Yogurt Making

Yogurt is a tangy, nutritionally excellent dairy product that can be made at home. The milk used contains a higher concentration of solids than normal milk. By increasing the solids content of the milk, a firm, rather than soft, end product results. Addition of nonfat dry milk (NFDM) is the easiest at-home method for doing this. Yogurt is made by inoculating certain bacteria (starter culture), usually Streptococcus thermophilus and Lactobacillus bulgaricus, into milk. After inoculation, the milk is incubated at approximately 110°F ± 5°F until firm; the milk is coagulated by bacteriaproduced lactic acid. Making yogurt at home is fun and less expensive than buying it. It can be made with ordinary kitchen utensils. The materials and directions necessary for making yogurt follow.

Starter Culture Dry cultures for making yogurt can be purchased in some health food stores, but they are usually expensive. Dry cultures also may be purchased directly from a manufacturer such as: Chr. Hansen's Laboratory, Inc., 9015 West Maple Street, Milwaukee, Wisconsin 53214. The easiest and least expensive way of obtaining a starter culture is to purchase plain yogurt at a grocery store. It should be plain--no fruit added. Fruit may contribute undesirable yeasts and bacteria to the yogurt, making it a poor starter culture. You must use a brand of plain yogurt whose label indicates that the product contains a live culture; some brands of plain yogurt do not contain a live culture because the yogurt has been pasteurized. To maintain a culture, save a small portion of yogurt (1 c is enough for a 1-gal batch) to use as a starter culture for the next batch. Be sure to refrigerate the starter culture in a clean, air-tight container. From time-to-time a culture may become contaminated, and a new culture is needed. By using a new culture, the original flavor and a minimal coagulation time are retained.

Temperature Accurate temperature control helps assure rapid coagulation and a good-tasting yogurt. A thermometer that measures temperature in the range of 90°F to 120°F should be adequate. A good stainless steel thermometer (Model 2292) is available from: Weston Instruments, Inc., 614 Frelinghuysen Avenue, Newark, New Jersey 07114. A glass thermometer can be used, but may break easily. Thermometers are not needed with special yogurt-making equipment.

Ingredients

Yogurt can be made by using only nonfat dry milk (NFDM) and water, or by adding NFDM to skim milk, 2% milk, or regular milk. Nonfat dry milk is commonly available in two forms, instant and regular. Ideally, the milk powder should be weighed to obtain the desired solids content (15 percent on a weight basis). Because weighing might not be possible in all home kitchens, measurements both by weight and volume are provided in the following recipes (Table I). For each recipe, the quantity of ingredients necessary for making either 1 qt or 1 gal of yogurt is given. Table I - Yogurt Recipes Recipe 1 Liquid Ingredient

Dry Ingredient NFDM* By weight

By volume Instant

Regular

1 gal water +

22.2 oz =

8 1/3 c

or 4 3/4 c

1 qt water +

5.6 oz =

2c

or 1 1/4 c

1 gal skim milk +

10.4 oz =

4c

or 2 1/4 c

1 qt skim milk =

2.6 oz =

1c

or 1/2 c

1 gal 2% milk +

7.2 oz =

2 3/4 c

or 1 1/2 c

1 qt 2% milk =

1.8 oz =

3/4 c

or 1/3 c

1 gal regular milk + 4.8 oz =

1 3/4 c

or 1 c

1 qt regular milk +

1/2 c

or 1/4 c

Recipe 2

Recipe 3

Recipe 4 1.2 oz =

*NFDM = Nonfat dry milk gal = gallon oz = ounce c = cup

Method for making yogurt 1. Mix the appropriate quantities of liquid and dry ingredients given in Table I. 2. Heat this milk in a saucepan or double boiler to boiling and cool immediately to 110°F. Discard any "skin" that may have formed on the milk. Sugar may be added to the milk before boiling, if desired. Heating the milk to boiling kills any undesirable bacteria that might be pre-sent and also changes the properties of the milk protein so that it gives the yogurt a firmer body and texture.

