recent units generally have a more traditional-appearing horizontal pan. Some bread machines use the standard rectangle shape using two paddles. One Zojirushi model has a heating element in the lid to brown the crust. Bread machine recipes are often somewhat smaller than standard bread recipes, and are sometimes standardized based on the capacity of the machine's pan; most common in the United States market are 1.5 lb/700g units, and the majority of recipes are written for that capacity; however, 2 lb/900g units are not uncommon. Packaged bread mixes are available, specifically designed for breadmakers, containing premeasured ingredients including flour and yeast, as well as flavorings and occasionally dough conditioners. Only water usually needs to be added. Bread machines generally do not deal well with non-wheat flours, so any recipe that requires a substantial addition of a grain such as rye or corn that lacks gluten will prove difficult at best in a bread machine, as will any dough with unusually large amounts of liquid (such as ciabatta). Generally, homemade bread goes stale faster than bread from a commercial baker because the former does not include preservatives. However, it is possible (though a bit more difficult) to use a natural leaven or a pre-ferment in breadmaker dough recipes if the starter is sufficiently fast to rise. Sourdough contains a symbiotic culture of yeast and lactobacteria; the yeast provides some flavor as well as carbon dioxide to provide lift, while lactic acid produced by sourdough's lactobacteria greatly preserves bread, as well as affecting its flavor, while pre-ferments provide some of the same benefits as a sourdough culture with the greater predictability of domesticated baker's yeast. Breadmakers are often equipped with a timer to control when the breadmaking begins. This allows them, for example, to be loaded in the evening but only begin baking early in the morning, to produce a freshly baked loaf for breakfast. They can also be set only to make dough, for instance to be used to make pizza. Some can also be set to make other things besides bread, such as jam, pasta dough, udon or mochi, a kind of Japanese rice cake. One of the most recent innovations is the facility to add nuts and fruit during the kneading process automatically from a tray. Traditionally, breadmakers take between three and four hours to bake a loaf. However recently "fast bake" modes have become common additions, many of