Posted by Eric Troy on 15 Nov 2012 19:45
According to many food preservation books, as well as cookbooks and magazine articles, yes, apples, when stored with potatoes, will help prevent early sprouting. This information, however, comes from experiments carried out in the 1930's and reported for many years in related articles and books. Current scientific sources would suggest the opposite update: I was wrong. That is, if apples are stored in close proximity to potatoes, they will cause potatoes to sprout prematurely.
Apples, as part of the ripening process, give off ethylene gas, and this gas promotes the sprouting of the spuds, whereas, early on, it was claimed that ethylene gas prevented sprouting. Potatoes, as well, will cause the apples to get mushy and moldy more quickly.
Ethylene is a colorless, odorless, and tasteless gas which acts as a plant hormone, having many physiological effects, most of which are related to growth regulation. This gas has such profound influence that it can effect stored fruits and vegetables at levels of only one part per million. It induces rapid ripening and softening of many fruits like apples, bananas, avocados, tomatoes, kiwi, mangoes, etc. Ethylene also causes many vegetables, like spinach, broccoli, cucumbers and celery, to yellow. Also, in a process called abscission, cabbage and broccoli will drop leaves.
Iceberg lettuce may develop small brown spots called russet spotting in the midribs due to exposure to the gas, and ethylene is also responsible for a bitter taste in carrots due to the formation of isocoumarins and other phenolic compounds. As well, ethylene causes asparagus to become tough.
Good ventilation and the presence of CO2 can retard these effects, presumably because it competes with ethylene for binding sites. Therefore, it has been shown that the activity of ethylene can be abolished by the presence of 10% Co2. This is great for food science, but not very useful for you and me.
Ethylene can be generated inexpensively by readily available ethylene generators, such as ethephon. It is used commercially to promote the uniform ripening of fruits, such as pineapples and tomatoes. Since bananas are harvested and shipped green, ethylene treatment can be used to quickly ripen them once they arrive at destination, and for many other purposes.
The take-home is that ethylene gas tends to cause changes to occur in fruits and vegetables, often profound changes. The idea that ethylene gas, which is the only possible way that apples could affect potatoes, would cause the potatoes to stay the same, is a bit absurd. Ethylene may cause several changes to occur in a potato, but one of the main ones seems to be to cause sprouting. update: See why I was wrong
Does all of this mean you have to keep apples in a separate room from potatoes? Not really. Nor does it mean that if you have a root cellar you must keep the apples segregated. As long as there is good ventilation you won't have a problem. But if you shut up the apples and potatoes in a bag, even a paper one, your potatoes won't last. Same with any other enclosed container.
If ethylene doesn't retard the sprouting of potatoes, does anything? Yes. I've already mentioned CO2 gas, for example. Irradiation can also inhibit sprouting in potatoes, onions, carrots, garlic, and ginger. The chemical maleic hydrazide also inhibits sprouting in potatoes, onions, and other root crops. In fact, there are many methods of controlling the fate of fruits and vegetables postharvest. Each of them has advantages and drawbacks. For more reading consult Postharvest Technology of Fruits and Vegetables: Handling, Processing, Fermentation and Waste Management, by L. R. Verma and Dr. V. K. Joshi.7
First, do not store potatoes in the refrigerator. This causes the starch to be converted to glucose and a waxy consistency when cooked. Except for new potatoes, which never last long, potatoes will keep longest in a cool (45-50 F), dry, and DARK place. A paper bag with the top rolled down will work well, and you probably do not need to cut holes, as paper bags breathe a bit. There are commercially available canvas or burlap bags that are made to store potatoes and other root vegetables, but they probably will not provide any advantages over a simple paper bag. You can also store them in a basket away from light. If you don't have a cool, dark place, just store them away from light at room temperature. Do not place potatoes directly on a concrete floor.
Upon gathering further research, it seems my sources, and I, were dead wrong on this question of ethylene's effects on potato sprouting. Now, the current best method in the industry for preventing potato sprouting does not seem to be ethylene gas. I'll get to why that is in a moment.
The primary study I've found evaluating the effect of ethylene on tuber sprout growth in potatoes us quite an old one, published in the Journal of the American Society for Horticultural Science, 'Using Ethylene as a Sprout Control Agent in Stored ‘Russet Burbank’ Potatoes.' 8.
In the study, which consisted of 6 years of laboratory studies and 3 years of commercial studies, potatoes were either untreated, treated with the industry standard CPIC (which by EPA mandate is limited), and ethylene gas. Ethylene was applied continuously at 166 μmol·m-3 for at least 25 weeks. In the laboratory studies, the ethylene delayed the appearance of sprouts for 5 to 15 weeks. When sprouts did occur, they appeared on many eyes, but most of them were very small. Longer eyes appeared after 15 weeks, but were more easily removed than usual, up to 6 weeks after the ethylene treatment ended. There were no problems with the potatoes in terms of decay or internal sprouting. However, the ethylene-treated potatoes had a darker Agtron fry color than CIPC-treated potatoes.
The Agtron fry color is measurement of the fry color of strips of fried potato, referenced to a USDA chart. The industry standard is a light "golden-brown." In order to achieve this, sugar concentration in the potatoes much be controlled. Ethylene gas is not the only determinant, but too much ethylene in the atmosphere causes potatoes to brown more quickly.
Another study, in the American Journal of Potato Research, 'Sprout development and processing quality changes in potato tubers stored under ethylene: 1. Effects of ethylene concentration' 9, attempted to determine if altering the concentration of ethylene during storage could reduce darkening but still effectively inhibit sprouting. There was little success, and at concentrations high enough to inhibit sprouting, the fry color was still darker than with CPIC. Ethylene is not the preferred industry method for inhibiting sprouting, due to these changes.
Although these experiments, and any commercial treatment, use very precise concentrations of ethylene in a controlled air-exchanged environment, if you expose potatoes to more ethylene, it certainly should inhibit sprouting. So, storing your potatoes with an apple can be expected to work. I didn't want to mention informal experiments, but on commenter brought up the experiment by America's Test Kitchen, which found that storing a 5lbs bag of potatoes with an apple delayed sprouting for 8 weeks (according to online articles about the episode). Since this confirms the evidence from the studies, I include it here. So, yes, storing potatoes with an apple should keep them from sprouting for much longer. If you fry them up, expect that they may be difficult turn too dark.
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