My plastic container bin used to be loaded with 1-quart yogurt containers, and I felt packaging guilt whenever buying a new tub, even when it was local and organic.
I knew that it wasn’t too hard to make yogurt at home — I had mental images of electric yogurt makers from the 1970s — but a “coincidence of information” (i.e., a series of web articles) showed me that I didn’t need an electric device or any fancy equipment.
Homemade yogurt is not as easy as grabbing a tub at the market, but there is something satisfying about doing it yourself, and it’s a chance to reduce your use of plastic.
Warm, Heat, Cool, Mix, Wait
Making yogurt at home is relatively easy but requires some organization and time. The process can be summarized as warm, heat, cool, mix and wait.
Warm: The first step is to wake-up the cultures. This will make them more active when it is fermentation time. A few hours before yogurt-making-time, I put 1-2 tablespoons (15-30 mL) of yogurt into a coffee cup and leave it out at room temperature. This yogurt is sometimes called the ‘seed’ yogurt.
The warm-up step is optional, but it reduces the chance of a fermentation failure. For the first few months of my yogurt making, I skipped this step and had pretty good results. These days I do the warming out of habit and as insurance.
Heat: Heating the milk modifies the whey proteins, which gives you a finer, more compact curd. A good target is 190 °F (88 °C), but if the milk gets a little hotter, it’s no big deal. You can heat the milk in a saucepan over gentle heat (ideally with a flame tamer underneath the saucepan to provide even heating), or you can use the microwave. I use my microwave, heating the milk in 5 minute bursts, checking the temperature after each cycle (you’d think I might know exactly how long to run the microwave, but you’d be wrong — I haven’t bothered to keep track). Or, if you want to be high tech about it, you could use an Arduino-based temperature monitor and alarm. (More on the science of yogurt from Harold McGee in the New York Times)
Cool: The bacteria that convert milk to yogurt have a preferred temperature range, so the next step is to cool the milk to that range, about 120 °F (49 °C). Set some timers so you don’t forget, and check periodically. For me, with the milk in a Pyrex measuring bowl on the counter, it takes more than 30 minutes (the exact time depends on the room temperature, air currents, etc.). If you are in a hurry, you could transfer the hot milk into a metal bowl and set that bowl on cold water (or, if you used a saucepan to heat the milk on the stove, put the saucepan in a bowl of water).
This is also the time to start prepping a warm spot for the fermentation. I use a flexible cooler, and add a jar of hot water to help keep the contents warm (it’s a cheap cooler, so not great at heat retention). If you have a piloted oven or have a heating device (like the hacked appliance described by Jennifer Jeffrey), skip this step.
Near the end of the cooling process, I also heat some water and pour it into the jars I’ll be using to make the yogurt to take their chill off.
Mix: Once the milk has cooled to the target temperature, pour a small amount of it into the container with the ‘seed’ yogurt, whisking as you pour to mix it thoroughly (“tempering”). Then pour the yogurt-milk mixture into the main milk container, and whisk to combine. Pour into clean containers.
I originally used 1-quart canning jars to hold the yogurt — they were OK, but a little bit too large (hard to get the last bits from the bottom of the jar) and the necks of the jars were hard to clean. In the last year or so, I have switched to the Working Glass from Crate and Barrel (my 10-year old glasses have a Luminarc mark on the bottom).
Put the lids on the containers and set them into warm place. I use a flexible portable cooler with good success.
Wait: Let the container sit in a warm place for a few hours until it sets. There are no fixed rules for this — I typically let the yogurt ferment for 4 hours or more.
For the first few years of yogurt making, I was careful about the 4 hour ferment — setting a timer each time I made a batch. This worked great, but made scheduling a bit challenging, especially on weeknights. So a few months ago I tried something new: let the yogurt ferment overnight. This means that I can easily make yogurt on a weeknight, or at the end of a weekend day. I take out the ‘seed yogurt’ at about 1 or 2 PM and let it warm up at room temperature. Then, around 7 or 8 or 9 PM, I start the heat and cool processes. I put the filled jars in the cooler, and when I wake up in the morning, the cultures have done their work and I have fresh yogurt to put in refrigerator.
Yogurt Making in Pictures
The drawings below outline the process.
Additional Thoughts On Yogurt Making
Many months after getting into a routine, I noticed that Paula Wolfert’s The Cooking of the Eastern Mediterranean has an appendix about yogurt and a recipe for making it at home. Wolfert writes that the most prized yogurt in the Eastern Mediterranean is made from buffalo’s or sheep’s milk because of the high butterfat content. She relates an old saying about the culturing process: “the quicker the sweeter.” In other words, the faster you can make the yogurt set, the sweeter it will taste, so some yogurt makers pour the warm milk-yogurt mixture into small jars for culturing. At 100 F, she writes, a batch of yogurt will jell in about 6 hours. At a lower temperature, it could take as long as 24 hours and give you a much tarter result. (Some day I should measure the temperature of my portable cooler during fermentation.)
