Improving dry sausage quality by controlling temperature and humidity

By Joseph Sebranek Ph.D on 2/1/2009
MeatingPlace.com

In this article:
Temperature considerations
Humidity considerations


The manufacture of dry sausage is probably the oldest form of meat preservation. Dry sausage was undoubtedly discovered by accident and gradually evolved into a popular means of preserving meat in a highly palatable form.

In fact, the development of dry sausage varieties can be traced to geographical areas where natural climatic conditions offered an environment in which temperature, humidity and other factors resulted in a product with distinguishing characteristics. Northern Italy, Hungary and Switzerland are some of the areas in Europe, for example, where dry sausage products have evolved over time to the point of becoming distinct products that are recognized all over the world. Pepperoni, Genoa salami and cervelat are some typical products from this region that are widely recognized. Other parts of the world have produced dry sausage varieties that resulted from environmental and cultural conditions characteristic of those localities.

Production of dry sausage clearly was a poorly understood but well-perfected art form for centuries. It has only been in the past 50 years or so that the physical and chemical changes that occur during dry sausage production have been studied and explained to permit improved control of the process.

While many factors including raw meat quality, salt, cure and pH are critical considerations for dry sausage quality, the very nature of "dry" sausage means that temperature and humidity will be critical during key steps of the process.


Temperature considerations
Temperature considerations for dry sausage are usually focused on temperatures used for the drying process, but it's important to realize that temperature effects on product quality actually begin with the raw meat used for product formulation. Meat must be kept very cold during grinding, mixing and/or chopping to avoid fat smearing, which can form a film of fat over the lean tissue and reduce the movement of water out of the product. Meat should be maintained at -2 degrees C to -4 degrees C (24 degrees F to 28 degrees F) to facilitate good fat/lean distinction and allow effective moisture migration.

Frozen meat is often used as part of the formulation to achieve temperature control. Use good quality frozen meat, because another temperature/quality issue can arise. Frozen meat stored at higher than ideal temperatures (above -20 degrees C/0 degrees F) is likely to develop rancid flavors that will subsequently be magnified by the drying process.

Avoiding fat smearing during stuffing is also important, particularly because a film of fat just under the casing can dramatically slow the migration of water out of the product. So, again, temperature becomes an important consideration and should not exceed -1 degrees C to 0 degrees C (30 degrees F to 32 degrees F) during stuffing. Using large-diameter, short-length stuffing horns can also minimize fat smearing in dry sausage.

Following stuffing, most dry sausage will be fermented, either in a "green room" or a fermentation chamber. Because most traditional dry sausage types are fermented with cultures that do best at relatively low fermentation temperature, a temperature of 22 degrees C to 24 degrees C (72 degrees F to 75 degrees F) is typical. Determining the best fermentation temperature for the culture used is important to producing the desired pH within the targeted time for achieving optimal product quality and safety. Relative humidity becomes important at this point, with 95 percent recommended to facilitate growth of the culture and active production of lactic acid.

Following the fermentation step is drying, which is the most critical step in the production of dry sausage and where temperature (and humidity) will have a major impact on final product quality. To be successful, the drying process must achieve surface evaporation at very nearly the same rate as moisture moves through the product to the surface.

It should be no surprise that the rate of migration within a product will vary with product diameter, pH and texture of the mixture. If drying is too fast, a crust forms on the outside of the product (case-hardening), and additional water removal becomes difficult and slow. This can also contribute to the problem of pepperoni slices "cupping" on pizzas when cooked. If drying is too slow, surface growth of mold and other microorganisms is likely to occur.

Successful drying requires control of conditions within a relatively narrow set of limits for temperature, relative humidity and air-flow rates. Recommended temperature in drying rooms is generally in the range of 10 degrees C to 13 degrees C (50 degrees F to 55 degrees F).

However, the temperature becomes an interactive factor with relative humidity and air flow at this point, and conditions need to be fine-tuned in a given drying facility to achieve the best performance. Air flow must be relatively slow to maintain uniform temperature and humidity, yet uniformity is difficult to achieve with slow air speed, especially in large drying rooms. The air contact with product surfaces will pick up moisture, meaning that relative humidity of the air is changing as the air moves through drying rooms. In large rooms, this means that uniformity is increasingly difficult. Air speeds of 0.15 ft/sec to 0.3 ft/sec (0.05 m/sec to 0.1 m/sec), or about 15 to 25 air changes per hour, are good starting points.


