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 bacteria-produced 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 = 2 c or 1 1/4 c

Recipe 2

1 gal skim milk + 10.4 oz = 4 c or 2 1/4 c

1 qt skim milk = 2.6 oz = 1 c or 1/2 c

Recipe 3

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

Recipe 4

1 gal regular milk + 4.8 oz = 1 3/4 c or 1 c

1 qt regular milk + 1.2 oz = 1/2 c or 1/4 c

*NFDM = Nonfat dry milkgal = gallonoz = ouncec = 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 1HOW PROCESSING AFFECTS STARCH SELECTION FOR YOGURTby Jeffrey W. Foss

National Starch and Chemical Company, Bridgewater, NJ.Starch is an important ingredient in today's popular Swiss and French style yogurts, whichtogether define the growing stirred yogurt market segment. Stirred yogurts differ from thetraditional fruit-on-the-bottom (FOB) products in that they come with fruit and flavor pre-mixedinto 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 theyogurt mass in the cup. When used alone or as part of a stabilizer blend, starch is the preferredthickening agent in yogurt due to its creamy texture, processing ease, and low cost whencompared with other hydrocolloids. Yogurt processing conditions vary among dairymanufacturers, 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 productdeveloper to match the proper starch to the specific conditions to meet the targeted texture. First,a few basics on yogurt and its manufactureThough an important food staple to the Middle Eastern people for more than 5000 years, yogurthas only recently become popular in the United States, largely due to an increased appreciationof 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 thantriple of what it was 25 years ago, and can be expected to increase as yogurts containingbeneficial probiotic cultures are being increasingly touted for colonic health. Much of themarket's growth can also be attributed to manufacturers' ability to keep up with the evolution inconsumer preferences. A variety of new textures, colors, and packaging schemes have beenintroduced 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 madeeating 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 theirchildrens' lunch boxes. Yogurts with trendy dessert-like 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 aresuccessfully bridging this apparent paradox by enabling consumers to feel they are partaking of ahealthy dessert, and therefore getting the best of both worlds. This push towards more creamy,pudding-like textures has also triggered a greater demand for nondairy stabilizers, such asstarches, which are required to achieve these textures. This preference shift is at the expense ofthe FOB segment whose products are now considered by some as somewhat passé along side themore rich, creamy, and often colorful stirred types. Current market indicators show that stirredyogurts have about a 70% share compared with the FOB types.FOB YogurtsThe main difference between FOB and stirred yogurts is textural, with the former being veryfirm and cuttable, and the latter soft and slightly flowable. This difference is primarily due tochanges in the yogurts' final processing steps. With FOB style yogurts, the pasteurized milkslurry is inoculated with cultures, and then pumped warm directly into its final consumer

Page 2package (with or without fruit on the bottom,) where it is fermented. The pH drops duringfermentation and causes the milk's casein protein to coagulate and form a gel. After cooling, thiscup-set yogurt is firm and very cuttable, due to the gelled casein in the system. This cup-setmanufacturing method is considered the traditional way of yogurt making, with its roots inancient Mesopotamia when storing goats' milk in the warm climate often resulted in theformation of a curd. Due to the strong set of these yogurts, supplemental hydrocolloids orstabilizers are not often used. Without a stabilizer present to bind water though, a heavy wheyingoff usually occurs by the time the product reaches the consumer, having been accelerated by thejostling the product receives during distribution. Wheying off is considered a serious defect; notonly is the presence of free whey on the yogurt's surface visually unappealing, but manyconsumers incorrectly view the wheying off as a sign of spoilage. In turn, some consumers willpour off any free whey before eating the yogurt, especially if it is extensive, as in the case of