3. To 1 gal of milk, add 1 cup of warm 110°F starter culture. Mix well but gently. Do not incorporate too much air. If too much air is mixed in, the starter culture will grow slowly. 4. Sanitize yogurt containers by rinsing with boiling water. 5. Pour milk into clean container(s) and cover with lid. If fruit is to be added to the yogurt, put in the bottom of the cup before adding the inoculated milk. The fruit should be at a temperature of 110°F. (Omit fruit from a small portion of the recipe and save it to use as a starter culture in the next batch.) Incubate filled containers at 110°F. Do not stir the yogurt during this period. There are several ways to control temperature during incubation: a. Special yogurt-making equipment allows for careful temperature control without a thermometer and reduces the chances of failure. b. Yogurt containers can be kept warm in a gas oven with pilot light and electric bulb, or an electric oven with light bulb of sufficient wattage (approximately 100 watts). c. A Styrofoam box with light bulb may be used as an incubator. d. Another good way to control temperature is to place yogurt containers into pans of 110°F water in an oven or an electric frying pan. Set oven temperature at lowest point to maintain water temperature at 110°F. e. Wide-mouth thermos bottles, heating pads, and sunny windows also have been used. Regardless of the method of temperature control used, determine ahead of time that the proper temperature can be maintained. To do this, place water or a container of water in the incubator and monitor its temperature with a thermometer. 6. Maintain 110°F temperature until the milk coagulates with a firm custard-like consistency (3-6 hrs). Check by gently tilting cup. Then refrigerate. It will keep for two to three weeks in the refrigerator. 7. Enjoy!

Trouble Shooting 1. Problem: Yogurt does not have a custard-like body but rather is soft and not smoothly solidified. Causes: a. Addition of starter culture to the milk before it has cooled down may kill the culture and prevent coagulation. Solution: Wait until the milk cools down to 110°F before noculating. b. Both high and low incubation temperatures slow down culture growth and increase the amount of time necessary for coagulation. Solution: Use a thermometer to control temperature.

c. Extended storage of the starter culture reduces the number of live bacteria in the culture. Solution: Use more starter culture in the recipe or obtain a new culture. d. Contamination of the culture with undesirable bacteria. Solution: Get a new culture. Also clean and sanitize yogurt containers each time yogurt is made. e. Omitted or added an insufficient amount of nonfat dry milk to the milk. Solution: Accurately measure or weigh the nonfat dry milk. f. Over-agitation before incubation may slow down starter activity. Solution: Combine starter culture and milk by mixing gently. 2. Problem: Yogurt tastes bad. Causes: a. Starter culture is contaminated. Solution: Obtain new culture. b. Yogurt has over-set or incubated too long. Solution: Refrigerate yogurt immediately after a firm coagulum has formed. c. Overheating of the milk causes an off-flavor. Solution: Do not overheat the milk. 3. Problem: Whey collects on the surface of the yogurt. Causes: a. Yogurt was over-set or incubated too long. Solution: Refrigerate yogurt immediately after a firm coagulum has formed. b. Yogurt was bumped, moved or stirred during incubation. Solution: Place yogurt in a quiet location where it will not be disturbed. *This NebGuide was originally prepared by Stan Wallen, former Extension Food Scientist.

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Page 1 HOW PROCESSING AFFECTS STARCH SELECTION FOR YOGURT by Jeffrey W. Foss National Starch and Chemical Company, Bridgewater, NJ.

