corn syrups.

Highersoligosaccharides with a maltodextrintype saccharide distributioncan yield a stringy, oozy filling. So, a corn syrup that has those highers in it would give a longer filling texture than a high-fructose corn syrup, Dougherty says. Whether thats an advantage depends on the product, but in a handheld bar meant to be eaten without leaving any fingers sticky, its probably not. Instead, she suggests using crystalline fructose or dextrose. Then youre not adding those highers, and you can control the texture.

Dextroses poor solubility poses yet another challenge this time to texture. Because of its limited ability to dissolve, it can create an unwanted grittiness. Thus, of the total sweetener solids, we generally say, as a rule of thumb, that you dont want to use more than 30% to 35% dextrose in a filling, because it can crystallize out, Dougherty cautions. She also emphasizes that you have to look at your entire sweetener system to make sure youre not getting too much dextrose from corn syrup and other places where you may not initially think about dextrose coming from.

But the truth is, packing too much of any sweetener into a filling can encourage crystallization. Products like these contain so much sugar, says Mar Nieto, Ph.D., director of technical services, TIC Gums, Inc., Belcamp, MD, and we know that sugar crystallizes out beyond 65%. As one solution, he says, what we can do is add gum arabic as a functional ingredient to prevent sugar crystallization. Its larger size relative to that of sugar interferes with the arrangement of the sweetener molecules, providing a physical barrier, as he calls it, that puts the brakes on crystallization.

Mass migrations

Where hydrocolloids, like gum arabic, and starches come into their own is in controlling the moisture migration dilemma in filled bars and baked goods. Consider the case of a toaster pastry. Its crisp, cracker-like shell surrounds a moist, sticky jam. That scenario represents a moisture differential that essentially guarantees the migration of water from the jam into the shell (or vice versa, if the crust happens to have higher moisture than the filling).

While this gradient sometimes works in our favoras in fig bars, whose soft texture is a happy corollary to moisture diffusing out of the filling and into the cookie if you have one section of the bar thats very thirsty for moisture, then it will tend to suck moisture out of other parts of the bar, and you can end up with issues like a caramel filling thats really soft and runny and a base thats like an adobe brick, notes Parle.

The question then becomes how to hold that moisture in place. Dried fruit powders offer a low-tech substrate to scavenge water in the system, Summers says. Basically, they are natural starches. They arent forming bonds or crosslinking, but they are binding water. And thats critical to the stability of all these fillings.

For a finer-tuned effect on moisture control, hydrocolloids and starches help with adjusting the viscosity or the gelling of the aqueous phase, says Andrea Peck, food scientist, Cargill Texturizing Solutions, Minneapolis. They help to slow the moisture movement.

Finding the right starch and hydrocolloid system for a filling involves a complex set of considerations, not the least of which is making sense of the many starches and hydrocolloids to choose from. Nature makes things complicated for us, because it provides so many types of gums that you can use, Nieto says. Some of them are freeze/thaw stable; some of them are not. Some of them are not stable at low pH, and some of them work better there.

Ultimately, says Bill Karpen, a senior technical specialist in Cargills Chicago offi ce, we arrive at the best choice by knowing the characteristics of the stabilizers selected and the environment in which theyre being used.

In particular, Peck advises paying close attention to that filling. Will it be bake stable or not? she asks. What is the acidity of the system? Then, by looking at the soluble solids and target texturefirm gel vs. smooth paste; viscous vs. thin; smooth and shiny vs. grainy and pulpy with a more fruit-like textureit will help to identify the right components to obtain the desired result.

Its a principle best illustrated through example. So, taking on the issue of acidity, Karpen notes starches and hydrocolloids generally tolerate a pH range of 3.1 to 3.5. This is a range that most fruit fillings rest comfortably in; however, a very tart filling might go even lower.

Peck adds, Most hydrocolloids, highly cross-linked modified starches and xanthan gums are typically quite good under such conditions. Carrageenans, however, are a notable exception.

In a key lime filling with a pH of 2.8, for example, even a carrageenan that would normally set will not work, Nieto says. His solution under these circumstances would be to pair xanthan with konjac to give you the best set.

Running hot and cold

Moving to the question of bake stability, Peck notes the baking of fillings may lead to boil-out, or spread of the filling during times of exposure to high temperatures. Spread may actually be an asset, ensuring a thorough fill of the matrix. But boil-out almost always creates messy headaches during production, slicing or packaging operations.

Even high-solids fillings can suffer its consequences because, as Nieto points out, sugar melts and can exacerbate boil-out, too. So, you still need to have something that will hold that water during baking to prevent the liquid from seeping out of the dough, he says.

