Storing EM and diagnosing a failed EM-A: shelf life, storage, smell, color, and pH

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EM are living products. Like a sourdough starter or yogurt, they keep well if you follow a few rules, and they eventually run out of steam if neglected. They also have a few quirks that turn out to be harmless, such as a swollen container or a white film on the surface… which often cause needless worry.

This guide covers the shelf life of each product, the right way to store them, and how to tell a successful EM-A from a failed one, with what to do in each case.

How long do EM keep?

Shelf life varies from product to product, and sometimes from one set of instructions to another. Here are the guidelines we go by:

• EM-1 (concentrate): its microorganisms stay dormant until it is activated. The date printed on our bottles is the expiration date, about 2 years after production, as long as the cap stays tightly closed; other licensed producers state about 6 months. In every case, the date printed on the label is the one that counts. Once a bottle has been started, it takes in a little air every time you open it: close it tightly and don't leave it sitting around.
• Microferm EM-A in Bag-in-Box: until the expiration date printed on the packaging, about 1 year after production. The pouch shrinks as it empties, which limits contact with air down to the last drop. Bottles, on the other hand, take in air every time they are opened.
• Homemade EM-A: this is the most fragile. The manufacturer of our EM-1 recommends using it within a month. Other technical data sheets give 35 days ideally and 65 days at the very most, and some producers, who activate at higher temperatures, don't go beyond two weeks. Lab counts on an activated solution showed a significant drop in lactic acid bacteria within a few weeks.

Our advice: use your homemade EM-A within 1 to 2 months, and the sooner the better. After that, it isn't dangerous, but it contains fewer and fewer active microorganisms.

Key takeaways

Concentrate: according to the date on the label (up to 2 years for ours). Microferm in Bag-in-Box: according to the expiration date on the packaging (about 1 year). Homemade EM-A: 1 to 2 months. The more “awake” a product is and the more it is exposed to air, the sooner it needs to be used.

Storing your EM properly

• Somewhere cool, but never freezing: a room at moderate temperature, a basement, a pantry. Technical data sheets put the storage range for EM-1 at roughly 37–100 °F (3–38 °C); the ideal is still a stable room temperature, around 59–77 °F (15–25 °C). Freezing kills the microorganisms. A refrigerator isn't necessary.
• Away from light and direct sunlight: a garage in midsummer or a windowsill won't do.
• Tightly closed: air lets in unwanted microorganisms. Always screw the cap back on right after use.
• In a full container: when the level of your homemade EM-A drops in a large container, transfer it to smaller bottles filled to the brim.
• In plastic rather than glass: EM keep producing a little gas, and glass doesn't handle pressure well.
• Away from household cleaners: bleach, disinfectants, and chlorinated products destroy the microorganisms. Never reuse a container that has held them.

Emy's tip

Keep your EM in a closed cardboard box at the back of a cabinet in a room at moderate temperature. The box protects them from both light and temperature swings.

Good or failed: recognizing an EM-A by its smell, color, and pH

Three criteria are all you need. Check them as soon as activation is complete, then from time to time during storage.

A successful EM-A

• Smell: sweet and sour, pleasant, fruity, slightly vinegary.
• Color: orange-brown, lighter than the original molasses.
• pH: 3.8 or below, ideally between 3.2 and 3.6.

A failed EM-A

• Smell: rotten, like sewage, rotten eggs, rancid butter, or ammonia.
• Color: still very dark, or cloudy with colored patches.
• pH: above 4, and not dropping even after a few more days somewhere warm.

pH has the final say. pH paper, such as our pH test strips, is inexpensive and takes the guesswork out. If the smell is good but the pH is still slightly high after 7 days, it's often just a matter of warmth: leave it somewhere warm a little longer and test again. But if the pH stays above 4 and the smell is bad, the balance of microorganisms isn't right.

White film, putrid smell, swollen container: what should you do?

A white film or flakes on the surface

This is normal. It's yeast, which is part of the culture. A little sediment at the bottom of the container is normal too. If the smell and pH are good, you can use your EM-A without worry.

Fuzzy green, blue, or black mold

This means air has gotten in or the container wasn't cleaned properly. In a liquid, don't try to remove it: if it comes with a bad smell, the EM-A needs to be replaced.

A putrid smell

This is the clearest sign of failure. There's no point waiting it out or adding more EM-1: start over with a clean container.

A swollen container or pouch

This isn't a problem in itself: EM produce gas. For a container, gently loosen the cap a quarter turn to release the pressure, then close it again. A slightly bulging Bag-in-Box pouch is normal. What matters is the smell.

Did you know?

According to the manufacturer, almost every failed EM-A comes down to one of two causes: a poorly cleaned container or a temperature that fluctuates too much during activation. Cold and chlorinated water round out the list of usual suspects.

Why an activation fails

To get it right next time, go through this checklist:

• The container: poorly rinsed, or with traces of household cleaner.
• The water: chlorinated, because it wasn't left to stand for 24 hours.
• The temperature: too low, or rising and falling between day and night.
• Air: a half-empty container, or one opened too often.
• The concentrate: too old, poorly stored, or frozen.
• Re-culturing: an EM-A made from another EM-A, which manufacturers advise against.

You'll find the full method, with proportions and temperatures, in our guide Activating EM-1: making your own EM-A step by step.

What to do with a failed or old EM-A?

A failed EM-A should never go on plants, whether watered in or sprayed: you would be introducing microorganisms you know nothing about. The simplest option is to pour it onto the compost pile, away from plants, where it will be diluted and broken down along with everything else. We explain how to use EM in compost in the guide Speeding up your compost with EM.

An EM-A that is simply old, still smells good, and keeps a low pH isn't “failed”: it's just less potent. Use it first for compost, and save fresh EM-A for seedlings and the vegetable garden.

To avoid waste, make small batches sized for one or two months of use. And if you only use EM now and then, Microferm EM-A Active Solution, ready to dilute, keeps much longer than homemade EM-A. For regular use and large volumes, EM-1 Concentrate remains more economical. The same storage principles apply to fermented bran for bokashi: see our guide on bokashi bran.

In summary

EM should be kept cool, away from light and freezing temperatures, tightly closed, and in a container that is as full as possible. The concentrate keeps until the date on its label (up to 2 years for ours), Microferm in Bag-in-Box until the expiration date on its packaging (about 1 year), and homemade EM-A should be used within 1 to 2 months. A good EM-A smells sweet and sour, has an orange-brown color, and has a pH of 3.8 or below; a white film or a swollen container is normal. A putrid smell and a pH that stays above 4 mean the batch has failed: pour it onto the compost, never on plants, and start over with a clean container and a stable temperature.

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