Time temperature indicator

A time temperature indicator (TTI) is a device or smart label that shows the accumulated time-temperature history of a product. Time temperature indicators are commonly used on food, pharmaceutical, and medical products to indicate exposure to excessive temperature (and time at temperature).

In contrast, a temperature data logger measures and records the temperatures for a specified time period. The digital data can be downloaded and analyzed.

By timespan
The basic types of time-temperature indicators include:
 * Partial history indicators: These are time-temperature indicators that provide a visual indication of whether a product has been exposed to temperatures outside the recommended range during a specific portion of its life cycle.
 * Full history indicators: Unlike partial history indicators, these give an indication of whether the product has been exposed to temperatures outside the recommended range during the entire life cycle.
 * Critical temperature indicators: These monitor a critical temperature threshold that, if exceeded, may cause irreversible damage to the product.

Digital temperature data loggers are available to indicate the full temperature history of a shipment to help identify the time period that out-of-tolerance temperatures were encountered. This temperature history can be used to calculate the loss of shelf life or the likelihood of spoilage. These small recorders are also used to identify the time (and thus location) of a shipment when the problem occurred, which allows for corrective action.

By technology
There are a large number of different time temperature indicators available in the market, based on different technologies. To the degree that these physical changes in the indicator match the degradation rate of the food, the indicator can help indicate probable food degradation.
 * Enzyme-based TTIs: an enzyme changes the color of the dye on a piece of filter paper as time passes
 * Microbe-based TTIs: a mixture containing dye and bacteria changes color as bacteria grow and chemically changes the dye
 * Digital TTIs: a miniature temperature data logger can be attached to the item. RFID communication can be used to retrieve the temperature log.

TTIs in the food industry
Time-temperature indicators can be used on food products that are dependent on a controlled temperature environment. Certain technologies can also be used for frozen food and the cold chain.

Meals, Ready-to-Eat (MREs) from the US military have included "Fresh-Check" TTIs on the cardboard boxes since 1997 to help estimate their shelf lives.

Benefits
Surveys within the European Union projects "Freshlabel" and "Chill-on" have shown positive feedback from consumers on the use of TTIs on food products. As TTIs help assure the cold chain of food products, they are expected to reduce the amount of food waste, as well as reducing the number of foodborne illnesses.

Regulation
The World Health Organization regulates the use of TTIs for certain medical products. There is extensive regulation by the FDA on the use of TTIs on US seafood products.

General References

 * ASTM F1416 Standard Guide for Selection of Time-Temperature Indicators
 * Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6
 * Taoukis, P. and T.P. Labuza. 2003. Time temperature indicators. In: Novel Food Packaging Techniques. R. Ahvenainen (ed.). Woodhead Publ., Cambridge, UK.