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235
13
Sour Cream and Crème Fraîche
Lisbeth Meunier-Goddik
13.1 Introduction
Sour cream is a relatively heavy, viscous product with a glossy sheen. It has a delicate, lactic acid taste
with a balanced, pleasant, buttery-like (diacetyl) aroma (Bodyfelt 1981). Various types of sour cream are
found in many regions of the world. The products vary with regard to fat content and by the presence
or absence of nondairy ingredients. Furthermore, both cultured and direct acidications are utilized to
lower pH. This chapter covers sour cream as it is produced in the U.S. and its French counterpart—crème
fraîche.
13.2 Sour Cream
13.2.1 Definition
The U.S. Food and Drug Administration (FDA) [21 Code of Federal Regulations (CFR) 131.160] denes
sour cream as follows: “Sour cream results from the souring, by lactic acid producing bacteria, of
CONTENTS
13.1 Introduction .................................................................................................................................. 235
13.2 Sour Cream .................................................................................................................................. 235
13.2.1 Denition ......................................................................................................................... 235
13.2.2 Sensory Characteristics ................................................................................................... 236
13.2.3 Utilization ........................................................................................................................ 236
13.3 Fermentation ................................................................................................................................ 237
13.4 Gel Formation .............................................................................................................................. 237
13.5 Stabilizers ..................................................................................................................................... 238
13.6 Processing .................................................................................................................................... 239
13.6.1 “Shortcuts” ...................................................................................................................... 240
13.6.2 Artisan Production ..........................................................................................................240
13.6.3 Chymosin Addition .......................................................................................................... 240
13.6.4 Set Sour Cream ................................................................................................................ 240
13.6.5 Direct Acidication .........................................................................................................240
13.6.6 Low-Fat and Nonfat Sour Cream ....................................................................................240
13.7 Shelf Life ...................................................................................................................................... 241
13.8 Sensory Defects in Sour Cream ................................................................................................... 241
13.8.1 Flavor ............................................................................................................................... 241
13.8.2 Body and Texture ............................................................................................................ 242
13.9 Functional Properties ................................................................................................................... 242
13.10 Crème Fraîche .............................................................................................................................. 243
References .............................................................................................................................................. 243
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236 Handbook of Animal-Based Fermented Food and Beverage Technology
pasteurized cream. Sour cream contains not less than 18 percent milkfat;. . . . Sour cream has a titratable
acidity of not less than 0.5 percent, calculated as lactic acid.” If stabilizers are used, the fat content of
the dairy fraction must be at least 18% fat and above 14.4% of the entire product. Optional ingredients
permitted in sour cream are “(1) safe and suitable ingredients that improve texture, prevent syneresis, or
extend the shelf life of the product, (2) sodium citrate in an amount not more than 0.1 percent that may
be added prior to culturing as a avor precursor, (3) rennet, (4) safe and suitable nutritive sweeteners,
(5) salt, and (6) avoring ingredients, with or without safe and suitable coloring, as follows: (i) fruit and
fruit juice (including concentrated fruit and fruit juice) and (ii) safe and suitable natural and articial
food avoring.”
Consumers’ desire for decreasing dietary fat content has created a market for low-fat sour cream.
Among these products, reduced-fat, light (at least 25% or 50% fat reduction), and nonfat are common,
in part due to FDA’s labeling requirements for reduced-fat products (21 CFR 101). Sales data over the
past 25 years for the U.S. market (USDA 2010) are illustrated in Figure 13.1. The trend clearly shows
increased sales. In 2009, nearly 400 kg × 106 of sour cream was sold. Per capita sales of sour cream and
dips was 1.88 kg. In comparison, per capita sales for yogurt was 5.661 kg (USDA 2010).
13.2.2 Sensory Characteristics
Traditionally, the avor of sour cream was well characterized by “sour.” However, the trend for cul-
tured dairy products is toward a milder avor (Barnes et al. 1991) in part due to consumers’ dislike
of “too sour” fermented products (Thompson et al. 2007). Reduced acidity permits the sensation of
aromatic compounds produced by lactic acid cultures. Lindsay et al. (1967) found that important avor
compounds in sour cream include diacetyl, acetic acid, acetaldehyde, and dimethyl sulde. All aroma
compounds are associated with mesophilic heterofermentative starter culture metabolism (Vasiljevic
and Shah 2008). Sour cream is highly viscous and should be smooth and free of particulate matter. As
for appearance, a homogeneous, glossy surface is preferred, and no whey separation should be visible in
the container (Costello 2008).
