**Powdered Infant Formula:**

**An Overview of Manufacturing Processes**

**Introduction**

Powdered infant formula is manufactured by more than a dozen firms in 40
-- 50 processing plants worldwide. Although there are many plants that
produce this product, the manufacturing processes are very similar.
Powdered infant formula is manufactured using two general types of
processes: a dry blending process and a wet mixing -- spray drying
process. Some manufacturers use a combination of these processes. In the
combined process, a base powder (consisting mainly of protein and fat
components) is produced using the wet mixing and spray drying process
and then the base powder is dry blended with the carbohydrate, mineral
and vitamin ingredients. These processes have different risks and
benefits with respect to the potential for product contamination by
bacteria such as *Enterobacter sakazakii* or other harmful bacteria.
Each of these processes will be described below, with consideration
given to the potential for product contamination by harmful bacteria.

**Dry Blending**

In the dry blending process, the ingredients are received from suppliers
in a dehydrated powdered form and are mixed together to achieve a
uniform blend of the macro and micro nutrients necessary for a complete
infant formula product. Dry blending, including combined wet and dry
processes, offers some manufacturing advantages over wet blending --
spray drying. Dry blending is less capital intensive and more energy
efficient than wet mixing -- spray drying. Also, since dry blending does
not involve the use of water in the manufacturing process, the
processing line can be kept dry for long periods of time. In a dry
environment, bacteria are denied the water needed to support growth.
This reduces the chance that harmful bacteria will become established in
the plant environment in sufficient numbers to cause product
contamination. However, the microbiological quality of a dry-blended
product is largely determined by the microbiological quality of the
constituent dry ingredients. In a dry blending process, there is no heat
treatment to destroy bacteria in the final product. Thus, if one or more
ingredients in a dry-blended product are contaminated by even low
numbers of harmful bacteria, these bacteria are likely to be present in
the finished product.

The dry blending process begins with the receipt of the ingredients. The
ingredients are typically stored until they are tested for conformance
to specifications, including microbiological contamination. Since
microbiological contaminants may be present in low numbers and may be
non-randomly distributed within the lot, it is difficult to assure
microbiological quality by lot testing alone. Therefore, manufacturers
of dry-blended products try to develop and maintain close relationships
with their ingredient suppliers. Each supplier must produce their
product in a manner that assures that harmful bacteria will not
contaminate the finished ingredient. This is usually accomplished by a
combination of appropriate process controls and strict adherence to good
manufacturing practices.

Dry ingredients are blended in large batches (1, 000 to 5,000 lbs.) in a
ribbon blender or other large scale blending equipment. The ingredients
must be blended until the nutrients are uniformly distributed throughout
the batch. The blended product is then passed through a sifter to remove
oversize particles and extraneous material. The sifted product is then
transferred to bags, totes or lined fiberboard drums for storage. In
some cases, the powder is transferred directly to the powder packaging
line. At the packaging line, the powder is transferred to a filler
hopper that feeds powder into the can filling line. Filled cans are
flushed with inert gas, seamed, labeled, coded and packed into cartons.
Typically, finished product is held until it undergoes a final check for
conformance to specifications, including testing for microbiological
contaminants.

**Wet Blending -- Spray Drying**

In the wet blending -- spray drying process, ingredients are blended
together, homogenized, pasteurized and spray dried to produce a powdered
product. The pasteurization step destroys harmful bacteria that may be
present in the ingredients. Therefore, this process is much less
dependent on the microbiological quality of ingredients. This process
also has the advantage of ensuring a uniform distribution of nutrients
throughout the batch. However, the wet blending -- spray drying process
requires that processing equipment, including the spray dryer and
fluidized bed, be regularly wet cleaned. This frequent wet cleaning
provides the moisture needed by bacteria to grow and become established
in the plant environment. If not controlled, these bacteria can be a
source of product contamination. Manufacturers that use the wet blending
-- spray drying process typically partition their plants into wet
process and dry process areas and strictly limit the movement of people
and equipment between the wet and dry areas. Also, they strictly enforce
sanitation practices, particularly in the dry processing areas.

The wet blending -- spray drying process begins with the receipt of
ingredients from suppliers. As with the dry blending process,
ingredients are stored until they are tested for conformance to
specifications. Ingredients are blended with water in large batches
(1,000 -- 5,000 gallons) then pumped to a heat exchanger for
pasteurization. The severity of the pasteurization process varies among
manufacturers, but it is always sufficient to destroy the vegetative
cells of harmful bacteria. After pasteurization, the liquid is
homogenized. \[Note: Some manufacturers homogenize product prior to
pasteurization.\] After pasteurization, certain heat sensitive micro
nutrients (*e.g.*, vitamins, amino acids and fatty acids) are added to
the product. The microbiological quality of these nutrients is critical,
since the product may not receive further heating sufficient to destroy
harmful bacteria. After the addition of micro-nutrients, the liquid may
be concentrated by passing it through an evaporator or it may be pumped
directly to the spray dryer. If the product is evaporated, it is heated
to 145 -- 170°F during the process. In some cases, the concentrated
liquid may be cooled to less than 45°F and stored in a large tank
(10,000 -- 30,000 gallons) until needed. Prior to spray drying, the
product is pre-heated to 160 -- 200°F and passed through a high pressure
pump to the spray dryer nozzles. The product is atomized into the spray
dryer where the inlet air temperature ranges from 280 - 400°F, depending
on the dryer model and process requirements. The spray dryer may be
either a horizontal box-type dryer or a vertical funnel shaped dryer. As
the droplets of product pass through the dryer, water is evaporated and
the dry powder falls to the bottom of the spray dryer. The outlet
temperature of the dryer is approximately 220°F. The temperature of the
powder at the spray dryer outlet ranges from 110 -- 175°F. The warm
powder is passed through a fluidized bed where it is cooled by a stream
of chilled air. At the end of the fluidized bed, the powder has cooled
to approximately 70°F. Typically, HEPA-filtered air is supplied to the
spray dryer and fluidized bed to minimize the risk of product
contamination. After spray drying, the product may be agglomerated to
increase the particle size and to improve its solubility. The finished
powder is passed through a sifter then transferred to bags, totes or
silos for storage. In some cases, the powder may be transferred directly
to the powder packaging line. At the packaging line, the powder is
transferred to a filler hopper that feeds powder into the can filling
line. Filled cans are flushed with inert gas, seamed, labeled, coded and
packed into cartons. Typically, finished product is held until it
undergoes a final check for conformance to specifications, including
microbiological contaminants.