There are a few different methods you can use to ripen an avocado, depending on how quickly you need the fruit to be ready to eat. Since avocados do not ripen on their trees, the selections available in grocery stores are often still hard, green, and several days away from being ripe enough. Of course all avocados will eventually ripen over time, but if you need to ripen an avocado quickly the process can be expedited by manipulating the fruit’s natural ripening signals using ethylene gas.
If you bring an avocado home from the store and it is very hard, you can simply leave it out on a table or countertop until the flesh becomes soft and ripe. This may take several days, so if you are planning to serve a recipe that requires ripe avocados on a certain date, it may be wise to plan ahead and purchase the fruit in advance to allow ample ripening time. The refrigerator is not a good place to ripen an avocado because the cold temperatures will slow the ripening process.
Ripening an avocado more quickly will also require some wait time, but not as much as leaving it to its own devices out in open air. When fruit ripens, it releases ethylene gas in what is sometimes referred to as a ripening signal — the ethylene gas cues ripening processes to begin. An avocado sitting on a countertop by itself will release ethylene gas, but it will be diffused by the air around it; the ripening process will occur, but not particularly quickly. Using a paper bag is a faster way to ripen an avocado because the ethylene gas gets trapped inside and hastens natural ripening processes.
Wrapping an avocado is a good way to manipulate the ripening to happen faster, but the process can be taken even further with a few simple alterations. If you are attempting to ripen more than one avocado, place them all in the same bag. Logically, the more avocados that are in the bag, the more ethylene is being released, and the avocados are likely to ripen faster. Similarly, you can also ripen an avocado by placing an already ripe fruit such as an apple or tomato in the bag along with the avocado to increase the amount of ethylene and therefore hasten ripening. Bananas are commonly believed to be the best fruits to use in aiding other fruits to ripen because they produce greater quantities of ethylene gas.
Paper bag packages such as these can be left out at room temperature, or may also benefit from being placed in the oven so long as the heat is turned off completely and the internal light is on. Do not turn the oven on because not only could the bag catch fire, but it will not help the avocado ripen anyway. The oven light alone will provide a very gentle amount of heat that may help speed ripening.