Day 10
Thickening and Gelling Agents
Milk and Dairy Products

• Polysaccharides
• Thickening
• Gelling
• Type A gelatin
• Sheet or leaf gelatin
• Bloom rating
• To bloom gelatin
• Vegetable gum
• Amylose
• Amylopectin
• Starch granule
• Cereal starch
• Root starch
• Modified food starch
• Instant starch
• Gelatinization
• Starch retrogradation

Introduction
To thicken or gel a food product:
– Add an ingredient that is already thick.
• Sour cream, cream cheese, jams and jellies, syrups, fruit purees.
• Besides thickening, these ingredients add color, flavor, and nutrients.
– Add an ingredient used exclusively for thickening and gelling.
• Gelatin.
• Vegetable gums.
• Starches.
– Form an emulsion. Example: heavy cream.
– Form a foam. Example: whipped cream.
– Add eggs.

Thickening and Gelling
Thickening occurs when water and other molecules or particles move around slowly.
Example: Pectin or other large molecules bump and loosely tangle.
Gelling occurs when water and other molecules or particles are prevented from moving around at all.
Example: Pectin or other large molecules bond or tightly entangle.

Thickening and Gelling
Almost any large molecule can thicken.
– Polysaccharides are very large molecules
• Made of many (poly) sugar molecules (saccharides) linked together.
Examples: Starch, vegetable gums.
– Proteins are very large molecules
• Made of many amino acids linked together.
Example: Gelatin.
– Many, but not all, molecules that thicken will gel when used at a high enough level.
• Cornstarch thickens at low levels, gels at high levels.
• Guar gum thickens at low levels, becomes gummy but does not gel at high levels.

Gelatin
Gelatin
– Forms an appealing crystal clear gel.
Caution: gelatin forms lumps if not properly tempered into cold mixtures.
– Melts quickly and cleanly in mouth.
Caution: gelatin forms tough, rubbery gels if used at too high a level.
– Is an animal protein.
• Not allowed in strict vegetarian diets.
• Sources of gelatin:
– Pigskin (Type A gelatin).
– Cattle bones and hides (Type B gelatin).
– Fish (isinglass).
• Type A gelatin, from pigskin, is by far the most common; not allowed in kosher (Jewish) or halal (Islamic) diets.

Gelatin
Gelatin gels as it cools.
• Tiny strands slow, coil up, tangle, and stack up into fragile junctions.
• Water gets trapped within this three-dimensional web.
• Fragile gel is easily dissolved with body heat.

Gelatin
Gelatin (Type A) is produced in a series of steps.
1. Chopped cleaned pigskins are soaked in cold acid.
• Breaks down connective tissue: Rigid, ropelike collagen protein fibers are transformed into smaller invisible strands of gelatin.
2. Hot water is used for dissolving gelatin and extracting it from pigskins.
• Process is repeated up to six times.
• Each extraction occurs at a progressively higher temperature.
• As extraction temperature increases, quality of gelatin goes down.
• Gelatin solution is purified, concentrated, and formed into sheets or noodles.
3. Sheets or noodles are dried and ground into powder.

Gelatin
Sheet gelatin:
– Is also called leaf gelatin.
– Is made by further processing powdered gelatin.
• Powdered gelatin is redissolved then cast into a thin film.
– As with powdered gelatin, sheet gelatin is available in different grades, or Bloom ratings.
Bloom rating is a measure of gel strength.
– Most gelatin ranges from about 50 to 300 on the Bloom scale.
– The higher the Bloom rating, the firmer the gel and the faster it sets. Also,
• The lighter, clearer it appears and the milder it tastes.
• The shorter, less stringy the gel.

Gelatin
Bloom rating
– Of common powdered gelatin is about 230.
– Of sheet gelatin is often designated by the name of a precious metal.
• Silver and bronze sheet gelatin are most common types in North
America.
Notice the weight of the sheet changes with the Bloom rating. If a formula calls for ten sheets, use ten sheets, no matter the Bloom rating.