13.2.3 Utilization
Sour cream is predominantly utilized as an accompaniment with warm entrees such as baked pota-
toes and burritos. This usage imposes certain demands on the sensory characteristics of the product,
especially with regard to texture when in contact with warm surfaces. Sour cream must remain viscous
without whey separation when placed on warm food. In addition, avor characteristics become less sig-
nicant when mixed with high-intensity savory avor notes such as those encountered in Mexican cui-
sine. In fact, for some usages, the absence of off-avors may be considered the primary avor attribute.
This general shift in emphasis away from avor toward texture has led to a renewed interest in a “back to
basics” sour cream such as crème fraîche, which is described later in this chapter.
0
100
200
300
400
500
600
700
1985 1990 1995 2000 2005
Sour cream and dips sales
(million kilograms)
FIGURE 13.1 Sale, in million kilograms, of sour cream and dips in the U.S. between 1975 and 2008. (From U.S.
Department of Agriculture (USDA). 2010. Economic Research Service Report. Agricultural Marketing Service,
Washington, DC. Available at www.ers.usda.gov/publications/LDP/xlstables/FLUIDSALES.xls (accessed 13 October
2010). With permission.)
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237Sour Cream and Crème Fraîche
Sour cream is frequently used as a base in dips and sauces. Traditionally, avors such as onion and
spinach have been popular. Currently, the trend is more diverse, with avors ranging from apricot ginger
to chipotle (Jones 2010).
13.3 Fermentation
As with all fermented dairy products, the choice of starter culture is crucial for the production of high-
quality sour cream (Folkenberg and Skriver 2001). Currently, the focus for sour cream starters is placed
on accelerating the activity to complete the fermentation within 12 h. Mixed strains of mesophilic lactic
acid bacteria are used for sour cream. In general, both acid and aroma producers are utilized. Acid pro-
ducers include Lactococcus lactis ssp. lactis and Lc. lactis ssp. cremoris. Lc. lactis ssp. lactis biovar.
diacetylactis (or Cit+ Lactococci) and Leuconostoc mesenteroides ssp. cremoris are commonly used
aroma producers.
Acid producers convert lactose into -lactate through a homofermentative pathway. They can produce
up to 0.8% lactic acid in milk (Cogan 1995) and are responsible for lowering pH in the fermented product.
In contrast, aroma producers are heterofermentative and can convert lactose into -lactate, ethanol,
acetate, and CO2. In addition, these strains convert citrate into diacetyl, which is one of the major a-
vor compounds responsible for typical sour cream avor. Diacetyl is subsequently partially converted
into acetoin, which is a avorless compound (Monnet et al. 1995). Extensive research at starter culture
companies have led to the development of Leuconostoc strains that show less of a tendency to convert
diacetyl into acetoin, thus retaining high levels of diacetyl. Diacetyl levels may be elevated by the addi-
tion of citrate (Levata-Jovanovic and Sandine 1997). The use of such strains can extend the shelf life
of sour cream, as it takes longer for the product to turn stale. Leuconostocs also reduce acetaldehyde to
ethanol (Dessart and Steenson 1995; Keenan et al. 1966). In fact, acetaldehyde has been shown to pro-
mote the growth of L. mesenteroides ssp. cremoris (Lindsay et al. 1965; Collins and Speckman 1974).
Acetaldehyde is typically associated with yogurt avor (green apple) but is considered an off-avor in
sour cream.
The choice of starter cultures will affect product texture as well. Strains of acid producers that increase
viscosity through the production of exopolysaccharides have been developed (Folkenberg et al. 2005).
These polysaccharide chains contain galactose, glucose, fructose, mannose, and other sugars. Quantity
and type depend on the bacteria strain and growth conditions (Duboc 2001; Ruas-Madiedo 2005). The
exopolysaccharides interact with the protein matrix, creating a rmer network and increasing water-
binding capacity. The importance of this behavior was conrmed by Adapa and Schmidt (1998), who
found that low-fat sour cream, fermented by exopolysaccharide-producing lactic acid bacteria, was less
susceptible to syneresis and had higher viscosity.
