T hickeners are what turn sweetened cream into panna cotta,
make crème anglaise into a molded Bavarian, and gel fresh fruit juices
in pies. Starches, gelatin, and gums are also used in low-fat recipes to
replace eggs, a higher-fat source of thickening power. Thickeners
provide structure and stability to foods that are ephemeral, such as
whipped cream and meringue. Since thickeners come from many
different sources, each type has different properties that make it
suitable—or not—for one dish or another.
S TA R C H E S
Starches have many functions in baked goods, puddings, and sauces.
They help stabilize the delicate structure of soufflés, and they prevent
egg custards from curdling (see Chapter 15). The starch present in
flour, when broken down, serves as food for yeast in bread doughs, thus
aiding fermentation (see Chapter 2). Starch gelatinization in bread
doughs and cakes forms an important part of the supporting structure
of baked goods (see Chapters 12 and 14). Starch can also be used to mod-
erate the protein strength of flour, since adding starch to flour reduces
the percentage of gluten-forming proteins. Thus, substituting starch
for a small portion of strong flour can make a more tender crumb.
Not only does this reduce the ratio of protein to starch but also the
crumb becomes more tender because the starch competes with gluten-
forming proteins for water (Chapter 14).
103
104 Understanding Baking
This section, however, is concerned with the thickening property of
starches. Starches are used to thicken fruit-based desserts such as pies,
cobblers, and crisps, as well as for thickening custards, such as pastry
cream. Not all starches behave the same way. Some are best for dishes
that will be frozen and thawed; others are better for giving fruit fill-
ings a clear shine. It is up to the chef to determine which starch to use
in a specific application.
G E L AT I N I Z AT I O N
Gelatinization describes in one word what starches do: When heated,
they absorb moisture, swell, and thicken liquids, forming a gel-like
structure. Some starches can absorb 100 times their weight in water.
Starches are found in the seeds of grains and in the roots of plants.
Plants create starch as a form of energy reserve. Through photosynthe-
sis a plant produces glucose, which fuels its cells, and extra glucose is
converted to starch for storage. Starches are very long chains of glucose
molecules. In Chapter 3 sugar was defined as a simple carbohydrate
compared to starch. Granulated sugar, sucrose, is composed of one mol-
ecule of glucose and one molecule of fructose. The starches described
below range roughly from 10,000 to 50,000 glucose molecules each,
varying according to their plant source. To be botanically correct, what
cooks refer to as “root starches” are usually tubers. A tuber is a thick
part of the root or rhizome that stores plant food, or starch.
Starches are considered semicrystalline in structure and are dis-
cussed as granules. They can vary in shape as well as length. Straight
molecules are called amylose, branched ones are called amylopectin.
Each shape behaves differently when heated and cooled, providing dif-
ferent thickening characteristics. Grain seeds and roots vary in their ra-
tios of amylose to amylopectin. In general, grain-derived starches are
higher in amylose and root-derived are higher in amylopectin. Grain
starches have at most 30 percent amylose, and tubers, with the excep-
tion of potatoes, have much less.
Unlike sugars, starches do not dissolve in water at room temperature
but must be heated before they can swell and thicken. As a starch-
thickened sauce slowly heats, the starch granules absorb water and be-
Thickeners: Starches, Gelatin, and Gums 105
G R A I N S TA R C H E S V S . R O OT S TA R C H E S
The serving temperature, storage conditions, and desired finished appearance of
the product will determine whether you thicken with a grain starch (wheat flour,
rice flour, or cornstarch) or a root starch (arrowroot, tapioca, or potato).
FILLINGS THICKENED FILLINGS THICKENED
W I T H G R A I N S TA R C H E S W I T H R O O T S TA R C H E S
Will weep when frozen Will freeze and thaw without weeping
Will appear opaque when cooled Will thin if reheated
Will thicken into a firm gel as they cool Thicken at a lower temperature (around
Gelatinize just below a boil and can be 170°F)
brought to a boil Will be thickest when hot and slightly
Can be reheated without danger of thinner when cool
thinning Range from clear to translucent and
Can tolerate moderate stirring while hot shiny when cool
(before it is cool and set) Will thin if stirred too much
gin to swell. If the sauce has been thickened with flour or cornstarch,
the starch granules reach the gelatinization range beginning at 140°
and 145°F (lower for root starches). At this point, the granules are so
swollen with water that they no longer resemble granules but gels. All
of this is invisible to the naked eye, of course, since sauces seem to be ei-
ther thin or suddenly thick. The greatest viscosity is reached when the
overloaded starch granules burst. For grain starches, this will occur be-
tween 175° and 205°F, but for root starches, such as potato, this can oc-
cur under 170°F. When the starch granules burst, more starch leaks into
the sauce and contributes to thickening. The empty starch shells are the
primary source of thickening: Their size prevents quick and easy
movement through the sauce. So long as they are not deflated by vig-
orous stirring as the mixture cools, the sauce remains thick. Amylose,
which is straight, has better thickening ability than the branched
106 Understanding Baking
amylopectin. Its long shape, when swollen, makes amylose more likely
to collide with other molecules and get tangled up. Amylopectin,
though branched, moves with the ease of a round object through
liquid. Amylose, on the other hand, is more like a long swollen cater-
pillar that gets in the way.
