Water activity in meat

Meat preservation has been used by civilizations for thou­sands of years to provide a long-term protein source that won’t spoil during storage or travel. The preservation of meat through curing dates to antiquity, often discovered through accidental mis-handling of meat. The most com­mon methods used to cure meat include salting, brining, smoking, and drying. All these preservation methods rely on the control of water activity. In fact, the legacy of Shelf stable meats and water activity go hand in hand. Ancient civilizations did not have an exhaustive unders­tanding of water activity or why these preservation steps worked, but instead discovered them through trial and error. In so doing, they discovered the fundamental truth that still alludes many processors today, that its water acti­vity, not moisture content that makes cured meats shelf stable.

Water activity in meat and microbial safety

There is an ideal internal water activity for every microorganism, they need to maintain that water activity to reproduce and grow. These growth limits indicate that all pathogenic bacteria stop growing at water activities less than 0.87 while the growth of common spoilage ye­asts and molds stops at 0.70 a_w, which is known as the practical limit. Other intrinsic factors such as pH impact microbial growth as well. For a shelf stable meat product to be considered non-potentially hazardous, its water activity must be less than 0.86 a_w or its pH less than 4.2 to ensure that no pathogenic bacteria will be able to grow on the product as it sits on the shelf.

Shelf stable meat with a water activity higher than 0.70 a_w but less than 0.86 a_w is consi­dered shelf stable but will still support the growth of mold and yeast. Consequently, the water activi­ty must be reduced to below 0.70 a_w or other interventions such as a pre­servative system or vacuum packing must be used to prevent mold growth.

Water Activity in Meat and stability

The water activity of intermediate mo­isture and dry shelf stable meat will typically be less than 0.70 a_w, indicating that mi­crobial growth is not likely to occur. However, shelf stable meats in this range do not have unlimited shelf life. So what ot­her modes of failure are likely to occur to end shelf life. For meat products with a pH Measurement and water activity in the 0.40-0.70 a_w range, lipid oxidation, which leads to the off odors and flavors as­sociated with rancidity is a strong candidate because re­actions rates are at a maximum.

A particular mouthfeel and texture are associated with each type of shelf stable meat and are undesirable to the consumer when they do not meet these desired physical characteristics. Products that are expected to have a stiffer texture need to be at a lower water activity while those that are expected to be soft need to be at a higher water activity. If either type is processed to the wrong water activity, they will not have the desired characteristics and will be rejected by the consumer.

The most important specification: water activity in meat products

For shelf stable meat, setting an ideal water activity specification is a critical step in formulating for safety and quality. The specification can be set to avoid microbial proliferation, minimize chemical reactions, and provide the desired textural properties. The ideal value can be determined based on the most likely mode of failure, such as texture change for low water activity shelf stable meat, chemical degradation for semi-moist shelf stable meat, and microbial growth for moist shelf stable meat. Once the ideal water activity is determined, a combination of processing and formulation can be used to achieve that ideal water activity while maximizing revenue by avoiding unnecessary overdrying.