Gelatin
How to Use
1. Bloom gelatin first, so it is less likely to clump.
• To bloom gelatin means to add it to a cold liquid to hydrate.
• Use almost any cold liquid; water is most common.
Caution: Raw pineapple and kiwi juice contain an enzyme, a protease, that breaks down and liquefies gelatin.
Caution: Liquids high in acid, like lemon juice, can weaken gelatin, although they will not completely liquefy it.
• Wait 5 to 10 minutes, for gelatin to fully absorb water.
2. Heat the bloomed gelatin gently, or add to hot liquid, to melt.
Caution: Do not overheat, or gelatin could weaken.

Gelatin
Differences between powder and sheets
– Bloomed differently.
• Sheets are typically added to excess water, then removed and gently squeezed.
Example : Take care that water is room temperature or cooler, so sheets do not dissolve completely.
• Powdered gelatin is typically added to a measured amount of cold water.
– Measured differently.
• Sheets are typically counted.
– Easy to do with small amounts.
– With large amounts, easier to weigh.
• Powder is weighed.

Gelatin
Switching between different grades of sheet gelatin
– When counted, make a one-for-one substitution.
Example: If a formula calls for five gelatin sheets, use five sheets of any grade gelatin; manufacturer adjusts weight per sheet, to compensate for different gel strengths.
– When weighed, account for differences in Bloom ratings by adjusting weights.
Example: Instead of 100 grams of bronze sheets, use 76 grams of silver sheets:
100 grams ÷ 3.3 grams/bronze sheet = 30.3 sheets X 2.5 grams/silver sheet

Gelatin
Switching between sheet and powdered gelatin
– An approximate conversion is as follows:
17 sheets = 1 ounce (28 grams) gelatin powder.
– Conversion depends on actual Bloom rating of powdered gelatin.
• Always prepare a test batch to confirm that conversion works; adjust as necessary.
Note: water for blooming gelatin is generally listed in formulas that call for powdered gelatin but not for formulas calling for sheets bloomed in excess water.

Vegetable Gums
Vegetable gums
– Are polysaccharides that absorb large quantities of water.
– Some thicken only; some also gel.
• Are not gummy when properly used.
– Examples:
• Pectin.
• Agar.
• Carrageenan.
• Guar gum and locust bean gum.
• Gum arabic.
• Gum tragacanth.
• Xanthan gum.
• Methylcellulose.

Vegetable Gums
Pectin
– High in certain fruits: apples, plums, cranberries, raspberries, citrus peel.
• Can be made into jams and jellies without added pectin.
– Produces attractive clear gel, with clean flavor and pleasant mouthfeel.
– Can purchase pure pectin as dry powder.
– Requires proper amount of sugar and acid to gel.
– Uses: mirrors, glazes, jams and jellies, bakery fillings, fruit confections.

Vegetable Gums
Agar
– Also called agar-agar, or kanten.
– Extracted from red seaweed.
– Purchase as strands, flakes, or dry powder.
– To use: boil until dissolved.
• Strands are first soaked in water, to soften.

Vegetable Gums
Agar (cont.)
– Nicknamed the “vegetable gelatin.”
• Forms clear gels, similar to gelatin.
• Cannot be whipped as gelatin can.
• Used in place of gelatin whenever dietary or religious restrictions warrant its use.
• Much less agar is needed than gelatin: start with conversion of 8:1, or eight parts gelatin to one part agar.
– Uses: piping gels, gelled confections and desserts, for stabilizing icings and fillings, as a substitute for gelatin (in non-aerated products).

Vegetable Gums
Guar gum and locust bean gum
– Extracted from the endosperm of beans.
– Locust bean gum is also called carob gum.
– Uses
• In ice cream and frozen pasteurized egg whites, to thicken and prevent ice crystal growth.
• In cream cheese and sour cream, to thicken, add creaminess, and prevent separation of liquid.

Vegetable Gums
Xanthan gum
– From the fermentation of a microorganism.
– Forms a flexible film that traps air and leavening gases.
– Provides flexibility to doughs; helps them hold together.
– Main use in bakeshop: gluten-free baked goods.

Starches
Starch molecules
– Polysaccharides consisting of many glucose units bonded together.
– Two types.
• Amylose; straight-chained.
• Amylopectin; branched.