Production of high-quality sour cream requires a ne balance of acid, viscosity, and avor-producing
bacteria. While this balance varies among commercially available strains, a typical combination would
be 60% acid producers, 25% acid and viscosity producers, and 15% avor producers. However, fermenta-
tion conditions such as temperature and pH end point will impact the ratio during fermentation (Savoie
et al. 2007).
13.4 Gel Formation
Fermentation leads to a signicant increase in viscosity. Two physicochemical changes cause this behav-
ior (Fox et al. 2000; Walstra and van Vliet 1986). The casein submicelles disaggregate because of the sol-
ubilization of colloidal calcium phosphate. In addition, the negative surface charge on the casein micelles
decrease as the pH level approaches the isoelectric point. This creates the opportunity for casein micelles
to enter into a more ordered system. Temperature during fermentation impacts the rate of fermentation
and the viscoelastic properties of the gels (Lee and Lucey 2004). Besides the protein network, the cream
gains viscosity from the formation of homogenization clusters (Mulder and Walstra 1974). Following
single-stage homogenization at room temperature, milk fat globules will cluster, and these clusters may
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238 Handbook of Animal-Based Fermented Food and Beverage Technology
contain up to about 105 globules (Walstra et al. 1999). Casein molecules adsorb onto newly formed fat
globule membranes and, in the case of high fat content, form bridges between fat globules. Clustering
increases viscosity because (1) serum is entrapped between the globules and because of (2)the formation
of irregularly shaped clusters.
13.5 Stabilizers
The gel structure may not be sufciently rm to withstand abuse during transportation, handling, and
storage. This could result in a weak-bodied sour cream and whey syneresis in the container. These
defects are especially noticeable for low-fat products. To ensure consistent rm texture, dairy processors
can either build up milk solids by adding dairy proteins or, more often, choose to add nondairy stabilizers
(Hunt and Maynes 1997). Stabilizers commonly found in sour cream include different polysaccharides.
Stabilizers must be food grade and approved. The type and quantity used vary widely, depending
on the fat content, starter culture, and required sensory characteristics of the nal product. Types and
quantities of potential stabilizer mixtures used in sour cream are outlined in Table 13.1. In particular, the
nonfat formulation contains other ingredients such as emulsiers, color, and protein.
Polysaccharides bind water and increase viscosity. Commonly used plant polysaccharides include car-
rageenans, guar gums, and cellulose derivatives. Modied starches are frequently utilized as well. It
is necessary to fully hydrate these polysaccharides to optimize their functionality. Depending on the
ingredient, this may require efcient blending systems for the incorporation of the ingredient into the
cream, although care should be taken to avoid churning the cream. Complete hydration can sometimes
only be accomplished following heating and cooling steps, which are conveniently done by the pasteuri-
zation process. Time may also be a factor for hydration to occur. Besides binding with water molecules,
polysaccharides may also interact with milk proteins and form a network, which limits the movement of
water and increases viscosity. A short description of the stabilizers is provided below.
Carrageenans: Extract of seaweed. Three types of carrageenans are commercially available—
lambda, iota, and kappa—which differ based on the amount of sulfate. They have low viscosity at high
temperature, but viscosity increases during cooling. Lambda has the highest sulfate content, is soluble
in cold milk, and forms weak gels. Iota is soluble in hot milk (55°C) and prevents syneresis. Kappa only
dissolves in hot milk (<70°C) and forms brittle gels (Marshall and Arbuckle 1996).
Guar gum: Endosperm of seed from the plant Cyamopsis tetragonolobus. Different types of guar gum
are available to t processing conditions. Maximum viscosity develops over time. All are soluble in cold
milk. The main component is mannose with attached galactose units.
Methylcellulose: It is a cellulose that improves freeze–thaw stability and prevents melt upon heating
(Hunt and Maynes 1997).
Lately, the trend is toward natural sour cream. No stabilizers are added to this product, and instead,
body is improved by the addition of milk solids.
TABLE 13.1
Example of Stabilizer Used in Sour Cream
Product Stabilizers Usage Level
Sour cream Modied food starch, grade A whey, sodium phosphate, guar gum,
sodium citrate, calcium sulfate, carrageenan, locust bean gum
1.5%–3.0%
Light sour cream Same as above 1.75%–3.5%
Nonfat sour cream Modied food starch, microcrystalline cellulose, propylene glycol
monoester, gum arabic, articial color, cellulose gum
3.5%–6.5%
Source: Continental Custom Ingredients, Inc. 2002.Technical Bulletin Regarding Sour Cream Formulation and Processing.