Starch is an important ingredient in today's popular Swiss and French style yogurts,  which together define the growing stirred yogurt market segment. Stirred yogurts differ from the traditional fruit­on­the­bottom (FOB) products in that they come with fruit and flavor  pre­mixed into the yogurt. Starch is typically used in these yogurts to impart viscosity, improve  mouthfeel, extend milk solids, and prevent wheying off, the separation of a clear liquid (whey) from  the yogurt mass in the cup. When used alone or as part of a stabilizer blend, starch is the  preferred thickening agent in yogurt due to its creamy texture, processing ease, and low cost when compared with other hydrocolloids. Yogurt processing conditions vary among dairy manufacturers, and this affects the type of starch that will work best for a given product  target. This article describes how processing variables affect the starch, and will enable the  product developer to match the proper starch to the specific conditions to meet the targeted  texture. First, a few basics on yogurt and its manufacture Though an important food staple to the Middle Eastern people for more than 5000 years,  yogurt has only recently become popular in the United States, largely due to an increased  appreciation of healthy eating. In 1998, yogurt sales topped 1.7 billion dollars, up 3% from 1997  (Source: Information Resources, Inc.) Consumption today is now about 5.2 pounds per capita,  more than triple of what it was 25 years ago, and can be expected to increase as yogurts containing beneficial probiotic cultures are being increasingly touted for colonic health. Much of the market's growth can also be attributed to manufacturers' ability to keep up with the  evolution in consumer preferences. A variety of new textures, colors, and packaging schemes have  been introduced to target the exploding "kids" segment of the stirred yogurt category. Exotic  colors (including swirls), mild flavors, and catchy advertising themes on the containers have  made

eating yogurt more appealing to the younger generation. Moms also appreciate the new  multi­ pack, smaller containers that make it easier than ever to get this great lunch supplement  into their childrens' lunch boxes. Yogurts with trendy dessert­like flavors and higher fat and sugar  contents are also being introduced to satisfy a recent shift in consumer preference towards  indulgence. Although "healthy eating" and "indulgence" appear at odds, today's yogurt products are successfully bridging this apparent paradox by enabling consumers to feel they are  partaking of a healthy dessert, and therefore getting the best of both worlds. This push towards more  creamy, pudding­like textures has also triggered a greater demand for nondairy stabilizers, such as starches, which are required to achieve these textures. This preference shift is at the  expense of the FOB segment whose products are now considered by some as somewhat passé along  side the more rich, creamy, and often colorful stirred types. Current market indicators show that  stirred yogurts have about a 70% share compared with the FOB types. FOB Yogurts The main difference between FOB and stirred yogurts is textural, with the former being  very firm and cuttable, and the latter soft and slightly flowable. This difference is primarily  due to changes in the yogurts' final processing steps. With FOB style yogurts, the pasteurized  milk slurry is inoculated with cultures, and then pumped warm directly into its final consumer Page 2 package (with or without fruit on the bottom,) where it is fermented. The pH drops during fermentation and causes the milk's casein protein to coagulate and form a gel. After  cooling, this cup­set yogurt is firm and very cuttable, due to the gelled casein in the system. This cup­ set manufacturing method is considered the traditional way of yogurt making, with its roots  in ancient Mesopotamia when storing goats' milk in the warm climate often resulted in the formation of a curd. Due to the strong set of these yogurts, supplemental hydrocolloids or

stabilizers are not often used. Without a stabilizer present to bind water though, a heavy  wheying off usually occurs by the time the product reaches the consumer, having been accelerated  by the jostling the product receives during distribution. Wheying off is considered a serious  defect; not only is the presence of free whey on the yogurt's surface visually unappealing, but many consumers incorrectly view the wheying off as a sign of spoilage. In turn, some  consumers will pour off any free whey before eating the yogurt, especially if it is extensive, as in the case  of many non­stabilized, cup­set yogurts. Incidently, this whey contains substantial protein,  and is therefore nutritious and should be stirred back into the yogurt mass. If stabilizers are used  in cup­ set yogurts, they are usually added only at very low levels (typically less than 1%) lest the texture becomes too firm. Also characteristic of cup­set yogurts is a somewhat chunky,  grainy appearance after the yogurt is stirred. Stirred Yogurts In contrast, stirred yogurts are smoother, and despite being less firm, more full­bodied  after stirring. To make a Swiss style yogurt, the pasteurized milk slurry is pumped into a large  vat and fermented to the desired pH. After the fermentation is complete, the yogurt is cooled,  blended with fruits and/or flavors, and packaged for sale. The pumping action disrupts the milk  protein gel network, and without the use of an added stabilizer, would result in only a slightly  thickened fluid product with little set. Therefore, nondairy stabilizer blends, such as modified food  starch and gelatin, are normally used to boost the viscosity to a pudding­like consistency, and  deliver the slight set that is characteristic of these yogurts. The starch in the blend also absorbs  the water in the yogurt system and prevents the whey separation typically found in the FOB  yogurts.

