Compost tea, generally defined as a liquid extract of compost, has gained acceptance by homeowners and commercial growers around the world for its ability to stimulate soil biological activity, improve soil structure, and enhance overall plant health and vigor. Reported benefits of using compost tea include enhanced disease suppression, reduced fungicide and fertilizer requirements and associated cost savings. Research efforts to validate these benefits are expanding. The contemporary compost tea industry by and large uses the term "compost tea" in reference to an aerated extraction process. Historically, the term "compost extract" (among others) was used to describe an extraction process that may or may not include active aeration. Until very recently, almost all published research on the benefits of compost extracts pertained to non-aerated processes. The first known commercially available industrial-grade, aerated compost tea system was introduced in the United States in 1997. There are now several compost tea systems on the market with a range of features and capacities, reflecting growing demand for these systems and the inception of a new industry.

Aerated compost tea systems are designed to consistently provide optimum conditions for extraction and proliferation of beneficial aerobic microorganisms present in the starting compost, as well as extraction of the components from the compost that are either soluble or able to be held in suspension. In almost all compost tea production scenarios, compost or vermicompost is the source of organic matter, organisms and nutrients for extraction. The resulting tea is therefore directly influenced by the characteristics of the starting compost.

Though designs vary, most commercial aerated tea systems consist of a tank, a mesh container/filter for holding compost, and an aeration system. The ratio of compost to water varies with the system, but in one example approximately 5-7 pounds of compost is used in 25 gallons of water to make a concentrated product that can then be further diluted depending on the application. The typical extraction period for aerated compost tea is 24 hours. Most commercial tea production includes the addition of supplemental microbial food sources to enhance microbial growth and diversity. Research and experimentation are ongoing among compost tea users to assess the effects of these supplemental foods.

Compost tea has many of the same beneficial attributes of compost, but it is clearly a different product. Unlike compost, it can be applied directly to plant foliage, providing nutrition and beneficial microorganisms that colonize leaf surfaces. This is thought to be instrumental in the disease suppression capabilities of compost tea. Compost tea applied directly to the soil is a way to boost biological activity when application of solid compost is not practical, or as a supplement between compost applications.

Because it is a relatively new industry, the body of knowledge on aerated compost tea systems is not expansive. Enthusiastic feedback from users indicates a strong demand for more scientific information and practical guidance. As in compost production, there are a number of variables that influence the ability to make a consistent batch of compost tea. Aerated compost tea system manufacturers have made progress in controlling critical mechanical variables such as aeration, extraction, mixing, temperature, cleaning and scheduled maintenance. Further progress is needed to effectively manage the remaining variables, to identify specific biological mechanisms responsible for the beneficial effects of compost tea, and to identify appropriate application strategies in specific cropping systems.