Continental Custom Ingredients, Inc., West Chicago, IL 60185. With permission.
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239Sour Cream and Crème Fraîche
13.6 Processing
Throughout the processing of sour cream, extra care should be taken to protect the cream. Prior to
pasteurization, rough cream treatment could lead to rancid off-avors due to lipolysis. Following fer-
mentation, it is important to treat the coagulum gently to retain body and texture. This includes the use
of positive displacement pumps instead of centrifugal pumps, round pipe elbows instead of 90° angles,
and the use of gravity feed wherever possible. In addition, special cream pasteurizers may be used
(Figure13.2).
°
Mixing
Preheating (55°C)
Homogenization (10–25MPa)
Pasteurization (85°C 45 s)
Cooling (22°C)
Incorporation of starter culture
Fermentation in tank (12–16 hrs)
Breaking of coagulum (pH 4.6)
Cooling (12°C)
Homogenization (5–10 MPa)
Packaging
Storage (4°C)
Cream (4 C) Stabilizers
FIGURE 13.2 Process ow chart of a typical sour cream process.
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240 Handbook of Animal-Based Fermented Food and Beverage Technology
Ingredients can be incorporated directly into standardized cream by mixing equipment such as a
triblender. Another option is to incorporate the dry ingredients into the milk portion before standard-
izing the cream. The mix is preheated and homogenized (~65°C, 10–25 MPa; Kosikowski and Mistry
1999; Okuyama et al. 1994) immediately prior to pasteurization. Dairy homogenizers are normally
double stage to prevent homogenization clusters. However, in sour cream production, single-stage
homogenization is preferred to build up the body of the product. Homogenizing twice can build up tex-
ture but is inefcient. Instead, homogenization followed by passage through a shearing pump may be
utilized. Additional viscosity is obtained if the cream is homogenized downstream from the pasteurizer,
although such a process increases the potential for postpasteurization contamination. Pasteurization
is done at relatively high temperatures (85°C–90°C for 10–45 s), well above what is required for the
destruction of pathogens. The more severe heat treatment lowers the potential for oxidative and rancid
off-avors during storage, and it may help improve product viscosity due to the partial denaturation
of serum proteins. The cream is cooled to 22°C–25°C and pumped into the fermentation tank, and the
starter culture is added. Gentle mixing should continue until the culture and the cream are properly
mixed (maximum of 30 min). At this point, mixing is stopped until fermentation is complete. The
fermentation tank may be double jacketed to allow for better temperature control. However, in reality,
this is not essential if the temperature of the processing room remains relatively constant at around
22°C. Fermentation temperature may vary slightly from plant to plant. Higher temperatures lead to
faster fermentation and, potentially, a more acidic product, whereas lower fermentation temperatures
may give a more avorful product. The fermentation is slowed down/stopped by cooling when the
desired acidity (~pH 4.5 or titratable acidity around 0.7%– 0.8%) is achieved. Typically, this takes
14–18 h. The coagulum is broken by gentle stirring, and the product is cooled either by pumping cool-
ing water into the double-jacketed area of the tank or by pumping the cream through a special plate
cooler. The cream should be cooled to around 8°C–12°C, which slows starter culture activity before
packaging. Prior to packaging, it can also be passed through a homogenizer screen (smoothing plug)
or a similar type of ow restrictor to smoothen and improve texture (Continental Custom Ingredients
2002). The nal cooling to around 4°C must occur slowly in the package in the cooler in order to allow
the cream to obtain the appropriate viscosity. It is essential that the cream not be moved during this
cooling step.
The above process assumes a large-scale production. However, numerous process variations exist.
13.6.1 “Shortcuts”
Throughout the process described above, special attention is focused on the gentle treatment of the prod-
uct to assure proper body and texture. In reality, the stabilizers currently used permit more exibility in
the process. A certain amount of product abuse can be tolerated without lowering the product quality,
because the stabilizers, when properly used, create a rm texture and prevent whey separation.
13.6.2 Artisan Production
It is possible to signicantly simplify the process when producing small quantities of a product. Sour
cream can be made in a double-jacketed pasteurization tank which doubles as fermentation tank with
gravity feed to the ller. The absence of a nal in-line cooling step would require an efcient cooling
procedure for the packaged product.