Texture Measurement Graphs depicting product quality data and rheological measurements are used as a means  of presenting product differences. These graphs, or icons, can serve as textural "fingerprints"  for yogurts. The larger the spoke for each axis of the icon, the greater that attribute is  expressed in the product. The measurement of several rheological attributes offers a more complete description of the yogurts' texture than single­point viscosity measurements (e.g.  Brookfield, Bostwick, etc.) and/or subjective sensory terminology alone. Rheological graphs  comparing the texture of typical FOB and Swiss style yogurts are seen in Figure 1. Page 3 Data for the firmness, elasticity, viscosity, and breakdown axes of these icons were  obtained using a RFS2 Controlled Strain Fluids Rheometer, and are presented with whey  separation and graininess data. Firmness refers to the yogurts' stiffness; elasticity refers to the ability of  the yogurts to recover after deformation; viscosity refers to resistance to flow under shear;  and breakdown refers to the size of deformation required to cause flow. Whey separation was measured after the products were disturbed to simulate distribution; and the degree of  graininess was judged by a trained panel. These icons clearly display the textural differences in each product as described above. Note that while the overall viscosity values are similar for  each product, the high initial firmness and breakdown values for the FOB yogurt reveal a rigid,  highly cuttable texture relative to the Swiss style product, whose low firmness, low breakdown,  and high elasticity values indicate a somewhat less cuttable, pudding­like texture. The lower  whey separation in the Swiss yogurt also demonstrates the stabilizer's ability to hold water. Since starch/stabilizer blends are required for stirred yogurts, this article focuses on the  best use of starches in such products. Much of this information also applies to starches for cup­set

yogurts. A wide range of starches is available, and a proper understanding of their role  and functionality is needed to choose the correct starch for the yogurt system. Page 4 Starch Modification and Processability As starch is heated, its granules lose their crystalline micellular structure, imbibe water  and swell to many times their original size. This swelling results in increased viscosity in the  cooked mixture. Uncooked waxy maize starch granules measure 5 to 20 microns in diameter,  whereas fully swollen granules can be 75 microns or more. A well­cooked starch typically has  about 80% or more of its granules in a fully swollen state. To understand the response of starches to heating, holding, and cooling cycles, the starch industry uses pasting rheometers, like the Brabender Visco/Amylo/Graph. A starch  suspension is heated in the unit's revolving cup through a preset temperature profile and forms a paste.  Torque exerted on a spindle positioned in the starch suspension is continuously recorded on a  chart to produce a pasting curve. This data is helpful in determining a starch's gelatinization  onset temperature, rate of thickening, peak viscosity, breakdown, and thickening (set­back)  during heating and cooling. Starch manufacturers often use this information for quality control measurements, as well as to predict starch performance in a food application. Swollen (cooked) starch is sensitive to extended hold times at high temperatures and/or excessive shear during processing. Heat and shear can cause swollen starch granules to  rupture and lose viscosity, unless the starch has been modified to withstand such conditions. A  food starch is considered modified when it has been treated to affect its performance in  applications. The two modification methods most commonly used in food starches are cross­linking  and mono