Pectins, as it happens, provide just the right something. They are a good place to start when it comes to bake stability, Peck says, singling out high-methoxy (HM) pectins for their ability to impart a strong, bake-stable gel when used at low pH and high solidsroughly below a pH 3.5 and greater than 60% solids, respectively.

But, if your filling does not meet these requirements, low-methoxy conventional, or LMC, pectins and alginates will give the developer more flexibility, provided there is sufficient calcium available to help form a gel, she says. Further, combinations of pectin-alginate blends with other gums or starches will improve the range of textures and properties.

In some cases, we want a fillings texture to evolve as the product bakes. Depending on your process, Peck notes, you may need a thin texture to inject or deposit into cakes or onto bars. So, for instance, agars are typically used in icings for their process tolerancethey can be heated above their gel-setting points to pump through the lines, but set at lower temperatures.

Additionally, in the case of a pectin and locust bean gum combination for variable textures during processing, the pectin sets on cooling, while locust bean gum hydrates and starts to thicken at between 150° and 180°F, Nieto says. So, initially, its not so thick that the product cant be pumped, yet during baking it will thicken.

In cold-processed fillingsespecially those with high levels of sugar solidsinstant or pre-gelatinzed starches, alginates or a combination thereof manage moisture best. A pre-gelatinized or instant starch needs no cooking to initiate swelling, Peck explains.

Using the latter, the granules stay intact, which may result in a smoother texture. She suggests starting with a coarse particle size or agglomerated instant starch to ease incorporation and avoid lumps, and adds that proper agitation is essential to make sure that theyre effectively incorporated.

As for freeze/thaw stability, several hydrocolloid and starch combinations provide protection on that front. Starch manufacturers generally chemically modify starches in two ways: crosslinking and substitution, notes Peck. Crosslinking strengthens the granule by randomly welding various starch chains together, therefore increasing the resistance to acid and shear. Substitution, on the other hand, is the addition of functional groups to increase the clarity, ease of cooking and moisture retention of the starch, she explains. Its these substituted starches that do the trick when freeze/thaw resistance is needed.

For extended frozen storage, Peck recommends combinations of substituted starch and xanthan for greater stability. In fact, xanthan and other cold-water-soluble gums consistently hold up well under frozen conditions. So long as theyre compatible with the surrounding pH, Nieto says, all the gums that are soluble in cold water, like xanthan, guar gum, konjac and CMC, will not be affected by freezing.

The rule of thumb is that when a gum freezes, it reverses back to its original properties, he explains. So, traditional agar, which requires near-boiling temperatures to dissolve, doesnt weather frozen storage well. When you freeze it, he continues, water is removed from the molecule and it reverses back to being insoluble. Similarly, locust bean gum is only sparingly soluble in cold water; you hydrate it by heating, but when you freeze it, the water is squeezed out and it reverses. It may not revert fully to insolubility, but it loses its water-binding property until its reheated.

A clean fill of health

And thats something you dont want to lose. Yet, if Nietos experience is any guide, we may start seeing gums and hydrocolloids showing up in fillings for more than just their ability to bind water. Now, customers are trying to add health benefits to the consumption of these products, he says, and they want us to help add fiber. Conveniently enough, hydrocolloids such as carrageenan, pectin, gum arabic, guar gum, locust bean gum, acacia gum and xanthan gum are all sources of soluble dietary fiber, In fact, he says, were fortifying a snack bar filling with a fiber blend containing gum arabic, inulin and pectin right now. The advantage of inulin and gum arabic, he points out, is their viscosity doesnt limit their use. So, you can actually load your snack bar with gum arabic and inulin and not get thickening that turns it into a brick. By contrast, even at a level of 1% to 2%, xanthan gum or guar gum would be too thick.

Using the arabic, inulin and pectin blend, Nieto and colleagues have squeezed as many as 5 grams of fiber into a standard-sized bar. But 2.0 to 3.5 grams is the normal fiber level that you would want to see on the label, he says. Just enough for that fiber claim.

Another advantage of the blend, Nieto continues, is that inulin brings a prebiotic boost that consumers increasingly recognize for its ability to encourage healthful probiotic bacteria. But its not the only prebiotic in the mix. Gum arabic, pectin, guar gummost of the gums are very prebiotic, he says. The exceptions are nonfermentable hydrocolloids like xanthan and carboxymethylcellulose, or CMC. As he points out, CMC is still cellulose- based and its very indigestible to bacteria in the gut. So, it really depends on what gum youre using.