13.6.3 Chymosin Addition
Low quantities of chymosin may be added at the same time as the starter culture. This creates a more
“spoonable” sour cream. Lee and White (1993) found that chymosin addition (e.g., 0.066 mL/L) to low-
fat sour cream resulted in increased viscosity and whey separation. Sensory scores were lower for the
chymosin-containing sour cream with regard to avor, body/texture, and appearance. This indicates that
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241Sour Cream and Crème Fraîche
it may be preferable to modify the stabilizer mixture rather than to add chymosin when trying to increase
product viscosity.
13.6.4 Set Sour Cream
The standardized, pasteurized cream can be mixed with starter culture and immediately lled into the
package. The cream is then fermented within the nal package, which leaves the coagulum undisturbed.
When the appropriate acidity is obtained, the products are cooled either by passing through a blast cooler
or by placement in a cooler. The advantage of this method is the possibility of lowering or eliminating
stabilizers and yet obtaining excellent body and texture. The disadvantages are the large space require-
ment for fermenting the packaged product and the relatively slow cooling.
13.6.5 Direct Acidification
A product somewhat similar to sour cream can be obtained by direct acidication by organic acids such
as lactic acid instead of fermentation. However, Kwan et al. (1982) and Hempenius et al. (1969) found
that sensory panelists preferred cultured sour cream instead of chemically acidied cream. Product tem-
perature at the time of acidication is critical and should be around 20°C–25°C. Higher temperatures
increase the likelihood that graininess occurs, and lower temperatures increase the time required for gel
formation (Continental Custom Ingredients 2002).
13.6.6 Low-Fat and Nonfat Sour Cream
Vitamin A fortication is required in these products. The processes are often similar to traditional sour
cream, although nonfat sour cream mix should be homogenized at a much lower pressure. The main dif-
ference is observed in the stabilizer mix as described in Section 13.5.
13.7 Shelf Life
Sour cream should have a shelf life of around 25–45 days. One study documents that, when properly
stored undisturbed at 4°C, sour cream has an acceptable shelf life of up to 6 weeks (Warren 1987). In
another study, Folkenberg and Skriver (2001) evaluated the change of sensory properties of sour cream
during storage time. As storage time approached 28 days, the intensity of prickling mouthfeel, sour odor,
and bitter taste increased. The samples were stored under ideal conditions, which suggest that real-life
distribution and storage temperature abuse would likely decrease the shelf life of this product below 28
days.
The single most important factor determining shelf-life is cream quality. Unless the cream is of excel-
lent quality, the sour cream quickly develops off-avors. Two parameters that impact cream quality are
(1) raw milk quality and (2) pretreatment of milk. Good-quality raw milk has low bacterial content (low
standard plate count) and comes from healthy cows (low somatic cell count). Even good-quality raw
milk spoils unless quickly cooled and kept at low temperatures until pasteurization. Furthermore, the
time interval between milking and pasteurization should be as short as possible to limit the growth of
psychotropic microorganisms. Other factors to consider are proper cleaning and sanitation of all milk
contact surfaces, well-installed and sized pumps, and no unnecessary milk handling.
Assuming that high-quality cream is utilized, the parameters that limit shelf life tend to be associated
with either avor defects or surface growth of yeasts and molds. When using appropriate stabilizers,
body and texture should remain adequate throughout the shelf life. A guide on how to prevent avor
defects is included below. Yeasts and molds are controlled by improving sanitation throughout the pro-
cess. As with many other dairy products, sanitation trouble spots are often associated with the ller
machines, which are difcult to clean properly.
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242 Handbook of Animal-Based Fermented Food and Beverage Technology
13.8 Sensory Defects in Sour Cream
13.8.1 Flavor
The high lipid content makes sour cream extremely vulnerable to lipid-associated off-avors such as
rancidity and oxidation. Other avor defects include atness, lack of cultured avor, and high acidity.
Rancid. Hydrolytic rancidity or lipolysis is caused by the release of free fatty acids from the glycerol
backbone of triglycerides. The reaction is catalyzed by the lipase enzyme, which can be a native milk
lipoprotein lipase or can originate from bacterial sources. Triglycerides are generally protected from
lipase activity, as long as the milk fat globule remains intact. However, damage to the globule will
lead to rapid lipolysis, because lipase, which is situated on the surface of the globule, gains access
to the triglycerides. Therefore, precautions must be taken to prevent damage to the milk fat globule
until pasteurization, which denatures most types of lipase. This means that raw milk/cream must be
pasteurized before or immediately after homogenization to assure denaturation of lipase. Likewise, it
is strongly recommended never to recycle pasteurized milk/cream back into raw milk/cream storage,
which is essentially an issue of rework handling. Cream from poor-quality raw milk can also develop
rancid off-avors during storage, as some bacterial lipases may be quite heat stable and not denature
during pasteurization.