Humidity considerations
Relative humidity first becomes a consideration for fermentation when at least 90 percent is recommended and 95 percent or more is often used. For drying, however, the relative humidity must be reduced to achieve evaporation of water from the product surface. A relative humidity of 72 percent to 75 percent is recommended by many dry sausage experts. This level is usually sufficient to prevent surface mold growth while avoiding case-hardening.

For those products in which surface mold is desired, a higher relative humidity at the beginning of the drying process is necessary. The relative humidity may also be slowly decreased from just below 90 percent to 65 percent or 70 percent as drying progresses, if drying room control is sufficient to achieve these conditions.

As a general rule, the drying rate should not exceed about 1 percent per day during the early phases of green room curing and fermentation, and should not be more than 0.7 percent per day during drying. However, keep in mind that when it comes to dry sausage, every drying process should be fine-tuned for each product and drying environment that is used in order to maximize product quality.

Using pre-rigor meat to improve sausage yield and texture

By Joseph Sebranek Ph.D on 2/1/2009
MeatingPlace.com

In this article:
What is pre-rigor meat?
Handling and preparation
Advantages of pre-rigor meat in sausage

One of the most fragile and variable properties of meat as a raw material for sausage products is the ability of meat to bind and retain water during and after processing and packaging. Drip losses, low product yields and package purge are all common problems that result from poor water-binding.

Because the retention of water is critical to texture, mouthfeel and juiciness, water-binding problems during processing carry over to consumer-perceived product quality. Further, because water-binding is a meat property that is sensitive to changes in processing procedures, it often serves as a warning indicator for other product changes. For example, in emulsified products such as frankfurters, water-binding ability is one of the first changes to occur when the emulsion is becoming less stable. This means that a decrease in yields may be a warning that the emulsion is close to breaking down with release of fat as well as water if corrective action is not taken.

Lean meat has an inherent water content of about 70 percent, and water is often added during formulation. Consequently, retaining both inherent and added water in sausage is a significant challenge. One of the most effective ways to meet this challenge is with the use of pre-rigor meat. Pre-rigor meat offers some tremendous advantages over post-rigor meat for sausage and processed products, but must be handled correctly to realize those advantages.


What is pre-rigor meat?
Simply stated, pre-rigor meat is meat that has been "hot-boned," or removed from the carcass prior to chilling and before development of rigor mortis. Pre-rigor meat is characterized by a pH well over 6.0 — usually in the range of 6.4 to 7.0 — and a high degree of protein solubility.

The muscles of live animals have a normal pH of just over 7.0, but biochemical changes in muscles that begin immediately postmortem will generate lactic acid, which in turn will change the meat pH to about 5.2 to 5.6 over a period of several hours. The reduced pH is typical of post-rigor meat and means that the proteins in the meat now have a weaker molecular attraction for water molecules.

At the same time, the reduced pH stimulates irreversible muscle contraction. Contraction or rigor mortis results in less structural space between muscle protein filaments as the muscle attempts to shorten. This physical effect reduces the space within the muscle that is available for water.

The combined effect of a weaker molecular attraction for water as well as less space for water means that post-rigor meat has considerably less ability to hold water than does pre-rigor meat. The key to retaining the advantages of pre-rigor meat is to minimize the pH change and the muscle shortening that normally occur as postmortem muscle develops rigor mortis.


Handling and preparation
To fully realize the advantages of pre-rigor meat, it is critical to remove the meat from the carcass as soon as possible following slaughter. However, this process introduces three potential problems.

First, intact muscles removed from the carcass will contract and shorten excessively if allowed to go into rigor, greatly reducing the space available within the muscle structure for water binding. This problem is easily overcome by coarse-grinding the meat immediately to break up the muscle contractile structure.

Grinding introduces a second potential problem in that the biochemical changes in muscle that produce lactic acid are accelerated by grinding. It is critical at this point to blend the meat mixture with salt, because salt disrupts the acid-producing enzymes and virtually stops the production of acid to prevent further decline in meat pH. It is important to add salt as soon as possible in order to retain the meat pH at the highest possible value.

Salting pre-rigor meat has additional advantages of solubilizing salt-soluble proteins to a greater extent than in post-rigor meat. This results in a firmer texture in cooked products and more effective stabilization of fat in emulsified products.

The salt concentration used may be in the range of 1.5 percent to 4 percent, depending on the salt concentration desired in the product in which the pre-rigor meat is to be used. The salting step is also the appropriate time to add nitrite if the pre-rigor meat is intended for use in a cured product, making the mixture similar to a pre-blend but with the advantages of pre-rigor meat. Typically, one-half of the final product nitrite concentration is used in pre-blends.