Starches
Starch granules
– Small gritty particles tightly packed with starch molecules.
– Found in
• Cereal grains.
– Examples: corn, rice, wheat.
• Roots and tubers.
– Examples: potatoes, arrowroot, and yuca (also called cassava or manioc).
– Vary in size and shape, depending on the starch.
• Potato granules are relatively large and oval; cornstarch granules are much smaller and more angular.
– Grow larger as the plant ages.
• Starch molecules are arranged as concentric rings within the granule, much as growth rings form on a tree as it matures.

Starches
Different starches have different properties because of differences in
– Size and shape of granules.
– Amount of amylose/amylopectin or size of molecules.

Starches
Cereal starches
– Extracted from endosperm of corn, rice, wheat.
– Cornstarch is most common.
• Inexpensive and readily available.
• A general purpose starch.
• Compared to many other starches, is high in amylose.
• Has some disadvantages over certain other starches:
– Cloudy.
– Not stable in freezer.
– Has a cereal taste; masks flavors.

Starches
Root starches
– Extracted from the tubers (roots) of plants.
• Potato, arrowroot, yuca.
– In general, are lower in amylose and higher in amylopectin.
– Use instead of cornstarch:
• Where clarity, clean flavor, and a soft gel are desirable.
• In gluten-free baked goods.
– Gelatinize sooner than cornstarch, for less grittiness.

Starches
Tapioca is most common root starch.
– Extracted from yuca, also called cassava or manioc.
– Processed into pearls, for use in sauces and pie fillings.
• Require soaking, sometimes for hours or overnight; quick-cooking granules require only short soaking.
• Reduces stringiness.

Starches
Modified food starch
– Starch is treated with chemicals to modify its properties.
– Main reason for use: stability.
• Less likely to thin out when exposed to too much heat or acid.
• Less likely to tighten and weep when frozen.
– Any starch can be modified, but many modified starches are made from waxy maize starch.
– Some are cook-up starches and others are instant.

Starches
Instant starch
– Thickens and gels without heat.
– Most are also modified, for stability.
– Also called pregelatinized or cold-water swelling starch.
– To use: Slowly add to cold liquids, while whisking or stirring.
• If necessary, blend dry starch with about four parts sugar or other dry ingredient, to prevent clumping.
– Uses: for last-minute thickening; for heat-sensitive products.

Starches
Starch gelatinization
– Occurs when starch is heated in presence of water.
• Granules lose their orderliness and swell from large amounts of water moving in.
• Water becomes trapped inside swollen granules, causing liquids to thicken.
– Too much heat results in degraded granules and a loss of thickening.

Starches
For maximum thickening and gelling:
– Cook for the proper length of time.
• Follow formula’s method of preparation carefully.
• In general, cornstarch mixtures are boiled gently for two-three minutes.
– Need granules to swell and trap water but do not want granules to degrade.

Starches
Cook time will depend on:
– Type of starch.
• Root starches typically gelatinize sooner than cornstarch.
– Presence of tenderizers.
• Sweeteners and fats slow down the cooking of starch because they slow the swelling of granules.
• With formulas high in sugar, withhold half the sugar until after starch has gelatinized.
– Presence of acid.
• Acid speeds up the cooking of starch because it breaks apart starch granules and breaks down starch molecules.
• With formulas high in acid, reduce cook time, increase the amount of starch, or add acid after mixture is cooked and cooled. Or, use a modified food starch.

Starches
Starch molecules bond over time, once cooled.
– Process is called retrogradation.
– In creams and pie fillings,
• Gel shrinks and toughens.
• Weeping often occurs, where water squeezes out of tightening gel.
• Especially likely to occur:
– With cornstarch-based products.
– When products are frozen.
– In baked goods,
• Crumb stales, that is, it becomes dry, hard, and crumbly.
• Especially likely to occur
– With products made from lean doughs, such as baguettes.
– When products are refrigerated.