substitution, or stabilization. For the high temperature, high shear yogurt manufacturing  process, starches that have been cross­linked are generally required. The cross­linking treatment strengthens the starch granule and prevents it from over­cooking or over­shearing during  harsh processing. The more cross­linked a starch is, the more it is said to be inhibited, and the  greater its resistance to processing. In figure 2, there is a comparison of a Brabender viscosity  profile of a moderately cross­linked waxy maize starch to that of a non­cross­linked (native) waxy  maize starch under temperature conditions which simulate those experienced in yogurt  manufacturing. Figure 2 – Brabender/Viscosity Curves ­ Cross­linked Waxy vs. Native Waxy Page 5 The cross­linked starch maintains its viscosity, while the native version breaks down significantly. Translated into the finished yogurt, the cross­linked starch would give  higher body, while the native starch would produce a thin, unstable product. Because processing  temperatures and shear rates vary widely among dairy operations, it is important to choose a starch  with the optimal level of cross­linking. Stabilization, the other most common food starch modification, also improves starch performance in yogurt. Stabilizing groups added to the starch block the reassociation of  the amylose and amylopectin polymers within the granule, and maintain the starch's smooth  texture and viscosity stability. For a yogurt system, this would translate into textural stability, as  well as a minimization of curd shrinkage over time, which can also contribute to wheying off. In addition, certain types of starch stabilization treatments improve the mouthfeel and  creaminess of dairy products. For these reasons, highly stabilized starches are normally preferred in  yogurts. Stabilization, however, can also cause a starch to cook out easier, so a starch with a  combination

of cross­linking and stabilization is usually required in the high temperature, high shear  yogurt manufacturing process. In general, under processing conditions involving lower temperature, pressure and shear,  starches with a medium level of inhibition are recommended, whereas for processes with higher temperature and shear, highly inhibited starches are needed. It is important, however, to  look Page 6 closely at specific control points within the process since they can vary widely among  yogurt manufacturers. These variations can greatly affect starch functionality and influence the  type of starch to use. Typical Swiss Style Yogurt Formulation and Manufacturing Process A formulation for a typical Swiss­style, lowfat yogurt is given in Figure 3. Figure 3 ­ Swiss formula (1% Milkfat) Ingredients Percent weight Skim milk (Standardized to 1.2 percent milkfat) 89.65 Sugar 5.00 Non­fat dry milk 2.80 When protein concentrate (34 percent protein) 1.00 THERMTEX® starch (by National Starch and Chemical Company) 1.20 Gelatin (225 bloom) 0.35 Total 100.00 After the dry ingredients (dry milk powder, sugar, starch, whey protein concentrate, and  gelatin)

have been thoroughly mixed into the milk, the slurry goes through a pre­heating phase  which further dissolves the ingredients and helps in the achievement of the final pasteurization temperature. The pre­heating temperature of the slurry often depends upon the efficiency  of the plant's heat regeneration system, and can vary between 150 degrees F and 180 degrees F  (65­82 degrees C). After the pre­heat, the slurry (also referred to in the industry as the white  mass mix) is homogenized, normally between 500 and 2,500 psi (35­175 bar). The purpose of homogenization is to achieve mixtures (and subsequently yogurts) that are less likely to  separate, as well as to produce smoother, more glossy textures. This is accomplished by particle  size reduction of the ingredients in the mix, particularly the milk fat. Homogenization involves forcing a mix through a small orifice or passageway. As the passageway size is reduced  and the flow rate is maintained, pressure builds and particles break apart as they pass. This makes  the mix more "homogeneous." The higher the pressure, the greater the particle size reduction. Homogenization is often more effective when done twice, because low­particle­size fat  globules tend to agglomerate. A two­stage homogenizer is therefore often employed to break up  those agglomerates. Fat particle sizes of 5 microns or lower are normally achieved under  moderate homogenization pressures (1000/500 psi,) and adequately stabilize the milk fat in yogurt applications. After homogenization, the mix is pasteurized (typically with a plate heat  exchanger) to between 185 degrees F and 200 degrees F (85­93 degrees C) and held at this  temperature for 30 seconds to 5 minutes or more with holding tubes. This is referred to as HTST (High Temperature, Short Time) pasteurization. A plate heat exchanger (PHE) consists of a pack  of parallel stainless steel plates in which the product (milk slurry) and the hot media (steam  heated water) flow along the surface of alternate plates in adjacent streams. These plates are  corrugated

