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There is nothing worse than opening a container of yogurt only to find it has little green fluffy growths dispersed all over the surface. Actually there is, not noticing the green fluffy growths until the first spoonful. To prevent such an experience it is important to know how to store homemade yogurt and how long it will last during storage.
Store homemade yogurt in the fridge at a temperature between 40-35℉ (4.5-2℃) with a sealed lid, use clean utensils when dishing out yogurt and do not replace leftover yogurt back into the container. Molds are aerobic, resistant to low pH environments and consume complex carbohydrates.
The main spoilage organisms of yogurt are molds. Molds produce mycotoxins which are compounds which protect its environment from invasion from other competing microorganisms. Mycotoxins produce the off smells and flavors which indicate your yogurt has gone off. Not only do they taste bad but they can be toxic.
Molds grow well in warm conditions with easy access to oxygen, they can use any type of carbohydrates as an energy source and can grow rapidly in warm environments. It is for these reasons why it is important to keep your homemade yogurt in the refrigerator in a sealed container.
Homemade yogurt has fewer complex carbohydrates than store bought because most store bought yogurt contains thickeners which help to maintain its texture during transportation. Unless you are after extra thick yogurt it is rare that a yogurt recipe contains any added thickeners like cornstarch, guar gum or agar agar. If you are interested in ways to thicken your yogurt checkout this article about various ways to thicken homemade yogurt.
How to store homemade yogurt after opening
After you have opened your homemade yogurt it gets exposed to oxygen and heat which give spoilage bacteria access to the yogurt. Yogurt when properly incubated will have a pH below 4.0 which is below the recommended pH by the WHO to be food safe. A pH below 4.0 inhibits the growth of many spoilage microorganisms including bacteria like Clostridium botulinum but a low pH does not prevent the growth of molds.
To prevent the growth of mold, keep your yogurt in a sealed container. Mold is an anaerobic organism (it needs oxygen to grow) by keeping yogurt sealed while in the fridge the growth of mold will be slowed, extending its shelf life.
Once your yogurt container is less than half full either transfer it to a smaller container or use the remaining yogurt quickly. This is because the extra space in the jar will allow more oxygen into the container each time you open it, providing the ever present mold a chance to grow.
How to store yogurt to extend its best before date
There are ways to extend the life of your homemade yogurt, all of which rely on the prevention of the growth of mold on the surface of the yogurt. Mold is pervasive in the environment and cannot be eliminated from the kitchen. It grows on any surface where there is any water and availability of oxygen.
The key to preventing mold from growing on your yogurt is taking advantage of mold’s two main weaknesses which can easily be used to slow its growth.
- Mold needs oxygen to grow
Mold in an aerobic organism, just like mammals it cannot survive without free oxygen in the air. Therefore to prevent the growth of mold keep your homemade yogurt in an airtight container and only open it when you need to use it. Replace the lid as soon as you are finished dishing it out.
- Mold likes warm environments
Mold grows quickly in warm damp locations with lots of carbs available. Since yogurt has many indigestible complex carbohydrates in it and it is a semi-liquid gel, two of these conditions are fulfilled just by the nature of your yogurt. The only remaining condition which you can control is the temperature. Therefore keep your homemade yogurt in the fridge except when dishing it out into serving dishes or directly onto your food.
Other ways to extend the life of homemade yogurt
Yogurt has been cultured way before the prevalence of refrigeration so there must be ways in which yogurt was preserved without temperature control. It is true that store bought yogurt needs to remain in the fridge simply because it is full of additives, has few bacterial strains and is made as cheaply as possible.
One of the benefits of making your own yogurt is you can control the ingredients you put into it. Basically you will need two ingredients: some type of milk and a starter. Both of these ingredients can affect the shelf life of homemade yogurt
How the type of milk affects the shelf life of homemade yogurt
Yogurt can be made from any type of milk. The usual choices are cow, goat and sheep but any type will gel into a yogurt product. Some milk types will make yogurt which will naturally last longer due to the various components of the milk.
Milk with a high lactose content will produce yogurt which will last longer. This is because the lactic acid bacteria in the milk use the available lactose as an energy source, producing lactic acid and other protective compounds. With a higher amount of lactose the lactic acid bacteria can produce more lactic acid then low sugar milks.