Providing a thickened or gelled texture.
– Thickening and gelling are forms of structure building.
• Starch, in particular, contributes to the structure of baked goods.
– Increasing stability.
• Thickening and gelling agents are sometimes called stabilizers, meaning that they prevent undesirable changes from occurring in foods.
Examples: gelatin and whipped cream; guar gum and frozen egg whites .

Providing gloss or sheen to sauces, fillings, and glazes.
– Many thickening and gelling agents form a smooth layer that clings to the surfaces of ingredients.
– Smooth layers reflect light in a way that provides gloss or sheen.
Example: mirror glazes on cakes, made with gelatin or pectin.
Additional Functions
– Softening and tenderizing baked goods.
– Absorbing moisture.

Storage and Handling
Store gelatin, gums, and starches covered.
– Prevents them from absorbing moisture and clumping.
To use: separate dry particles (gelatin, gum, or starch) before heating.
– Blend with other dry ingredients, such as granulated sugar.
• Rule of thumb: use about four parts sugar with one part dry starch.
– Blend with fat, such as butter or oil.
– Add first to cold water, to hydrate.
• Works with cook-up starches, gelatin, agar and many gums.
• Does not work with instant starches.

• Pathogenic microorganisms
• Pasteurization
• Homogenization
• Emulsion
• Casein
• Whey
• Lactose intolerance
• Cultured dairy products
• Lactic acid bacteria

Commercial Processes
• Pasteurization.
– Heat treatment to eliminate pathogenic (diseasecausing) microorganisms.
– Different methods:
• High-temperature, short-time (HTST); most common means.
• Ultra-high-temperature (UHT); also called ultrapasteurization.
– Longer shelf life but slightly different flavor.

Commercial Processes
• Homogenization.
– Prevents cream from separating and rising to top of milk.
– Milk forced through small openings:
• Breaks milk fat into tiny droplets.
• Forms a stable emulsion.
Effect of homogenization on milk fat in whole milk (a) unhomogenized, (b) homogenized

Commercial Processes
• Separation.
– Milk is spun fast in a separator; separates cream from milk.
• Separator is a type of centrifuge; works like a salad spinner.
• Cream is lighter, less dense; spins off from heavier milk.

Commercial Processes
The ability to separate out the fat from milk allows for a range of products with different milk fat contents.

Makeup of Milk
Milk is composed of:
– Mostly water.
– Milk fat and molecules dissolved in it, including:
• Small amounts of emulsifiers, carotenoid colors, rich dairy flavors.
– Milk solids not fat (MSNF), including:
• Protein, lactose (milk sugar), ash (minerals).

Makeup of Milk
Two main types of milk proteins:
– Casein proteins:
• Provide opaque whiteness to milk.
• Thicken and gel as they coagulate; easily coagulated with acids or enzymes.
– Important in the manufacture of cheeses, yogurt, sour cream.
– Whey proteins:
• In clear greenish liquid called whey.
• Form a film along pan bottoms and surface of heated milk; to prevent: add sugar to milk and stir as it heats.

Makeup of Milk
Lactose:
– Milk sugar.
• Provides slight sweet flavor to milk.
• A disaccharide; consists of glucose and galactose.
– Lactose intolerance: intestinal discomfort after consuming milk and milk products.
• Body does not contain enough of the enzyme lactase to break down lactose into glucose and galactose.
– Yeast are lactose intolerant, that is, they cannot ferment lactose.

Milk Products
Fluid Milk
– Classified by its fat content.
• Whole milk is highest in milk fat: 3.25% or higher.
– Best for freshest dairy flavor.
• Use in baked custards, cream pies, custard sauce, ice cream, pastry cream.
– Usually heated before added to yeast doughs.

Milk Products
Dry Milk
– Also called DMS: dry milk solids. Two types:
• High heat DMS; in yeast doughs and other baked goods.
• Low heat DMS; in ice cream, to increase milk solids.
– Made by removing most of the water from whole or fatfree milk.
• Fat in whole dry milk oxidizes easily to rancid off-flavor.
• Fat-free (nonfat) dry milk, NFDM, has a longer shelf life.
– Advantages over fluid milk: takes up less space and needs no refrigeration.
– To use: blend with dry ingredients or cream with butter or shortening.