Oxidized. Autoxidation of milk fat is a reaction with oxygen that proceeds through a free radical
mechanism. Unsaturated fatty acids and phospholipids are the prime substrates that are broken down
into smaller molecular weight compounds such as aldehydes and ketones. Oxidized cream exhibits
off-avors and aromas that have been characterized as cardboardy, metallic, oily, painty, shy, and tal-
lowy (Bodyfelt et al. 1988). Oxidation is catalyzed by divalent cations such as iron or copper. Thus, the
best prevention is to avoid contact of milk/cream with these metals. This requires attention to details,
as a single tting or pipe made of these metals can cause signicant autoxidation. Milk and cream can
be more susceptible to autoxidation following changes in the cows’ diet. For example, ax seed can
increase the content of polyunsaturated fatty acids in the milk. The feed and water can also be a source
of catalysts such as copper (Timmons et al. 2001). The problem is likely more evident toward the end of
winter, as the levels of antioxidants (e.g., vitamin E) in the feed tends to be lower.
Light-induced oxidation can also inuence avor characteristics of sour cream. Light-induced oxida-
tion is a defect associated with milk proteins and involves the degradation of milk fat, proteins, and
vitamins (Webster et al. 2009; Intawiwat et al. 2010). It has been demonstrated that the light barrier
properties of the packaging materials impact sour cream avor over the shelf life, with high-light
barrier properties minimizing the defect and low-light barrier properties leading to off-avors within
hours of exposure to uorescent light sources typically associated with retail conditions (Larsen et al.
2009).
Lacks ne or cultured avor. Both avor defects tend to be associated with the choice of starter cul-
ture. It may be possible to improve avor by switching to culture systems with more aroma-producing
capacity or to strains that retard the transfer of diacetyl into acetoin. It is also possible to add low concen-
trations of citric acid (below 0.1%), which is then converted to diacetyl by the aroma-producing starter
cultures. A slight change (usually decrease) in fermentation temperature has also been found to improve
the concentration of aroma compounds. The defect can also result from avors imparted by stabilizers.
Lowering the stabilizer dose or changing to another stabilizer system may be required.
Has high acidity. If the nal product pH is very low (e.g., around pH 4.0), the product gets an
unpleasant sour avor. While it is possible to stop the fermentation at a higher pH level, this does
not necessarily solve the problem, because slow fermentation continues in the cooled and packaged
product. Therefore, it is often preferable to change the starter culture mixture to lower the ratio of acid-
producing bacteria.
Bitter. Bitter off-avors are often indicators of excess proteolytic activity. Poor-quality raw milk may
contain heat-stable proteases that remain active throughout storage. The defect is especially noticeable at
the end of the shelf life. Improving raw milk quality, increasing pasteurization temperature, or shorten-
ing code dates are possible solutions (Folkenberg and Skriver 2001).
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243Sour Cream and Crème Fraîche
13.8.2 Body and Texture
As described above, texture is an essential quality parameter. Sour cream must remain highly viscous
when in contact with warm food surfaces such as baked potatoes.
Too rm or weak. Improper choice of stabilizers can cause overstabilized sour cream that clings to the
spoon. Alternatively, the sour cream can be weak bodied and “melt” on the hot food surface.
Grainy. Graininess is primarily a mouthfeel problem, although it can be visually distracting as well
in extreme cases. Grainy sour cream can be an indication of poor blending or incomplete hydration of
ingredients. A different choice of stabilizers or a modication of incorporation procedure may improve
the product. Another solution is to pass the product through a single-stage homogenizer valve prior to
packaging. Grains can also indicate that the fermentation was stopped at too high a pH level and the
caseins are at their isoelectric point around pH 4.6.
Free whey. Whey syneresis on top of the sour cream in the package is considered a signicant quality
defect. There are three solutions available to solving the problem: (1) change or increase the concentra-
tion of stabilizer, (2) increase fat content (higher fat sour creams have a better water-binding capacity) or
(3) reevaluate the entire process and eliminate points of product abuse. This would primarily include all
steps following fermentation.