Additionally, Dougherty notes, theres always the opportunity to add our Promitor soluble corn fiber to fillings to reduce the sugars and provide fiber. A proven prebiotic, the Tate & Lyle product is soluble corn fiber derived from the starch portion of the grain, that provides about 70% fiber on a dry-solids basis. It can be labeled as soluble corn fiber or corn syrup, she says, and while it contributes little of corn syrups sweetness, it does replace its bulk and exhibits similar functional performance and properties. That means reliable process and acid stability, clarity in fillings and low viscosity. Yet, at only 2 kcal per gram, and with a low glycemic impact, it shoulders none of the nutritional burdens that have dogged corn syrups and other conventional sweeteners lately.

The trend toward functional fillings has even hit Hubers lab. Were seeing a lot more nutritional fillings, she says, and the development of these has kept her team busy customizing their flavors. With omega- 3-fortified fillings becoming more popular, thats one of those things that we get asked to try and mask all the time, she says. Most of the unflavored bases that we see are not very pleasant. There are different qualities and different sources of omega-3s, but most of the ones we are asked to work on have the characteristic fishy profile. Brown flavors are dependable choices to go head-to-head with the ingredients, she says, and Ive seen them work well in fat-based fillings, too. Fat-based fillings with either coffee flavors or dark chocolate flavors tend to be the best.

On the lighter side, shes been getting requests to flavor fillings pumped up with extracts and botanicals. As for which flavors best mask their medicinal notes, it depends on the botanical, she says. Some of the botanicals that were working with actually lend themselves to exotic flavors, like a lychee flavorsomething thats slightly floral. However, while an exotic lychee profile might be something that we do here and everybody thinks is great, sometimes customers worry about how acceptable some of the exotic flavors will be for their consumers. In other words, you often cant beat good-old fruit, typically, a natural berry flavor, she says.

Fantasy fruits

Nevertheless, Huber concedes, were always getting the new fruit of the day or a new indulgent flavor that needs to be developed. Customers are moving more toward things like goji berries, which, as anybody whos ever had goji juice can tell you, isnt very pleasant. So, at times we end up creating more of a fantasy-type flavor than a flavor typical of the fruit.

Even so, the fantasy is fast becoming reality. According to Summers, the reality is that any fruit is a vehicle for any one of these bar fillings. Apple, cherry, peach, berry, banana. Those are the classics, he admits. But the up-and-coming fruitsthe ones that people are excited aboutare the pomegranates and exotic things.

Fortunately, the raw materials are no longer so exotic themselves. Ill bet you nickels to dollars that goji berry is available in a purée, Summers says. Individually quick frozen might be a stretch, but thats probably not your first choice anyway. Itll be some kind of preliminarily processed fruit base. Itll be a goji berry concentrate; itll be a pomegranate puréeitll be some form of partially processed fruit that is new and exciting and everybody is all wound up about it. Then the job will be to take whatever form its available in, be it purée or concentrate, and work it into a formulation system.

Which is where the economics step in. The rules are pretty simple, according to Summers. You need to establish the budgetary constraints up front. And that, in turn, is driven by what the consumer is willing to pay. So, if youve found a source for goji berry concentrate, then you have the option of using goji berry as your primary or secondary fruitand as a sweetener, as well, he explains. So, all of a sudden youve got goji concentrate at 70° Brix as a natural sweetener and youre getting the goji-berry primary fruit profile.

But when this beta version winds up costing $35 per bar, then the question becomes, how much of that 70° Brix goji berry concentrate do you want to use? he asks. All of a sudden it becomes a goji berry WONF bar, where weve put some goji berry in at 2% and a little bit of natural flavor, and were really selling white grape- or pear-juice concentrate.

The message has to get through loud and clear to the consumer, though: This bar has goji berries. Thats because it all comes back to points of identity, Summers says. Its visual perception. So, the amount of fruit is less relevant than the visual perception of fruit. And there are lots of ways to make people perceive that there are little pieces of fruit in there. Take the addition of seeds to a filling, for example. Color counts, too. Were still coloring and flavoring apple bits, and manufacturers are still using colored and flavored pieces to define other fruits.

Sweet, savory and more

You dont even have to stick with fruit. Huber has seen what she calls a slight shiftbut its slowertoward savory bars.

Thus, we have the sweet-salty profiles that the mainstream guys picked up on last year, Parle says. He cites figures showing that, in 2007, sales of Nature Valleys Sweet & Salty Nut Barsthe fastest-growing bar in the granola categoryrose 47% over the prior year, clearing $7 million in sales for the four weeks ending June 17, 2007, alone.