Milk Products
Cream
– Usually UHT pasteurized, for extended shelf life.
– Richer flavor, thicker consistency than milk.
– Heavy cream (36 – 40% milk fat) forms the most stable whipped cream.
– Light cream can be made by mixing equal parts heavy cream and whole milk.

Cream (cont.)
Milk Products

Milk Products
Evaporated and Sweetened Condensed Milks
– Purchased in cans; shelf stable.
– Low-fat and fat-free versions available.
– Both made by removing water from milk.
• Evaporated milk contains twice the milk fat and twice the MSNF as whole fluid milk.
• Sweetened condensed milk has additional water removed and contains added sugar.
– Are not interchangeable.
• Sweetened condensed is thicker, sweeter, denser; has more caramelized color and flavor. Can be used in Mexican flan.
– Uses: pumpkin pie, smooth fudge, caramel, as a cream substitute.

Milk Products
Cultured Dairy Products
– Are fermented products, made by adding live bacteria
“cultures.”
• Most common bacteria culture: lactic acid bacteria, which ferment lactose into lactic acid.
– Generally tolerated by those with lactose intolerance, because they are low in lactose.
– Includes:
• Cultured buttermilk.
• Yogurt.
• Sour cream.
• Crème fraîche.
• Clotted cream.

Milk Products
Cheeses
– Made by forming curds and separating out the liquid whey.
• Curds consist of coagulated casein proteins, with some liquid whey still trapped inside.
– Most are cultured dairy products; live bacteria produce the acid that coagulates the casein.
– Ripened (aged) or unripened (fresh, not aged).
– Most common in bakeshop: unripened cheeses.
• Cream cheese, Neufchâtel, baker’s cheese.
• Ricotta.
• Mascarpone.
• Quark.

Main Functions
– Increasing crust color.
• From Maillard browning of milk proteins and sugar (lactose).
– Delaying staling.
– Increasing crust softness.
• Bread made with milk will have soft rather than crisp crust.
– Blending flavors and providing richness in flavor.
– Providing fine, even crumb to baked goods.
– Forming a stable foam.
• Cream whips into foam, stiffened and stabilized by solid fat crystals.
• Milk proteins whip into foam; example: cappuccino froth, whipped evaporated milk.

Other Functions
– Aiding in the creaming of shortening.
• Dry milk solids only.
– Absorbing moisture.
• Adding DMS to doughs requires the addition, ounce for ounce, of additional water.
– Aiding in the coagulation of egg proteins.
• Custards made with water (or soy, almond milks) are not as firm as those made with milk.
– Providing moisture.
• Milk is mostly water (about 88% water).
• Heavy cream is over 50% water.
– Adding nutritional value.

Storage and Handling
All milk products absorb odors; cover properly.
• Fluid milk:
– Spoilage bacteria can grow and sour milk; discard.
– Light causes flavor changes, loss of vitamins.
• Cultured dairy products: have longer shelf life.
– Will become increasingly sour over time.
– Mold can grow; discard.
• Soft, unripened cheeses
– High in moisture and highly perishable (will mold).
• Nonfat DMS:
– Can clump; keep cool and dry, and sift, if necessary.

LABS
• All Groups:
• Panna Cotta
• Strawberry Sauce
• Pate choux
• Gr 3- Whip 1# Mascarpone
• Gr 4- Whip 1# Mascarpone/ 4 oz. heavy cream

Lab
• Panna Cotta- Amount of Gelatin
• Gr 1: 1 % powder
• Gr 2: ½ % powder
• Gr 3: 1 ½ % powder
• Gr 4: Leaf- 1% (1 leaf= 1.5 g powder)

Lab
• Strawberry Sauce 1 oz/pint
• Gr 1: Corn starch
• Gr 2: Arrowroot
• Gr 3: Potato starch
• Gr 4: Cake flour
• MOP: Make slurry with starch, 1 oz. sugar and 5 oz puree
• Bring puree to boil- add slurry- bring to boil- boil 2 minutes

Pate Choux
• Pg. 371
• Gr 1- Milk
• Gr 2- Water
• Gr 3- Milk; Butter
• Gr 4- Water, Butter