Water Activity in Meat
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 aw, 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 aw 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 aw but less than 0.86 aw 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 aw 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 aw, 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 aw 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
"The careful monitoring of the water activity of shelf stable meat during production can reduce energy inputs and prevent undesirable weight loss due to processing to lower than ideal water activities. This will reduce ener¬gy waste while maximizing revenue. In summary, establishing an ideal water activity specification, formu¬lating to meet that specification, and monitoring production with frequent water activity testing will ensure a safe, quality product with an optimal shelf life and maximum revenue. In short, the success of shelf stable meat throughout history is directly tied to a legacy of water activity control."
Dr. Brady Carter World-renowned specialist in water activity.