many non-stabilized, cup-set yogurts. Incidently, this whey contains substantial protein, and istherefore 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 thetexture becomes too firm. Also characteristic of cup-set yogurts is a somewhat chunky, grainyappearance after the yogurt is stirred.Stirred YogurtsIn contrast, stirred yogurts are smoother, and despite being less firm, more full-bodied afterstirring. To make a Swiss style yogurt, the pasteurized milk slurry is pumped into a large vat andfermented to the desired pH. After the fermentation is complete, the yogurt is cooled, blendedwith fruits and/or flavors, and packaged for sale. The pumping action disrupts the milk proteingel network, and without the use of an added stabilizer, would result in only a slightly thickenedfluid product with little set. Therefore, nondairy stabilizer blends, such as modified food starchand gelatin, are normally used to boost the viscosity to a pudding-like consistency, and deliverthe slight set that is characteristic of these yogurts. The starch in the blend also absorbs the waterin the yogurt system and prevents the whey separation typically found in the FOB yogurts.Texture MeasurementGraphs depicting product quality data and rheological measurements are used as a means ofpresenting product differences. These graphs, or icons, can serve as textural "fingerprints" foryogurts. The larger the spoke for each axis of the icon, the greater that attribute is expressed inthe product. The measurement of several rheological attributes offers a more completedescription of the yogurts' texture than single-point viscosity measurements (e.g. Brookfield,Bostwick, etc.) and/or subjective sensory terminology alone. Rheological graphs comparing thetexture of typical FOB and Swiss style yogurts are seen in Figure 1.

Page 3Data 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 andgraininess data. Firmness refers to the yogurts' stiffness; elasticity refers to the ability of theyogurts to recover after deformation; viscosity refers to resistance to flow under shear; andbreakdown refers to the size of deformation required to cause flow. Whey separation wasmeasured after the products were disturbed to simulate distribution; and the degree of graininesswas judged by a trained panel. These icons clearly display the textural differences in eachproduct as described above. Note that while the overall viscosity values are similar for eachproduct, the high initial firmness and breakdown values for the FOB yogurt reveal a rigid, highlycuttable texture relative to the Swiss style product, whose low firmness, low breakdown, andhigh elasticity values indicate a somewhat less cuttable, pudding-like texture. The lower wheyseparation 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 useof starches in such products. Much of this information also applies to starches for cup-setyogurts. A wide range of starches is available, and a proper understanding of their role andfunctionality is needed to choose the correct starch for the yogurt system.

Page 4Starch Modification and ProcessabilityAs starch is heated, its granules lose their crystalline micellular structure, imbibe water and swellto many times their original size. This swelling results in increased viscosity in the cookedmixture. Uncooked waxy maize starch granules measure 5 to 20 microns in diameter, whereasfully swollen granules can be 75 microns or more. A well-cooked 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 starchindustry uses pasting rheometers, like the Brabender Visco/Amylo/Graph. A starch suspension isheated in the unit's revolving cup through a preset temperature profile and forms a paste. Torqueexerted on a spindle positioned in the starch suspension is continuously recorded on a chart toproduce a pasting curve. This data is helpful in determining a starch's gelatinization onset

temperature, rate of thickening, peak viscosity, breakdown, and thickening (set-back) duringheating and cooling. Starch manufacturers often use this information for quality controlmeasurements, as well as to predict starch performance in a food application.Swollen (cooked) starch is sensitive to extended hold times at high temperatures and/orexcessive shear during processing. Heat and shear can cause swollen starch granules to ruptureand lose viscosity, unless the starch has been modified to withstand such conditions. A foodstarch 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 cross-linking and monosubstitution, or stabilization. For the high temperature, high shear yogurt manufacturing process,starches that have been cross-linked are generally required. The cross-linking treatmentstrengthens the starch granule and prevents it from over-cooking or over-shearing during harshprocessing. The more cross-linked a starch is, the more it is said to be inhibited, and the greaterits resistance to processing. In figure 2, there is a comparison of a Brabender viscosity profile ofa moderately cross-linked waxy maize starch to that of a non-cross-linked (native) waxy maizestarch under temperature conditions which simulate those experienced in yogurt manufacturing.Figure 2 – Brabender/Viscosity Curves - Cross-linked Waxy vs. Native Waxy

Page 5The cross-linked starch maintains its viscosity, while the native version breaks downsignificantly. Translated into the finished yogurt, the cross-linked starch would give higher body,while the native starch would produce a thin, unstable product. Because processing temperaturesand shear rates vary widely among dairy operations, it is important to choose a starch with theoptimal level of cross-linking.Stabilization, the other most common food starch modification, also improves starchperformance in yogurt. Stabilizing groups added to the starch block the reassociation of theamylose and amylopectin polymers within the granule, and maintain the starch's smooth textureand viscosity stability. For a yogurt system, this would translate into textural stability, as well asa 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 ofdairy 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 combinationof cross-linking and stabilization is usually required in the high temperature, high shear yogurtmanufacturing process.In general, under processing conditions involving lower temperature, pressure and shear, starcheswith a medium level of inhibition are recommended, whereas for processes with highertemperature and shear, highly inhibited starches are needed. It is important, however, to look

