The moisture content of parchment coffee can be measured with handheld machines that can be taken to the drying beds each day. However, these machines are not common on most coffee farms because they are very expensive. Dehydration ovens can also be used for this purpose, but these are even more prohibitively expensive. Farmers have developed other metrics to estimate when their coffees are dried to a safe level. A common system is the ‘tooth test’ where a miller will literally bite into a bean. If it's chewy or the tooth leaves an impression, the coffee is insufficiently dry. However, research by the International Coffee Organisation (ICO) suggests this method is not consistent for differentiating between coffees with moisture levels between 12–20%. Instead, the ICO recommends the following cheap method for measuring moisture, involving cooking oil.