Low fat milk is higher in sugar than high fat milk and goat and sheep milk have more lactose and less fat than cow milk. Therefore yogurt made with these milk types can last longer than higher fat and protein milk types. For a very tangy and long lasting yogurt make yogurt with skim or 0% milk. The texture is less creamy and the flavor will be tangier than the high fat yogurt made with 10-14% milk.
How the type of starter affects the shelf life of homemade yogurt
There are many types of starters which can be used to make yogurt. There are types which need warm conditions (thermophilic) and some which can incubate in ambient temperatures (mesophilic), some have few bacterial cultures (one time use) and others have many (heirloom).
Heirloom yogurt starters are starters which can be used continually over and over without concern of weakening or contamination of the culture. This is because the culture is made up of many different types of bacteria and some yeasts which resist invasion from spoilage bacteria and mold. If you are interested in trying a heirloom yogurt culture here is an Amazon affilite link of collection of them. I have tried the Bulgarian cultrue which I have been using for at least a year continuously.
Just like mold, lactic and acetic acid bacteria produce compounds which protect their environment from invasion from unwanted microorganisms such as mold and other spoilage bacteria. These compounds are not toxic to mammals so they make great additions to yogurt as they improve the health effects of yogurt and extend its shelf life.
Incubate the yogurt for a longer period of time
As the incubation time increases the pH of the milk decreases. As the pH decreases the environment inhibits the growth of spoilage bacteria and increases the number of lactic acid bacteria, making it even more difficult for unwanted microorganisms from getting a foothold in the yogurt.
The incubation time used to make store bought yogurt is kept to a minimum as the longer it is incubated the more expensive it is to make. When making homemade yogurt you can incubate it for extended periods of time which increases its shelf life. For more information on the effects of extended yogurt incubation check out this article.
How long does homemade yogurt last?
The length of time homemade yogurt will last varies depending on the type of starter and the type of milk used to make the yogurt, how long it was incubated for and the temperature it is stored in.
Typical homemade yogurt will last two weeks depending on how it was made and stored. As it ages it becomes increasingly tangy so for sweet yogurt, consume it within a week. For sour yogurt use older yogurt which has had a longer time to acidify.
If you used store bought yogurt or one time direct set yogurt starter then after two weeks begin to watch for mold growth on the surface of the yogurt or around the lid of the container. These types of starters only have two to four lactic acid bacteria strains in them making them susceptible to spoilage.
If you make your yogurt using a heirloom type of yogurt starter your yogurt should last much longer. Some heirloom yogurt cultures are hundreds of years old and have been handed down from parents to children for generations. These cultures are very robust and contain many types of bacteria which work together to protect itself from infection from spoilage bacteria.
Yogurt made with these types of cultures will last longer but as they age the yogurt continues to sour and the population of the culture shifts to favor those bacteria which prefer acidic conditions. For a healthy heirloom culture make smaller batches of yogurt more often rather than larger batches less frequently. This will keep your yogurt fresh and sweet as the remaining lactose in the milk sweetens its flavor.
How do I know if my homemade yogurt is bad?
Once you have been making yogurt for a while you may end up with a jar of it being pushed to the back of the fridge and ignored for a period of time. When the time comes to clean out the fridge do you just pitch it all or do you check to see if it is still usable? If you are like most people you will have to open it and give it a smell and inspect it, even just because you are curious.
Homemade yogurt which has gone bad could smell rancid, have mold growth on its surface or around the top of the lid or it could have yeast growth giving it an off smell and a fizzy texture. Each of these are good indications that your homemade yogurt is past its prime. Pitch it and start again.
When it comes to knowing when something has gone off or not just trust your instincts. If your yogurt smells bad, has a strange texture or color and seems to be pressurized in any way then it is safe to say that something has gone amiss. If you have incubated your yogurt properly you will not have to worry about the more dangerous bacteria and mold species which can infect milk products but yogurt which is past its prime doesn’t taste very good. To be safe just pitch it.
For a complete explanation of how to make yogurt at home check out this recipe but as a reminder here are the three most important things to remember while making yogurt:
- Use only fresh milk which is well before its best before date
- Use clean utensils and containers
- Pasteurize the milk before incubation