Page 6closely at specific control points within the process since they can vary widely among yogurtmanufacturers. These variations can greatly affect starch functionality and influence the type ofstarch to use.Typical Swiss Style Yogurt Formulation and Manufacturing ProcessA formulation for a typical Swiss-style, lowfat yogurt is given in Figure 3.Figure 3 - Swiss formula(1% Milkfat)IngredientsPercent weightSkim milk (Standardized to 1.2 percent milkfat)89.65Sugar5.00Non-fat dry milk2.80When protein concentrate (34 percent protein)1.00THERMTEX® starch (by National Starch andChemical Company)1.20Gelatin (225 bloom)0.35Total100.00After 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 pre-heating phase which

further dissolves the ingredients and helps in the achievement of the final pasteurizationtemperature. The pre-heating temperature of the slurry often depends upon the efficiency of theplant's heat regeneration system, and can vary between 150 degrees F and 180 degrees F (65-82degrees C). After the pre-heat, the slurry (also referred to in the industry as the white mass mix)is homogenized, normally between 500 and 2,500 psi (35-175 bar). The purpose ofhomogenization 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 sizereduction of the ingredients in the mix, particularly the milk fat. Homogenization involvesforcing a mix through a small orifice or passageway. As the passageway size is reduced and theflow rate is maintained, pressure builds and particles break apart as they pass. This makes themix more "homogeneous." The higher the pressure, the greater the particle size reduction.Homogenization is often more effective when done twice, because low-particle-size fat globulestend to agglomerate. A two-stage homogenizer is therefore often employed to break up thoseagglomerates. Fat particle sizes of 5 microns or lower are normally achieved under moderatehomogenization pressures (1000/500 psi,) and adequately stabilize the milk fat in yogurtapplications. After homogenization, the mix is pasteurized (typically with a plate heat exchanger)to between 185 degrees F and 200 degrees F (85-93 degrees C) and held at this temperature for30 seconds to 5 minutes or more with holding tubes. This is referred to as HTST (HighTemperature, Short Time) pasteurization. A plate heat exchanger (PHE) consists of a pack ofparallel stainless steel plates in which the product (milk slurry) and the hot media (steam heatedwater) flow along the surface of alternate plates in adjacent streams. These plates are corrugatedin a pattern to provide turbulence for maximum heat transfer efficiency, and thus achieve athorough cook of the slurry. PHEs are able to maintain the high pasteurization temperaturesrequired 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 degreesF (41-43 degrees C), and inoculated with live bacterial cultures. Cooling the mix to thistemperature range is crucial to ensure the cultures' viability. The inoculated mix is then incubatedwithin 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, whichcoagulates the milk causing it to set. The lactic acid development is also responsible for theyogurt's characteristic tart flavor. Once the pH has dropped to about 4.5-4.6, the yogurt is brokenby tank agitation and pumped through another heat exchanger to rapidly cool it to between 50degrees F and 85 degrees F (10-30 degrees C). The yogurt is also often pumped through a screenor smoothing valve to give a smoother texture before being mixed with fruit, and packaged andrefrigerated. Figure 5 illustrates the above process.

Page 8Figure 5.Processing and Starch ChoiceAlthough the process flow described above is the most common in the industry, other variationsare sometimes used. For example, some manufacturers homogenize the white mass mix afterpasteurization; some do not homogenize at all. Some do not preheat. Some manufacturers batch-pasteurize, for instance with a steam-jacketed kettle, employing LTLT (Low Temperature LongTime) pasteurization. Process flow differences among manufacturers are often due tomanufacturing volume, equipment and/or facility limitations, or necessary accommodations forrunning other dairy products (which require the alternate flows) on the same production lines.When considering a starch recommendation, process flows are evaluated case-by-case, takinginto account the sequence of pasteurization and homogenization, as well as the temperatures andstresses involved.The two control points in the manufacturing process most critical to starch functionality are the

pre-heating and homogenization steps. The starch gelatinization(swelling onset) temperature insweetened milk is about 155 degree F (68 degrees C). Pre-heating the white mass mix to 180degrees F (82 degrees C,) which is well above the starch's gelatinization temperature, will begin