The third potential problem that can arise in handling pre-rigor meat is rapid bacterial growth in the warm, coarsely ground mixture. Rapid chilling such as with carbon dioxide snow in a mixer/blender becomes an important step. Rapid chilling also helps to slow the production of lactic acid, and when combined with salting will virtually stop the change in pH. If the pre-rigor meat is to be used for an uncured product such as pork sausage, it may be of value to chill prior to or with the addition of salt to minimize the effects of salt on fresh meat color.

Thus, to maximize the advantages of pre-rigor meat, deboning must be done as quickly as possible, followed immediately by coarse-grinding, blending with salt (and nitrite if appropriate) and chilling as rapidly as possible to 28 degrees F to 30 degrees F.


Advantages of pre-rigor meat in sausage
With proper preparation, use of pre-rigor meat brings several advantages to sausage products. Cooked product yields can be dramatically improved, with increases of 4 percent to 10 percent reported in research literature. Both fat and moisture retention are improved, resulting in improved palatability. Product texture also is modified due to greater protein extraction, with firmer texture resulting from pre-rigor meat.

In the case of cured products, the pre-cured, pre-blended mixture provides superior binding for emulsions and improved cured color. In the case of fresh uncured sausage, pre-rigor meat provides a brighter fresh meat color and longer color life in a product that is typically very color-sensitive.

Finally, the rapid chilling and early addition of salt keeps bacterial numbers low and results in longer product shelf life in terms of bacterial spoilage. Consequently, there is little not to like about using pre-rigor meat for sausage products.

Tips to optimize your grinding operation

Tips to optimize your grinding operation
By Ana Elia Rocha McGuire on 7/1/2008

Particle reduction is the basic technology for producing many meat products. During the process of grinding meat, many factors affect quality and must be controlled. These factors include the quality of raw materials, temperature during processing and equipment maintenance.

Although it won't be covered in this article, it's important to remember that good practices, hygiene and sanitation are extremely important during the production of ground products, and should always be executed and monitored.


Use high-quality raw materials.
To obtain a good product, it is necessary to use high (or acceptable)-quality meat, fresh and cold, with high water-retention capacity. Hamburgers made with Utility-grade pieces (the lowest-quality meat according to USDA) were less accepted by consumers than those made with Choice quality meat from the chest. Avoid using meat with a pH under 5.5 and a pale or discolored appearance.

Although not always practical in today's grinding operations, pre-rigor meats are considered excellent for yielding high-quality finished products, and should be an option.

Since it is softer than muscle, fat content in the meat can affect the efficiency of bone-removal systems in the grinders. The source of fat must also be considered. Pork fat is softer than beef fat at the same temperature because they have different degrees of unsaturation. So, when pressure is developed during grinding, pork products are more susceptible to smearing. To avoid this, pork grinding should be handled at slightly lower temperatures than beef grinding. One study suggested that a different bone-removal system design might be better for beef as opposed to pork products, and for high-fat as opposed to low-fat mixtures.

Other factors that affect product quality are the amount of bone chips, cartilage and connective tissue, too much of which may result in consumer rejection.


Keep a low temperature during grinding.
Temperature is always a control measurement in meat processing, both from a qualitative and microbiological standpoint. Given that, it is critical to try to use meat at a temperature of 28 degrees F or lower. Usually the temperature of the system rises a couple of degrees after grinding, making the meat more prone to microbial proliferation, but if you start with very cold meat, you should be fine.

Also, meat temperature affects equipment performance during grinding. A study investigated the effect of meat temperature, particle size and grinding systems on removal of bone chips from ground beef. It was observed that cold grinding temperatures (28 degrees F) resulted in a higher percentage of bone chips removed by the bone-removal system compared to higher grinding temperatures (38 degrees F).


Maintain equipment in good condition.
Since grinding meat results in more exposed surface, those meat components prone to oxidation — fat and myoglobin, for example — are then more susceptible to changes, because they are exposed to oxygen and catalysts. As grinder parts wear with use, the equipment shears less and smears more, increasing the exposed surface area of the meat even more. Increased friction raises the processing temperature of fat and myoglobin, promoting an even greater level of oxidation.

In a study of the effects of meat grinder wear on oxidation in fresh pork sausages, worn grinder hardware caused greater myoglobin oxidation in the sausages after frozen storage than sharp hardware. Worn hardware also caused greater grinding temperature increases than sharp equipment.

Therefore, equipment blades and plates must be perfectly sharpened and kept in good condition. Keeping grinder blades sharp will maintain a high-quality grind. This will allow proper contact between knife and plate across the cutting surface.

It is important to note that a new or newly sharpened part should never be put with another part that is worn. Mismatched sets will result in premature failure of both parts.