Chilly Food: Is Moldy Margarine Dangerous to Eat?

Written and curated by FridgeMaster William Jackson

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moldy margarine in closeup - do not eat

Differences between Butter and Margarine

I don't know anyone who doesn't like a slice or two of freshly toasted bread, or freshly baked rolls, with some butter spread on it. Of course, healthy eating demands less fat - meaning less butter. Margarine is a popular substitute for butter, with a similarly pleasant taste. If margarine is a more healthy food than butter, what are their differences? Also, does margarine stay fresh as long as butter? Is mold a risk if margarine is not refrigerated?

Butter and margarine are both fats. Butter is derived from milk, while margarine is derived from plant based fatty oils. Butter and margarine are more unfavorable for bacterial growth than other foods, as they contain lots of fat, but a low percentage of free water. Life is robust, though, and there are a few bacteria and mold which can live in them. See our other article, Risks of Moldy Butter for more about butter. Here, we will continue our focus on the freshness and safety of margarine.

Margarine Will Go Rancid
Molds on Butter
Margarine Storage Suggestions

Margarine Will Go Rancid

Margarine's plant based fatty oils help to stay fresh for a time about one third longer than butter. The main freshness issue with margarine is that its fats will eventually oxidize, breaking down into acids. It happens faster when margarine is kept at room temperature or exposed to sunlight or warm weather. Rancid margarine has an unpleasant smell and taste. Not only is rancid margarine unpleasant, but it is a more favorable environment for harmful bacteria to grow.

Rancid margarine poses an additional risk, besides bacteria: free radicals. Free radicals are corrosive molecules which are believed to cause cancer and accelerated aging in mammals. When you hear nutrition and health experts speak of the value of antioxidants, their value is in neutralizing those free radicals.

Molds on Margarine

The organisms we refer to as "molds" are fungi - not very different from edible mushrooms and fungi used in salads or on a steak, but much smaller. Molds are microscopic. They need oxygen, moisture, and organic matter to live.

Margarine is high in fat, but low in water content, and does not contain much organic matter favorable to molds. Molds which do grow on margarine are fairly limited. The three common types of mold found to live on margarine are:

Do not try to salvage margarine which has gone bad. If the margarine is rancid, or if you see areas of green, black, or grey mold on it, discard the whole container. You can't tell how deep a mold's roots go into a food. Do not try to cut off the visible mold and eat the rest! You will eat mold which is below the surface, which may make you sick. Don't do it...

Mycotoxins are poisonous substances produced by molds. They can cause nausea and vomiting, headaches, gastrointestinal discomfort, and other problems. As to the mold types which grow on margarine, they tend to not cause serious illness unless a person eats a lot of moldy margarine.

Margarine Storage Suggestions

Margarine's shelf life depends on whether it is the hard or soft type and the temperature. Hard margarine can be kept at room temperature for a day to a day and a half before it starts to break down. Soft margarine spreads are less robust at room temperature and should be refrigerated right after opening. At temperatures just above freezing - 33°F to 38°F (1°C to 4°C), margarine can last one to two months if opened and three to four months if unopened.

Margarine may be kept for an entire year if frozen.

Considering storage containers, airtight ones are best. Many people simply keep hard margarine wrapped in its original foil or waxed paper. It is better to move it to an airtight container. Soft, spreadable margarine should be kept in an airtight tub.

All in all, refrigerated margarine can last a long time - quite a bit longer than butter. It loses much of its robustness at room temperature, especially in hot climates. Keep it sealed it in an airtight container, and cold, for it to retain freshness for a long time. If it does become moldy, discard it. Frozen margarine can last for about a year, so you can stock up on it, and thaw enough for a few days at a time.

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