in a pattern to provide turbulence for maximum heat transfer efficiency, and thus achieve  a thorough cook of the slurry. PHEs are able to maintain the high pasteurization  temperatures required for yogurt manufacture even at very high flow rates (>2,000 gal/hr) (7571  liters/hr) and Page 7 their compact design requires minimal floor space, thereby maximizing throughput  capacity. Figure 4 illustrates the heat exchanger process through the plates. After pasteurization, the mix is cooled to a temperature between 105 degrees F and 110  degrees F (41­43 degrees C), and inoculated with live bacterial cultures. Cooling the mix to this temperature range is crucial to ensure the cultures' viability. The inoculated mix is then  incubated within this temperature range, enabling the cultures to ferment lactose (milk sugar) to  lactic acid. This in turn lowers the pH of the mix to the isoelectric point of the casein protein, which coagulates the milk causing it to set. The lactic acid development is also responsible for  the yogurt's characteristic tart flavor. Once the pH has dropped to about 4.5­4.6, the yogurt is  broken by tank agitation and pumped through another heat exchanger to rapidly cool it to  between 50 degrees F and 85 degrees F (10­30 degrees C). The yogurt is also often pumped through a  screen or smoothing valve to give a smoother texture before being mixed with fruit, and  packaged and refrigerated. Figure 5 illustrates the above process. Page 8 Figure 5. Processing and Starch Choice Although the process flow described above is the most common in the industry, other  variations are sometimes used. For example, some manufacturers homogenize the white mass mix  after pasteurization; some do not homogenize at all. Some do not preheat. Some manufacturers  batch­

pasteurize, for instance with a steam­jacketed kettle, employing LTLT (Low Temperature  Long Time) pasteurization. Process flow differences among manufacturers are often due to manufacturing volume, equipment and/or facility limitations, or necessary  accommodations for running other dairy products (which require the alternate flows) on the same production  lines. When considering a starch recommendation, process flows are evaluated case­by­case,  taking into account the sequence of pasteurization and homogenization, as well as the  temperatures and stresses involved. The two control points in the manufacturing process most critical to starch functionality  are the pre­heating and homogenization steps. The starch gelatinization(swelling onset)  temperature in sweetened milk is about 155 degree F (68 degrees C). Pre­heating the white mass mix to  180 degrees F (82 degrees C,) which is well above the starch's gelatinization temperature,  will begin Page 9 to swell the starch. The partly swollen starch is then vulnerable to the shear imparted  during homogenization, especially if the homogenization pressure is high (>2000 psi) (138 bars). Granules that are partly or fully swollen (in the order of 25­75 microns in diameter) are  fragile, and are significantly more prone to damage during homogenization. This shearing can  fragment the starch granule and significantly reduce its thickening capacity, resulting in a yogurt  with low body. This generally requires the manufacturer to use a greater­than­necessary amount of  starch or stabilizer blend in the formula to achieve the targeted viscosity. An even more dramatic  loss of viscosity would be evident if the homogenization followed pasteurization rather than  preceded it in the process flow. The starch granules, already fully swollen from the pasteurization

temperature, would be completely torn apart by the shear, and contribute even less  towards viscosity. So, while homogenization is an important step in yogurt manufacturing it can  be devastating to the starch if done at too high a temperature. On the other hand, pre­heating the mix to only 150 degrees F (65 degrees C) or lower will  not swell the starch, and the unswollen starch granules, because of their small size and high micellular strength, will generally withstand the homogenization process, even if the  pressure is high. The intact starch granules will then swell with minimal fracturing during the  pasteurization heating step and impart maximum viscosity to the yogurt. The photomicrograph in Figure  6 reveal the dramatic shearing effect on the starch granules when the pre­heat temperature  is increased from 150 degrees F to 180 degrees F (65 degrees C to 82 degrees C). Figure 6. – Unfragmented granules (low pre­heat) vs fragmented granules (high pre­heat) Experimental Matching of Processes and Starches The common process variables within the pre­heat and homogenization steps formed the framework for an experimental design recently conducted at National Starch and  Chemical Co. (NSC). The purpose of this study was to evaluate yogurts made with different starches  under the extremes of conditions at these two critical stages (Table 1).

