En pratique: culture de surface

About molds: surface cultures

Application of molds

Commercial molds are available in liquid/frozen or powder form. The latter requires a presoaking to activate the spores and make them grow/ sporulate. Molds from Chr. Hansen are available in a freeze-dried powder form.

The inoculation dose in the form of dry spores should be soaked for two hours prior to use. After soaking the inoculation dose is added to non-chlorinated water to create the required suspension volume.

Dosage & yield per unit

The dosage is indicated on the pouch or bottle as a volume of liters of suspension to be prepared. In general, the number of sausages to be inoculated per volume of suspension depends on the diameter of the sausages.

Big diameter sausages give more tons per volume of suspension than small diameters. The suspension dilutes over time because the spores stick to the sausages and there are less and less spores in the suspension; this leads sometimes to less growth on sausages, which were inoculated at the end of a day or working period.

It takes a short observation period in order to find out how long a suspension will last in order to give an optimal result. As a rule of thumb: 10 liters of suspension may be enough for 4 tons of 100mm diameter sausage but only for 2 tons of 26/28 mm diameter sausages.

Most molds from Chr. Hansen comes in pouches for 50 liters of suspension.

Different ways of using the mold solution

As mentioned a good result depends on equipment or processes that enable regulation of relative humidity, temperature and airspeed, and secures uniform and effective coverage with molds.

The absence of effective coverage increases the risk of wild flora propagating.

Dipping in vats or tube (manually)

This system is simple and very effective for small units. The suspension has to be stirred from time to time to avoid clotting of spores; i.e. spores accumulating around solid materials fallen into the suspension.

The suspension should not be carried over from one day to the next due to the risk of propagation of wild yeasts. The sausages should be completely immersed in order to get an even cover. The dipping area and the rest of the facility should be separated in order to avoid accidental spread of the spores to the rest of the factory.

In addition, the installation of disinfection baths on the floor is recommended.

Shower's application (whole trolleys)

A shower unit with multiple shower heads is used to sprinkle the suspension over the sausages and an agitation and pumping unit secure a uniform suspension.

This unit should be in a separate area of the facility to avoid spread of spores. A dripping area with run-off collector and recycle drain feed the excess suspension back to the pumping system.

After sufficient dripping time trolleys are passed through pediluve or disinfection baths in the floor to clean the lower parts and avoid the spread of spores to the fermentation area and the rest of the factory.

Spray application (individual sausage)

A conveyer belt system moves the sausages into an enclosed area with an overhead spraying system being linked to a recycling pump and a collector tank for the run-off.

The sausages are kept in motion and turned continuously by mechanized rollers, which move the sausages through the enclosed area. The inlet and outlet of the enclosed area are “sealed” by flexible plastic strips.

This technique has the advantage of being highly productive, efficient in distributing the spores, occupying very little space, protecting the environment of the facility from contamination and it is easy to clean and sterilize.

Spray application in fermentation rooms

This method is used in small production units. The application equipment is a simple spraying unit used in plant/vegetable spraying.

It has some inconveniences like uneven distribution, and infestation of ducts and condenser units happens quite often, and the spores are spread by the feet of workers.

Handling precautions

Small pieces of solid matter like pieces of meat, string etc may fall into the suspension during operation. Spores have tendency to clot upon these solid materials and the suspension is heavily diluted.

The spraying nozzles may be blocked by the solids and less/no spores may be applied. Simple, relatively coarse filters limit the risk of solids in the suspension.

Technology effects on mold growth

The growth of molds is heavily affected by the environment under which the sausage is produced, and the technology applied.

Ideally, growth should appear within 2 days (white round dots), molds grow in a patchy form hence the importance to obtain an even distribution of spores. Yeasts grow in rod form and have a tendency to form longer chains.

If the growing conditions are adverse (cold, strong ventilation, dry) the mold spores may grow very slowly and there may be large patches without coverage; wild yeasts may take over.

In the following, the most important growth factors (enhancers and inhibitors) are mentioned.

