My post on How to Make Yogurt is so popular (about 1/4 of all visitors to Sustainable Suburbia visit that page), and has generated so many comments and questions, that I figured it was time to formalise some of the answers into a kind of FAQ of yogurt making. So I’ve spent the last few days reading books and websites, trying to come up with some definitive answers to both my own questions, and the most common ones I am asked.
I have some more questions & answers in the pipeline, and feel free to add more questions or comments in the comment section at the bottom of this post.
There are a number of possible reasons for this, the biggest problem people have with making yogurt at home. Firstly, most homemade yogurt is not going to be as thick and creamy as store bought yogurt, simple because it doesn’t have the additives. There are things you can do to make your yogurt thicker (see How do I make thicker yogurt?), but this topic is really about yogurt that hasn’t set, or hasn’t set properly. Or hasn’t become yogurt at all!
The most common reasons for this are:
- Your starter culture was too old. This may not be at all obvious until you have your yogurt fail like this. You need to understand that a) your next batch of yogurt should ideally be made before the last batch is a week old. So if you are using yogurt from the store, consider that it could be too old before you even pick it up – make sure you buy the freshest yogurt you can. And b) most store bought yogurt (including Easiyo sachets and the like), are made with a ‘direct set’ culture, which can not be reused (or regrown) more than about three or four times. So unless you are buying an explicitly ‘reusuable’ culture, you should refresh your yogurt starter every few batches.
- Your starter culture can also die if it is exposed to a high heat, so make sure your milk has cooled down to 43C (110F) before mixing in the culture.
- The temperature was not kept high enough. If the milk cools down too much before the yogurt has formed, then the yogurt bacteria will struggle to grow, and meanwhile the milk bacteria can multiply more quickly than your starter culture, killing it. Minimising the milk bacteria is one reason for heating the milk to near boiling before beginning. But even boiled milk will go off if you leave it sitting at room temperature. If you are using an Easiyo, try checking the water temperature after a few hours. If it has cooled, carefully remove your yogurt container after a few hours and replace some of the water with freshly boiled water. You can also wrap it in a blanket to help keep it warmer for longer. See Why does my Easiyo not keep the yogurt warm enough?
- You may have used too much culture. I know this seems counter intuitive but if there is too much culture, the bacteria will be fighting over the food (milk sugars) which then runs out before the yogurt sets. About 2 tablespoons of an Easiyo yogurt powder or a fresh yogurt is generally enough for a litre of yogurt. If you buy the culture itself, you should follow directions supplied with it (it will be much less than 2 tablespoons).
- Your yogurt container was not clean, and the contamination (which could be as simple as left over dish soap) has harmed the starter culture.
Okay, so you don’t have any of the problems listed above, but you would like your yogurt to be thicker. There are a number of things you can do.
- Use higher fat milk. The higher the fat content, the thicker the yogurt. If you are not particularly worried about fat content, try adding 1/4 cup of pure pouring cream. It makes a big difference. A creamier yoghurt is usually sweeter too, so you may find the higher fat content allows you to reduce the sugar you need to add.
- Add some powdered milk. If you are just using fresh milk to make your yogurt, adding about 1/4-1/2 cup of powdered milk can help thicken it up a little.
- Heat the milk to 85 (185F) degrees Celcius and keep it there for 30 minutes (remember to let it cool before adding your starter culture). One of the reasons for heating your milk before making yogurt is to ‘denature’ the protein, casein, which allows the yogurt to coagulate more effectively. Heating for a longer period denatures more of the protein.
- You can also use non-milk additives like agar agar, tapioca or gelatin. These can be added just before adding the culture, or, if you are going to reuse your culture (ie keep a bit of your yogurt for making the next batch), wait until the yogurt is just finished, but not yet refrigerated, take a little out for your next batch, mix through your thickener and refrigerate.
- How thick your yogurt is can also be a function of the type of culture you use, so if you want to explore this further you could look at buying particular cultures, for instance you could try Type C aBY if you are in Australia or take a look at Cultures for Health for comparisons between their cultures, but they only ship within the United States and Canada.
Short answer: Probably not.
Longer answer: Only if you weren’t using enough in the first place. If you were using enough, you may end up with thinner, or completely runny yogurt. As explained above, this is because if there is too much culture, the bacteria will be fighting over the food (milk sugars) which then runs out before the yogurt sets.
Why do you have to get new yogurt starter every three to four batches? I’ve heard about people in traditional cultures using the same starter for generations!
This is an issue of ‘direct-set’ vs ‘reusable’ cultures. Most commercial yogurt and yogurt sachets use a direct set culture, which can only be reused a very limited number of times.
Additionally, different cultures will die off at different rates, so if you are using a starter yogurt with more than one bacteria in it (which is common), after a couple of batches the balance will be off, which can affect yogurt consistency and flavour.
Reusable cultures do exist, and are available from places like Cultures for Health in America and Canada. I haven’t found anywhere online in Australia that sells it yet (I mostly just use a couple of Tbsp from an Easiyo sachet for every few batches, or buy some fresh yogurt to use).
Because the original pasteurisation killed the natural milk bacteria, leaving the way open for other ‘bad’ bacteria to grow. This is why pasteurized milk still has a limited shelf life, even when refrigerated. Also, heating for a longer period of time will ‘denature’ more of the protein and produce a thicker yogurt. See How do I make thicker yogurt? above.
Note that you can make yogurt with raw milk, with the natural milk bacterias intact (although raw milk cannot be sold for human consumption in Australia), without this step, but it will not be as thick. This is because heating the milk also ‘denatures’ the milk protein, allowing it to coagulate more easily.
No! This is the subject of my first yogurt post: How to Make Yoghurt From Scratch in an Easiyo Yogurt Maker. It is very easy to make yogurt from yogurt (and milk) in the Easiyo without buying yogurt sachets.
There are a few possibilities. Is it cracked? Is the lid not sealing properly (has the plastic warped)? Have you immersed the thermos in water? The manufacturer says not to do this, I’m presuming because if water were to get into the space inside the walls of the Easiyo it would no longer hold the heat.
I have found that sometimes the water cools early. I don’t know why – maybe I didn’t use it in quickly enough after it boiled, or maybe it was just a very cold day. Mostly it’s not an issue, but I have been successful in taking the yogurt canister out of the Easiyo, replacing some of the water with some freshly boiled, and replace the canister. This seems to work, though I don’t usually bother.
Image credit: Mary Thompson