Below is a list of common thickeners. Keep in mind that starch and
flour are not interchangeable terms. Corn flour, for example, will con-
tain protein and minerals in addition to starch. Potato starch is derived
from potatoes, but potato flour is the whole peeled potato, dried and
pulverized. Tapioca and arrowroot are referred to as flours, however.
WHEAT FLOUR is not pure starch, usually having around 10 per-
cent protein. Naturally, low-protein flours have more starch and are
better thickeners. The presence of protein makes flour less efficient as
a thickener than pure starches. Pure wheat starch, though less available,
can be used as an alternative. In general, it takes almost twice as much
flour to thicken as any of the other grains or roots listed below. Flour,
though, is the standard since it is universally available in pastry
kitchens, so all other starches are compared to it. Flour, like all grain
starches, must be well cooked or it will leave a raw cereal aftertaste.
CORNSTARCH is the preferred starch in American recipes, proba-
bly because it is readily available. In Europe it may be called cornflour,
a term in the United States that refers to finely ground cornmeal. Fruit
juices in pies thickened with it are translucent rather than opaque, un-
like flour, though not as clear as root-based thickeners. Cornstarch
must be fully cooked or it will leave an unpleasant pasty, raw taste be-
hind. Cornstarch used to thicken custards is usually mixed with a small
amount of liquid to form a paste to prevent it from forming lumps.
WA X Y C O R N S T A R C H is almost 99 percent amylopectin, and thus
behaves more like a root starch than a grain starch. It has little of the
cereal taste of regular cornstarch, and pies made from it will not weep
after being frozen.
RICE STARCH is derived from rice flour. It is less commonly used
in this country than other grain starches, though rice flour, which has
Thickeners: Starches, Gelatin, and Gums 107
no gluten, is sometimes added to cookies such as shortbread to create an
even more tender, crumbly texture. Rice starch has almost twice the
thickening power of flour.
POTATO STARCH is widely used in European cooking. Though
American bakers have also adopted the tradition of using mashed po-
tatoes, starchy potato cooking water, and even instant potato flakes
(with additional water) in baked goods for tenderness and added mois-
ture, pure potato starch comes after flour, cornstarch, and tapioca as a
preferred thickener. European chefs, however, prefer potato starch
since it has no cereal flavor, and because it swells and gels at a lower
temperature than flour or cornstarch. In cakes, potato starch can be
substituted for a portion of flour to “soften” it, since starch has no pro-
tein. A cake batter with potato starch will finish cooking at a lower in-
ternal temperature, which keeps the cake moist by reducing cooking
time, and has none of the raw taste it would have if cornstarch had been
used. Since cornstarch requires higher gelatinization temperatures, the
cake would have cooked longer and potentially lost more moisture.
Potato starch falls in between the grain and root starches in tempera-
ment: It has a little less amylose than flour (23 percent) and has more
amylopectin than the other roots. Potato starch has over twice the
thickening power of flour.
TAPIOCA, derived from the cassava plant, is the thickener of choice
for juicy berry pies, since it does not cloud the color of the fruit and
thickens beautifully. Tapioca flour and the instant tapioca granules
both work well; however, the instant granules take on a noticeable
globular texture if there is not enough liquid provided by the fruit
juices. Because instant tapioca granules require moisture to dissolve,
they remain hard on the surface of lattice-topped pies where they are
directly exposed to the dry air of the oven. Tapioca flour, since it is
finely ground, dissolves more easily and evenly. It has twice the thick-
ening power of flour.
ARROWROOT FLOUR comes from the starch of a tropical tuber
believed to be native to South America. It has almost twice the thick-
ening power of flour, and is perfectly clear and tasteless.
INSTANT STARCHES are specially processed (basically pre-
cooked) so they have the ability to swell and thicken cool liquids. One
instant starch sold under the brand name Clearjel is made from waxy
cornstarch, which makes it particularly useful for fillings and pies that
Thickeners: Starches, Gelatin, and Gums 109
has no real flavor, so it lets the other flavor components shine. Like
some starches, gelatin can hold 100 times its weight in water. Liquids set
with gelatin will hold their shape when unmolded. Used in modera-
tion, gelatin is a wonderful stabilizer, but too much makes mousses and
chiffon pies rubbery. A perfect Bavarian, for example, should just
barely hold its shape. The moment it hits the tongue it should dissolve
into a light creaminess. If it does not melt immediately, the tongue reg-
isters the resistance as a rubbery sensation, indicating too much gelatin.
Gelatin is an animal protein derived from the collagen in skin and
the connective tissues, such as tendons and cartilage. Most gelatin is
processed from pig skin. For those who avoid animal or pork products,
a gum (see below) is the most suitable replacement.