But sweet-salty isnt the only story. Were also being asked to do more spice concepts, Huber says, where the filling would be peppery or Tabasco-flavoredsomething like that. It hasnt been wide-reaching, but we are being asked for those things.

More immediately accessible to public palates are those classic brown notes. Were seeing a lot more sweet browns now, Huber says, and their prospects are aided by the fact that todays generation of caramel fillings represent a marked improvement on their predecessors. And thats no mean feat, either, as making caramels is an art, she says. Having spent time working with Kerrys caramel and variegate group, she has observed that, over the years, theyve have gotten it to the point where its not just caramel anymore. It can be used as a filling. It can be used as a binder. It can be used as an extrudable caramel to set up on top of the bar. Theyre more versatile than they used to be.

Bringing the inside out

Indeed, Parle says, were developing caramels that would allow bar makers to go to market with a shelf-stable caramel and not have to doubly enrobe the bar. Classic layerable caramels, he says, flow and are intended to be enrobed so that the chocolate coating on the outside is supporting the caramel on the bar. What sets apart new extrudable caramels is that, if a manufacturer wanted to, they could just bottom-enrobe the bar with caramel, and the caramel on the bar is actually strong enough on its own to set up and stay on the bar. Its as if weve taken the filling from the inside and spread it on the outside.

Refining the technology has presented its challenges, one of which, Parle says, is the task of designing a caramel thats strong enough to set up and yet allows something like peanutsbut not the foil packageto stick to it. Not surprisingly, the solution has involved formulating with a proprietary blend of hydrocolloids that render the caramel soft to the tooth, like a traditional caramel filling, yet sturdy enough to hold its place on the bar. As an added bonus, the new caramel formulations eliminate the problem of bridging, which occurs when a layerable caramel, as its deposited, bridges the gap between two separate bars on a depositing line. And then, he says, you end up with one big bar joined by a sticky strand of caramel. And thats not good.

Kerry has applied the same extrusion technology to producing extrudable fruit leathers that can hold their own as inside-out fillings on bars. As with the caramels, these non-cold-flowing fruit layers extrude across the top or bottom of a bar without sticking to fingers or wrappers, obviating the need for a protective enrobing layer.

There are specific hydrocolloids and gelling systems that are used to create that type of non-cold-flow texture, if thats whats needed, Parle says. Some customers want it actually to look more like a preserve or a jam, so when you bite into it, it actually does flow. And those tend to be formulated with different hydrocolloids. As for the range of textures possible, he says, think of date paste and think of strawberry jam and anything in between. Frankly, we can go even thinner than jam. Such a layer still wont make your hands messy, he insists, but it will ooze. It makes the bar look like its rich: Ooh, I want to eat that!

Concentrates and drum- or freeze-dried fruits are common base ingredients for these extrudable fruits, depending on what the ultimate goal is, Parle says. With apple still the most economical starting point, typically, theyre formulated with apple and then theyre naturally flavored to be strawberry, peach or you-name-it. And, he adds, if you formulate strategically, you can claim a full serving of fruit in a single bar. People havent quite gone that far, he notes, as the kicker is obviously the cost. While that may be so, customers, he says are still using them to claim contains real fruit. And, in any event, with a Kerry Americas survey finding that the No. 1 thing consumers want in a bar is real fruit ingredients, being able to deliver as much as 20 grams of fruit in a 50-gram baras the extrudable layers allowis a net plus for all.

Consumers who are looking for more protein and less fat can turn to yet another version of these extrudable layers: a protein-fortified, fat-free creme. It effectively can replace the requirement to have a compound coating on a product, Parle says. And although we call it a creme layer, theres no fat in it. Credit the total dairy protein that he says is the main ingredient. It contains 22% protein, and virtually no fat. Its nothing like a compound coating where you might have 30% to 35% fat. He suggests using the products as you would an icing on top of a bar. Theyre a light, creamy color, although weve made up lemon and strawberry and chocolate and peanut-butter flavored versions. But the one thats out there most prevalently is still a vanilla toping.

Perhaps theres a lesson in there somewherespecifically, that some things, including our favorite filling flavors, may never stray far from the norm. That doesnt mean we wont keep trying to shake things up. A lot has been done, Huber says of filling formulation. Its a matter of how much still can be done. And people have to look for that next best thing. So, theres a lot of experimentation that may not necessarily get out to the marketplace, but were definitely seeing the requests come through.

Kimberly J. Decker, a California-based technical writer, has a B.S. in Consumer Food Science with a minor in English from the University of California, Davis. She lives in the San Francisco Bay area, where she enjoys eating and writing about food. You can reach her at [email protected].