Table 1 ­ Experimental Design Conditions Pre­Heat Temperature Homogenization Pressure (psi) (degrees F) (degrees C) (psi) (bar) 150 65 500 35 150 65 2500 170 180 82 500 35 180 82 2500 170

A variety of NSC waxy maize and tapioca starches covering a range of inhibition levels  were evaluated in this experimental design (see Table 2.) Food starch is also commonly  attained from regular maize, potato, and rice sources as well, but flavor, functionality stability, and cost  often Page 10 prevent their usage in yogurt. Yogurt manufacturers typically use waxy maize­based  starch in yogurts, and all of the waxy maize starches evaluated are currently used by commercial manufacturers. Tapioca starches, on the other hand, are less popular within the U.S. due  to a history of producing unacceptable graininess in yogurts. National Starch however has  developed a number of specialty tapioca starches to address this graininess problem, and so tapiocas  were also included in these experiments.

Table 2 ­ List of starches evaluated Base Name Processing resistance Waxy Maize PURITY® W Low Waxy Maize FRIGEX® W Medium Waxy Maize THERMFLO® Medium­High Waxy Maize PUREFLO® Medium­High Waxy Maize THERMTEX® Very High Tapioca

NATIONAL® 78­0148 Low Tapioca NATIONAL FRIGEX® HV Medium Tapioca NOVATION® 3300 Medium­High Tapioca PURITY 87 High Tapioca THERMSHEAR® Very High The yogurts made for this experimental design were processed according to typical Swiss  style yogurt processing conditions and were evaluated organoleptically by a trained panel for  body and texture/smoothness. A summary of the sensory results, along with comments on the  post­ processed microscopic evaluation of the starches, is given in Table 3. These results reveal  the dramatic effects that the process variations have on the final yogurts. Table 3. – Results comparison table Page 11 Results ­ Waxy Maize­Based Starches Yogurts made with the waxy maize­based starches that were processed using the 150  degrees F preheat condition generally had good­excellent scores for body/viscosity regardless of the homogenization pressure that followed. The microscopic evaluations of these starches  revealed a large majority of intact granules; evidence that the starches did not swell with the  relatively low preheat temperature and were therefore able to withstand the pressures of both the low  and high­ homogenization conditions. Under the high (180 degrees F) pre­heat condition, however,  the

yogurts were generally lower in body and were weak, with runny textures. As the  microscopic evaluation attests, this was due to severe fragmentation of the starch granules ­­­ a result  of having been homogenized after being partly swollen. The loss of body under these harsh processing conditions is especially evident in yogurts containing starches such as  PURITY W starch and FRIGEX W starch, which are considered less process resistant. These  starches swelled to a greater degree in the 180 degrees F pre­heat and were therefore more  susceptible to shear at the homogenizer than more inhibited products, like THERMFLO starch, and  especially THERMTEX starch. While fragmentation did occur with the THERMFLO and  THERMTEX starches, it was not as severe as experienced by the less inhibited starches. This enabled THERMTEX and THERMFLO starches to retain more of their viscosity functionality in  the yogurts. In fact, yogurt containing THERMTEX starch exhibited nearly the same body  under the most severe processing configuration (180 degrees F/2500 psi) (82 degrees C, 172 bars)  as the Page 12 least severe processing condition (150ºF/500 psi) (66 degrees C, 34 bars). This  demonstrates the remarkable process tolerance of a highly inhibited starch, despite granule fragmentation.  The graphs in Figure 7 illustrate this feature by contrasting the performance of THERMTEX  starch and FRIGEX W starch under various conditions. From this information, one can  conclude that as the manufacturing process severity increases, so must the starch's inhibition, or level of  cross­ linking, to obtain the most functionality from the starch. Fig. 7 – FRIGEX W starch vs THERMTEX starch cube plot Results ­ Tapioca­Based Starches