There are two forms of gelatin: leaf (or sheet) and powdered. Pow-
dered gelatin comes both in .25 ounce envelopes (about 21⁄4 teaspoons
each) and in bulk containers. One teaspoon of Knox brand powdered
gelatin is the equivalent of two sheets of gelatin. The sheets are stan-
dardized, so that one sheet has the same gelling capacity as another de-
spite differences in thickness or dimensions. Powdered gelatins are not
equal; each has a bloom rating to express gelling power.
H OW G E L AT I N WO R K S
Powdered gelatin must be sprinkled over a small amount of cool water
or liquid, such as cream or an alcohol like bourbon or rum (but prefer-
ably not highly acidic juices, which inhibit gelatin), for a minute or
two to soften— 1⁄4 cup liquid for 2 teaspoons gelatin is sufficient. The
liquid is then gently heated until the gelatin dissolves. It is advisable
to check with your fingers to ensure that the gelatin is completely
dissolved, since even small granules will form larger rubbery spots
when set.
Sheet gelatin is soaked in cold water for 10 minutes to soften. It is
then squeezed to drain it of the soaking water and gently melted in the
liquid called for in the recipe.
The gelatin mixture should be cooled until it just begins to set before
it is folded into delicate egg-white foams or cold whipped cream. If you
are diligent about frequent stirring, this can be done quickly over an
ice water bath, or more slowly in the refrigerator. Gentle stirring pre-
vents the mixture against the side of the bowl from setting faster than
110 Understanding Baking
the rest. If the gelatin sets too quickly, creating lumps, simply reheat it
until it is completely dissolved, providing the beaten whites or
whipped cream have not been added. Gelatin can be reheated with no
ill effect so long as it is not boiled. High heat reduces its thickening
power.
Large amounts of sugar and acidic fruits have an inhibiting effect
on gelatin’s ability to gel, but when a dessert completely refuses to set,
an enzyme in the fresh fruit may be the culprit. Enzymes in fresh
pineapple, figs, papaya, kiwifruit, honeydew melon, mangoes, and gin-
ger interfere with gelatin. However, cooking these fruits to 185°F will
destroy the enzyme. Canned fruit is not a problem, since its processing
denatures any inhibiting enzymes.
GUMS
Gums have several different functions in a bakery. They can be used as
thickeners or stabilizers, much like starches or gelatin. In certain ic-
ings, the addition of gum will prevent cracking or stickiness. Gums
may be used in reduced-fat baked goods to improve texture and prevent
moisture loss. The addition of gum can retard the crystallization of
sugar, and it can function as an emulsifier. Gums prevent weeping
(called syneresis—the release of liquid from a gel) of egg-based cus-
tards and fruit pie fillings. And finally, gums are used to make gum
paste, a malleable substance that can be formed into decorative flowers
or shapes for wedding cakes.
Gums fall into three categories: those derived from terrestrial
plants, alginates (seaweed), and those commercially produced by mi-
crobial fermentation. There are many gums used in commercial bak-
ing today (see Table 7.1), and the list below covers just a few that might
be accessible for commercial bakeries.
TERRESTRIAL PLANTS
G U M T R AGA C A N T H is derived from an Asian plant. Usually sold
in powder form, it is used in combination with confectioners’ sugar,
Thickeners: Starches, Gelatin, and Gums 111
TA B L E 7 . 1 C O M M E R C I A L G U M S
Marine Terrestrial Microbial Polysaccharide
Plants Plants Polysaccharides Derivatives
Agar Guar gum Dextran Carboxymethyl
cellulose
Alginates Gum arabic Gellan gum Methyl hydroxy-
propyl cellulose
Carragheen Gum tragacanth Rhamsan gum Hydroxypropyl
cellulose
Furcellaran Karaya gum Welan gum Hydroxyethyl
cellulose
Locust bean gum Xanthan gum Propylene glycol
alginate
Pectin Hydroxypropyl guar
Modified starch
Xanthan: Natural Biogum for Scientific Water Control, third edition. Rahway, N.J.: Merck and
Co., 1988. (Kelco is a division of Merck and Co.)
water, shortening, and food colors to make gum paste flowers and dec-
orations for specialty cakes.
A L G I NAT E S
AGAR - AGAR , also called Japanese gelatin, is a powdered, tasteless
derivative of seaweed. It is often used in place of gelatin for those who
keep kosher or are vegan. If substituting for gelatin, less agar-agar will
be needed as it has greater thickening capacity.
CARRAGHEEN comes from dark seaweed off the coast of Ireland
and is sometimes called Irish moss. It may be used much the same way
as agar-agar.
112 Understanding Baking
MICROBIAL GUMS
These gums are important to large-scale industrial food production
but are rarely used by the typical pastry chef. The names of some of
these gums, such as Xanthan and Dextran, may sound familiar since
they are common ingredients in packaged mixes, candies, and snack
foods.