Page 9to swell the starch. The partly swollen starch is then vulnerable to the shear imparted duringhomogenization, especially if the homogenization pressure is high (>2000 psi) (138 bars).Granules that are partly or fully swollen (in the order of 25-75 microns in diameter) are fragile,and are significantly more prone to damage during homogenization. This shearing can fragmentthe starch granule and significantly reduce its thickening capacity, resulting in a yogurt with lowbody. This generally requires the manufacturer to use a greater-than-necessary amount of starchor stabilizer blend in the formula to achieve the targeted viscosity. An even more dramatic lossof viscosity would be evident if the homogenization followed pasteurization rather than precededit in the process flow. The starch granules, already fully swollen from the pasteurizationtemperature, would be completely torn apart by the shear, and contribute even less towardsviscosity. So, while homogenization is an important step in yogurt manufacturing it can bedevastating to the starch if done at too high a temperature.On the other hand, pre-heating the mix to only 150 degrees F (65 degrees C) or lower will notswell the starch, and the unswollen starch granules, because of their small size and highmicellular strength, will generally withstand the homogenization process, even if the pressure ishigh. The intact starch granules will then swell with minimal fracturing during the pasteurizationheating step and impart maximum viscosity to the yogurt. The photomicrograph in Figure 6reveal the dramatic shearing effect on the starch granules when the pre-heat temperature isincreased from 150 degrees F to 180 degrees F (65 degrees C to 82 degrees C).Figure 6. – Unfragmented granules (low pre-heat) vs fragmented granules (high pre-heat)Experimental Matching of Processes and StarchesThe common process variables within the pre-heat and homogenization steps formed theframework 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 theextremes of conditions at these two critical stages (Table 1).Table 1 - Experimental Design ConditionsPre-Heat TemperatureHomogenization Pressure (psi)(degrees F) (degrees C)(psi) (bar)150 65500 35150 652500 170180 82500 35180 822500 170A variety of NSC waxy maize and tapioca starches covering a range of inhibition levels wereevaluated in this experimental design (see Table 2.) Food starch is also commonly attained fromregular maize, potato, and rice sources as well, but flavor, functionality stability, and cost often

Page 10prevent their usage in yogurt. Yogurt manufacturers typically use waxy maize-based starch inyogurts, and all of the waxy maize starches evaluated are currently used by commercialmanufacturers. Tapioca starches, on the other hand, are less popular within the U.S. due to ahistory of producing unacceptable graininess in yogurts. National Starch however has developeda number of specialty tapioca starches to address this graininess problem, and so tapiocas werealso included in these experiments.Table 2 - List of starches evaluatedBaseNameProcessing resistanceWaxy MaizePURITY® WLowWaxy MaizeFRIGEX® WMediumWaxy MaizeTHERMFLO®

Medium-HighWaxy MaizePUREFLO®Medium-HighWaxy MaizeTHERMTEX®Very HighTapiocaNATIONAL® 78-0148LowTapiocaNATIONAL FRIGEX® HVMediumTapiocaNOVATION® 3300Medium-HighTapiocaPURITY 87HighTapiocaTHERMSHEAR®Very HighThe yogurts made for this experimental design were processed according to typical Swiss styleyogurt processing conditions and were evaluated organoleptically by a trained panel for bodyand 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 thedramatic effects that the process variations have on the final yogurts.Table 3. – Results comparison table

Page 11Results - Waxy Maize-Based StarchesYogurts made with the waxy maize-based starches that were processed using the 150 degrees Fpreheat condition generally had good-excellent scores for body/viscosity regardless of thehomogenization pressure that followed. The microscopic evaluations of these starches revealed alarge majority of intact granules; evidence that the starches did not swell with the relatively lowpreheat temperature and were therefore able to withstand the pressures of both the low and high-homogenization conditions. Under the high (180 degrees F) pre-heat condition, however, the

yogurts were generally lower in body and were weak, with runny textures. As the microscopicevaluation attests, this was due to severe fragmentation of the starch granules --- a result ofhaving been homogenized after being partly swollen. The loss of body under these harshprocessing conditions is especially evident in yogurts containing starches such as PURITY Wstarch and FRIGEX W starch, which are considered less process resistant. These starchesswelled to a greater degree in the 180 degrees F pre-heat and were therefore more susceptible toshear at the homogenizer than more inhibited products, like THERMFLO starch, and especiallyTHERMTEX starch. While fragmentation did occur with the THERMFLO and THERMTEXstarches, it was not as severe as experienced by the less inhibited starches. This enabledTHERMTEX and THERMFLO starches to retain more of their viscosity functionality in theyogurts. In fact, yogurt containing THERMTEX starch exhibited nearly the same body under themost severe processing configuration (180 degrees F/2500 psi) (82 degrees C, 172 bars) as the