The yogurts made with tapioca­based starches showed similar trends to those made with  waxy starches, especially with respect to body/viscosity loss with the higher temperature preheat/homogenization configurations. For example, NATIONAL 78­0148 and  NATIONAL FRIGEX HV starches, which are considered low­medium process resistant starches, gave excellent body with the 150 degrees F preheat condition but then dropped off  dramatically once the preheat temperature and homogenization pressure were increased to 180 degrees F  and 2500 psi respectively. In contrast, yogurt made with PURITY 87 starch, a highly inhibited  product, only suffered a slight loss of body when processed under the most harsh configuration.  (see Figure 8.) Figure 8 – PURITY 87 starch vs N. FRIGEX HV starch cube plot Page 13 Microscopic evaluation revealed the fragments of the PURITY 87 starch to be  significantly less sheared than those of the less inhibited starches, demonstrating the starch's higher  tolerance to the effects of homogenization at a high temperature. It should be noted that  THERMSHEAR starch, which has an extremely high degree of inhibition, also displayed minimal  fragmentation under the most harsh configuration, but due to its very high modification level was unable  to adequately swell during pasteurization to develop an acceptable body. So, unless there is  an unusually high amount of shear involved in the process, a starch with too much process resistance may also not be desirable, since pasteurization temperatures rarely exceed 200  degrees F in commercial yogurt manufacturing. The classic graininess in yogurts that tapioca starches are known to contribute was  evident with NATIONAL 78­0148 and NATIONAL FRIGEX HV starches, regardless of process configuration or the integrity of the starch granules. As a result, textures for these  yogurts were

scored quite low. Yogurts containing NOVATION 3300, PURITY 87, and  THERMSHEAR starches on the other hand, produced very smooth, high quality textures. In general,  starch granule fragmentation with these treatments was also minimal. These results indicate that  more highly inhibited tapioca starches also tend to produce yogurts with smoother, glossier  textures. This trend was also seen in the yogurts made with the waxy maize­based starches.  Although to a lesser degree than with the tapiocas, more graininess was observed in those yogurts  containing the less inhibited starches (PURITY W and FRIGEX W) than with those containing more process tolerant starches. Conclusions Results from this work show that processing conditions can have a great impact on starch performance in Swiss style yogurts. A starch properly matched to the manufacturer's  specific processing conditions will result in a yogurt with good body and a high quality texture.  An Page 14 improperly matched starch can result in lower body, a poor texture, and inconsistent  production for the manufacturer. In general, lower preheat temperatures (150 degrees F or lower)  prior to homogenization reduce the likelihood of fragmenting the starch granule. This translates  into greater thickening power and smoother yogurt textures. Therefore manufacturers should  strive to ensure their preheat temperature is below 150 degrees F. A process flow with  homogenization prior to pasteurization is also desirable from a starch functionality perspective, as it also  reduces the likelihood of granule fragmentation. If these two conditions are met, product  developers can usually match a starch to their pasteurization temperature and hold time conditions.  Starches with medium inhibition levels are generally recommended for relatively low pasteurization

temperatures (180­185 degrees F,) while highly inhibited starches are suggested for higher pasteurization temperatures (195­200 degrees F.) If, on the other hand, the developer is constrained to high preheat temperatures, or homogenization post­pasteurization, then  mainly highly inhibited starches, such as waxy maize­based THERMTEX starch or tapioca­ based PURITY 87 starch should be considered. Finally, it is evident from these experiments that high quality yogurt textures can be  achieved with certain tapioca starches; namely those with relatively high inhibition levels. The  benefits of using tapioca starch in the flavor and ingredient­sensitive yogurt are significant.  Tapioca starches are blander than waxy maize starches and allow more of the yogurt's flavor to be  perceived. They are also considered to impart an added creaminess to yogurt. In addition, consumers have  shown preference for labels with tapioca starch over corn starch, and because it comes from a  root source, there is the potential for "Kosher for Passover" labeling. Tapioca starches such as PURITY 87 and NOVATION 3300 now enable manufacturers to take advantage of these  bland flavor and labeling benefits without sacrificing quality. As an additional feature,  NOVATION 3300, a functional native tapioca starch that has the properties of a traditionally  modified food starch, carries the label declaration of "tapioca starch," and is ideal for yogurts with all­ natural formulations.