Sausage technology and type

The ratio of fat and lean meat determines the moisture transfer to the casing and hence the growth conditions of the molds.

The size of the particles affects the drying of the surface and creates a more or less “bouncy“ surface. Big fat particles help create a “marbled“ appearance. Smearing due to wrong filling technique or any other cause may lead to uneven growth because of uneven evaporation.

The growth of molds helps diminish the risks/effects of dry rims and hence improves texture.

Influence of casing type

A great number of casing types are used in the industry (natural, fibrous, collagen types, etc).

These different casing types have a significant influence on the growth performance of the molds and this is mainly due to the humidity of the casing and its value as a growth “substrate“ (see table below).

Cellulose casings

Not ideal for molds because it is relatively dry; should be soaked before stuffing if possible; growth may need more time to reach adequate cover than on natural casings.

Sometimes wild molds and yeasts show cellulase activity which may lead to partial dissolution of casing (holes appear at peeling step;casing looks rough).

Peelable cellulose casings

Same as above, but casing has, in addition, a layer of peeling agent on the inner side of the casing, which may influence the growth of the molds.

Collagen Casings

(filled manually or automatically with filling horn)

Less growth potential for molds then on natural casings but better than cellulose casings. Collagen casings have a good evaporation capacity hence they influence the growth of molds positively.

Collagen Casing

(Co-extrusion system in continuous formation of sausage and casing simultaneously)

The application of the molds may have to be postponed to after the formation of the casing layer and after the initial fermentation and drying period.

In some cases, the use of molds may be difficult because the time span is too short.

Natural Casings

Natural casings come in a great variety and shape and type (sheep, horse, pig, etc). The degree of preparation is highly variable and the micro-biological quality is not always excellent.

Natural casings should be well prepared (cleaned and soaked) prior to use. Natural casings are ideal for molds and very often give densely covered sausages.

It may be necessary to be more restrictive with the fermentation scheme in order to limit growth of molds.

Fermentation technology

Successful mold application depends on good regulation of relative humidity, which is responsible both for good growth as well as for the inactivation of the molds.

In addition, it requires fine-tuning of airspeed and temperature control.

In general:

  • Ideal growth takes place at a relative humidity of > 90 %.
  • Airspeed should be very moderate to moderate.
  • Temperature should be between 24–30°C


The difference in relative humidity (r.H.) between the sausages and the air used in dry fermented sausage production can vary a lot depending on technology and local customs.

It is important to note that a small change can have a big influence on the outcome; e.g. when the difference in r.H. between the sausage and the air is too big the evaporation/flow of humidity becomes discontinuous and this leads to a dry rim.

Trial observations have shown that r.H. 4% below optimal conditions delayed the full development of the white cover by 6 to 8 days when artificial cellulose casings were used.

In addition, non-optimal growth conditions lead to higher infestation by wild contaminants and enhance dry rim characteristics.


Good sporulation temperatures are above 24 °C. Lower temperatures slow down growth, very low temperatures impede sporulation.

Temperatures should not exceed 30°C.

Airspeed and fresh air control

Airspeed should be low at the beginning (0.1 to 0.2 m/s) and high-speed air ventilation should not exceed 0.6 m/s to avoid extreme turbulence, which can make the hanging sausages swing.

High airspeed is mainly used on purpose to give a “crust” to the sausage and to slow down the drying speed.

When applied too early, high airspeed will lead to a dry rim often with negative consequences.

Most fermentation equipment relies on combined regulation, i.e. the equipment uses recycling of air and introduction of fresh air in order to obtain the required condition.

This means that there may be a source of contamination of the sausages by negative flora like rhizopus or mucor etc. from the fresh air. Microfilter systems can avoid these unwanted contaminations by way of purification of the incoming air.

The filters should be cleaned and sterilized from time to time in the same way as the fermentation equipment; special care should be attributed to the cleaning of the ducts and the area around the condensation unit.

Source: Chr.Hansen


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