Page 12least severe processing condition (150ºF/500 psi) (66 degrees C, 34 bars). This demonstrates theremarkable process tolerance of a highly inhibited starch, despite granule fragmentation. Thegraphs in Figure 7 illustrate this feature by contrasting the performance of THERMTEX starchand FRIGEX W starch under various conditions. From this information, one can conclude that asthe 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 plotResults - Tapioca-Based StarchesThe yogurts made with tapioca-based starches showed similar trends to those made with waxystarches, especially with respect to body/viscosity loss with the higher temperaturepreheat/homogenization configurations. For example, NATIONAL 78-0148 and NATIONALFRIGEX HV starches, which are considered low-medium process resistant starches, gaveexcellent 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 2500psi 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. (seeFigure 8.)Figure 8 – PURITY 87 starch vs N. FRIGEX HV starch cube plot

Page 13Microscopic evaluation revealed the fragments of the PURITY 87 starch to be significantly lesssheared than those of the less inhibited starches, demonstrating the starch's higher tolerance tothe effects of homogenization at a high temperature. It should be noted that THERMSHEARstarch, which has an extremely high degree of inhibition, also displayed minimal fragmentationunder the most harsh configuration, but due to its very high modification level was unable toadequately swell during pasteurization to develop an acceptable body. So, unless there is anunusually high amount of shear involved in the process, a starch with too much processresistance may also not be desirable, since pasteurization temperatures rarely exceed 200 degreesF in commercial yogurt manufacturing.The classic graininess in yogurts that tapioca starches are known to contribute was evident withNATIONAL 78-0148 and NATIONAL FRIGEX HV starches, regardless of processconfiguration or the integrity of the starch granules. As a result, textures for these yogurts werescored quite low. Yogurts containing NOVATION 3300, PURITY 87, and THERMSHEARstarches on the other hand, produced very smooth, high quality textures. In general, starchgranule fragmentation with these treatments was also minimal. These results indicate that morehighly inhibited tapioca starches also tend to produce yogurts with smoother, glossier textures.This trend was also seen in the yogurts made with the waxy maize-based starches. Although to alesser degree than with the tapiocas, more graininess was observed in those yogurts containingthe less inhibited starches (PURITY W and FRIGEX W) than with those containing moreprocess tolerant starches.Conclusions

Results from this work show that processing conditions can have a great impact on starchperformance in Swiss style yogurts. A starch properly matched to the manufacturer's specificprocessing conditions will result in a yogurt with good body and a high quality texture. An

Page 14improperly matched starch can result in lower body, a poor texture, and inconsistent productionfor the manufacturer. In general, lower preheat temperatures (150 degrees F or lower) prior tohomogenization reduce the likelihood of fragmenting the starch granule. This translates intogreater thickening power and smoother yogurt textures. Therefore manufacturers should strive toensure their preheat temperature is below 150 degrees F. A process flow with homogenizationprior to pasteurization is also desirable from a starch functionality perspective, as it also reducesthe likelihood of granule fragmentation. If these two conditions are met, product developers canusually match a starch to their pasteurization temperature and hold time conditions. Starches withmedium inhibition levels are generally recommended for relatively low pasteurizationtemperatures (180-185 degrees F,) while highly inhibited starches are suggested for higherpasteurization temperatures (195-200 degrees F.) If, on the other hand, the developer isconstrained to high preheat temperatures, or homogenization post-pasteurization, then mainlyhighly inhibited starches, such as waxy maize-based THERMTEX starch or tapioca-basedPURITY 87 starch should be considered.Finally, it is evident from these experiments that high quality yogurt textures can be achievedwith certain tapioca starches; namely those with relatively high inhibition levels. The benefits ofusing tapioca starch in the flavor and ingredient-sensitive yogurt are significant. Tapioca starchesare blander than waxy maize starches and allow more of the yogurt's flavor to be perceived. Theyare also considered to impart an added creaminess to yogurt. In addition, consumers have shownpreference for labels with tapioca starch over corn starch, and because it comes from a rootsource, 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 blandflavor and labeling benefits without sacrificing quality. As an additional feature, NOVATION3300, a functional native tapioca starch that has the properties of a traditionally modified foodstarch, carries the label declaration of "tapioca starch," and is ideal for yogurts with all-naturalformulations.