13.9 Functional Properties
Although conjugated linoleic acid (CLA) is a minor component of milk fat, dairy is one of the major
sources of CLA in our diet. The CLA content in milk and dairy products varies greatly due to the cows’
diet and can range from 0.1% up to 2% of milk lipids (Khanal and Olson 2004). High intake of CLA has
been linked to decreased risk of several cancers and enhanced function of immune cells (Ip et al. 1994;
Krichevsky 2004). Moreover, data suggest that the consumption of dairy products high in fat such as sour
cream may reduce the risk of colorectal cancer (Larsson et al. 2005). Sphingolipids in dairy fats have
also been linked to anticarcinogenic effects. In addition, clearly higher fat dairy products such as sour
cream contain more of these benecial lipids (Ribar et al. 2007).
13.10 Crème Fraîche
Crème fraîche or, more correctly, crème fraîche épaisse fermentée is the European counterpart of the U.S.
sour cream product. Crème fraîche has fat content around 30%–45% and has a mild, aromatic cream avor.
The differences between the two products originate in the manner of usage. The usage of sour cream is
described above. Crème fraîche is used cold on desserts such as fruits or cakes, or warm as a foundation in
cream sauces that are commonly used in French cuisine. This double usage creates a unique demand for
specic product attributes. The dessert utilization requires a clean, not too sour (Barnes et al. 1991), cul-
tured avor that does not overpower avors from other dessert components. The cultured avor should be
refreshing so that it covers the impression of fat in the product. This emphasis on avor has led to signicant
research at starter culture and dairy processing companies to develop starter cultures that cause optimum
avor development. Body and texture should be smooth and less rm than sour cream. Crème fraîche
should be “spoonable,” not “pourable,” and should spread slightly on the dessert without being a sauce.
The incorporation of crème fraîche into a warm sauce requires thermostability; otherwise, the protein
would precipitate and occulate in the sauce. For regular crème fraîche (>30% fat), occulation is rarely
a problem. In contrast, low-fat crème fraîche (~15% fat) is less stable when heated. The addition of sta-
bilizers such as xanthan gum can stabilize low-fat crème fraîche. However, based on European labeling
legislation, crème fraîche cannot contain stabilizers, and a stabilized product would therefore need to be
marketed under another name.
Crème fraîche is produced by a process similar to that of sour cream, with the exception that no
ingredients are added. Without stabilizers, it becomes a challenge to obtain good body and texture.
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244 Handbook of Animal-Based Fermented Food and Beverage Technology
Each processing step requires attention to producing and maintaining high viscosity. In this case, the
homogenizer becomes an essential tool for building viscosity. Only single-stage homogenization is uti-
lized. The product is sometimes homogenized twice, either in subsequent runs before pasteurization or,
more commonly, both before and after pasteurization. Homogenization after pasteurization promotes
better viscosity and, equally important, better thermostability. An additional homogenization following
fermentation gives a homogeneous product with a smooth mouthfeel. Homogenization downstream from
the pasteurizer (i.e., after pasteurization) should raise concerns with regard to postpasteurization con-
tamination. Ideally, an aseptic homogenizer should be used. However, the high price of such homogeniz-
ers makes this an unsuitable alternative. Instead, great emphasis must be placed on the proper cleaning
and sanitizing of the downstream homogenizer. In addition, food safety issues are normally controlled
because of the high content of lactic acid bacteria and the low pH level.
There is some discussion as to the nal pH level of crème fraîche fermentée. Kosikowski et al. (1999)
and Kurmann et al. (1992) state that the cream is fermented to pH 6.2–6.3. However, commercially, it is
commonly fermented to an end pH around 4.5. The mild avor is not obtained by a higher pH but, rather,
through selection of aroma-producing starter cultures. It is the combination of aroma compounds and the
high fat content that mask the sour avor in crème fraîche.
Crème fraîche is a new product in the U.S. market. The high fat content and small-scale processing
contribute to a retail price that is at least twice as expensive as the traditional sour cream. The product is
frequently made by artisan dairy processors and is sold in outlets such as farmers’ markets and high-end
restaurants. Its increasing popularity is an indication of changing culinary habits promoted by growing
population diversity and exposure to other culinary culture.
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