Hay steaming is a method of treating hay to reduce the airborne respirable dust which naturally occurs in hay, causing respiratory problems in both humans and horses when in close contact. The method encompasses a steam generator which produces the steam and a connecting hose to direct the steam into a closed, sealed vessel containing the hay, exposing it to the steam. Importance of temperature When a professionally engineered and designed high temperature steaming method is used, the temperature of the hay reaches over 100 °C. This has been scientifically proven to kill the bacteria, mould and fungal spores thereby improving the hygienic quality of hay and dramatically reducing airborne respirable dust by up to 98%. With hay steaming, however, if the required high temperatures are not reached it can have a detrimental effect on the hygiene quality of the hay by creating an “incubator effect”, leading to a dramatic increase in observed bacteria. Expectation is that only hay steamers which are able to steam from the inside out (specifically injecting steam via spikes from deep within the hay, rather than from the outside in, releasing the steam from underneath the hay) and with the hay being steamed while placed in an insulated vessel, are able to reach the requisite temperatures to avoid dramatically increasing bacteria. This may, however, create effluent runoff with very high bacterial levels. Some designs have demonstrated effective reduction of bacteria in the hay and effluent runoff by 99+% without the need for spikes. Home made versions A number of homemade hay steamers have been tested, usually consisting of a “wheelie-bin” and a “wall paper stripper,” and all failed to reach the needed temperatures to avoid the incubator effect. There are no published studies linking this effect to any specific ill effects in horses, though it is generally agreed to be undesirable. Importantly, studies have shown homemade hay steamers to have some beneficial effect in reducing dust and mould spores and, when normally acceptable n-values are used to process the results data, the difference is material but not extreme. Soaking versus steaming Before hay steamers were invented, horse owners would soak hay in a bucket or tub of water for anything from 10 minutes to 12 hours and then drain it. A 10-minute soak has been shown to reduce respirable dust by up to 90%. This method uses water to dampen down the dust so it