Writer and editor Jennifer Jeffrey wrote about a clever way of managing yogurt culturing temperature with a hacked slow-cooker. By installing a dimmer switch in the power cord, she could control the amount of energy reaching the cooker’s heating elements, thus controlling the temperature of the water bath. (Important note: If you are going to hack commercial appliances, be sure you know what you are doing and follow good safety practices!)
After all of these words, remember that there are many ways to make yogurt at home — the yogurt cultures are somewhat forgiving about time and temperature — and what works for me might not work for you. Other authors might have methods that fit your schedule and taste preferences.
(Originally published on 1/9/11. Major update, 4/2/17: revised the instructions, added a diagram showing the basic steps. Minor update, 3/17/19: added instructions for overnight fermenting.)
I use the microwave to heat my milk. It takes about 14 minutes to get to 185 degrees. I stir at the 5 and 10 mimute marks and take it out just as it starts to boil. Don't stir right away though or it will boil over.
Marc, great job teasing the specifics out of this yogurt process. As you said, my technique is very similar. However, the milk I use is whole "creamtop" from the local dairy that delivers to our home, plus some of their excellent heavy cream. The milk and the cream are the kind that develop a clot at the top that you have to eat with a spoon. I mix 3 cups milk plus 3/4 cup cream, which seems to be the exact amount that will fit into the typical 1-quart mason jar. I know your readers probably despise Styrofoam, but since we happen to own a small Sytrofoam cooler, I place the yogurt mixture in there with a couple of jars of hot water. And because I want to reduce as much as possible the lactose in the yogurt, I let the bacteria continue their feeding for up to 48 hours before I remove the yogurt from the cooler. As Harold McGee has explained, however, its the length of time the milk remains at high heat–not the fermentation process–that determines the thickness of the yogurt. Except maybe in the case of Greek-style yogurt, which is drained.
Yes, a lot of people I know do use the microwave to heat milk – but remember what Euclidafarms says about heating and protein clumping/thicker yogurt. I think our Senor McGee says something similar.
To make the process even more low maintenance (and allow me to be even more distracted), I plonk a pot watcher into the milk boiling pan (set on medium heat). Then I don't need to pay attention to the pot till I hear some serious and steady clanking.
Also I don't really understand the devotion to jars at all – hard to get to the bottom of the jar etc. You can use just about any container to make yogurt. Those wide round storage containers, Anchor and Frigovere wide round storage containers. Spill proof lids are a plus but in South Asia, people make routinely make yogurt in regular handle-less wide mouth stainless steel pots and just plonk any old lid on top.
You don't discuss another problem which plagues some yogurt cultures and makes beginners thrown in the yogurt towel – "ropy" yogurt. For explanation of ropy polysaccharides see p. 165-167 of http://books.google.com/books?id=Sabnh9l76W0C&pg=PA165&dq=ropy+polysaccharide+yogurt#v=onepage&q=ropy%20polysaccharide%20yogurt&f=false.. [Google for more on S.thermophilus and ropy strains.]
One-quart Mason jars are not perfect, but they work for me. I like them because 1) they fit efficiently into my dishwasher (the tallness that makes emptying them difficult is an advantage in the dishwasher — their aspect ratio is efficient), 2) I have lots of them, so there is always a perfectly clean one in my cupboard, 3) I have plenty of lids for the glass jars, so one is always at hand, 4) they fit nicely into my crowded refrigerator. To get the yogurt from the bottom of the jar I acquired some long-handled teaspoons.
Do you use quart mason jars to store all your other prepared/cooked foods too? I wonder about cultural preferences** because I've often seen people use other (albeit glass) containers for soup or braised dishes say, but feel that yogurt must be made jars.
**: Though the mason jar has made a serious comeback in the Bay Area more recently. For example, several of my fellow hikers brought their non-liquid lunches in mason jars today.
Glass 1-quart Mason jars make up the backbone of my dry goods storage — I must have 30 in my pantry holding flours, grains, dried fruit, etc. I use them far less frequently for wet goods in the refrigerator, mostly because of their narrow necks (even wide mouth are too narrow). Off the top of my head, the current quart Mason jars in my refrigerator hold soup, sourdough starter, and yogurt (and two days ago I used two jars to infuse water with kombu and shiitake for the next day's Japanese stock).
If you're in a hurry, an ice bath will considerably reduce the cooling phase.
If you are interested in economy, powdered milk works for yoghurt just fine.
I like the idea of making my own yogurt in mason jars. I’ve made yoghurt a few times and always did it with a random assortment of bowls, (often without lids).
Have you ever considered straining to create a greek yogurt texture?
Thanks for the diagram. It helps.
I’m glad the diagram helps clarify the process.
I am not a fan of Greek yogurt (too pasty), so I haven’t thought much about straining. I might have done it for a specific recipe (probably one from Ottolenghi’s Plenty, which seems to have Greek yogurt in nearly every recipe), but am not sure if you could strain and then store it. It might work, if you were careful to have very clean implements and containers. Of course, when the yogurt is exposed to air and surfaces there is a chance of contamination.