Mark Frauenfelder describes how he makes yogurt with a yogurt machine. Made by Hand, his new book, has a chapter about fermented foods.
Let me add my two cents. After several years of making yogurt, I finally figured out there are two crucial steps: 1. Denaturing (expanding) the milk proteins. 2. Growing the bacteria. They require different temperatures. The milk proteins, as far as I can tell, denature at temperatures starting around 130 degrees F. You want the milk to be in that range for an hour or so. Below that temperature, the milk proteins curl up again unless bacteria get in the way. The best temperature for growing the bacteria is said to be around 110 degrees F., although I’ve found that incubation at 92 degrees F. also works.
So the ideal process for making yogurt is something like this: 1. Keep the milk at 140 degrees for a few hours. 2. Add the starter bacteria. 3. Keep the milk at 110 degrees for a long time, say 12 hours. I have a yogurt maker that approximates the initial higher-temperature phase by having you add boiling water around the container. The first time I tried it I was surprised how well it worked (how creamy the yogurt was) because it was much simpler than the usual recipes where you boil the milk, let it cool, and so on — and which after all that produced mediocre results. It took me a long time to realize I’d get even better results with my yogurt maker if the milk was warmer when I started.
Even on a stovetop, I think it would be easier to raise the temp to 130 F and keep it there for an hour, then let it cool back to 110 F than it is to bring it up to 180 F and then let it cool back to 110. The problem with boiling is if you get distracted (say by attending to a child) the temp goes too high. Using low heat and a timer would be much easier and less risky IMO. Anyway, I’ll give this a try for my next batch.
Just to clarify, you are saying that your yogurt maker heats the milk to 110, but you add boiling water to get it up around 140 for a few hours?
I’ve never heard of keeping the milk at the higher temperature for a few hours to denature the proteins. I thought the initial heat was just to kill off competing bacteria. However, that explains why I get much creamier yogurt when making it in my crock-pot than on the stove. It takes much longer to heat and cool the milk when using the crock.
It would be nice if slow cookers had more temperature settings. If I could get my crock to stay as low as 110, it would further simplify the process. As it is, I pour the milk into a jar and stick it in a cooler, wrapped in a blanket with a hot water bottle.
Just to clarify, you put the starter in while the milk is at 140F, cool to 110F and incubate for 12 hours or so? And adding the bacteria while the milk is above 130F results in a creamier texture to the final yogurt? Is 140F anywhere near the temperature that will kill the starter?
Sadie, yes, your impression is correct, except that it reaches the higher temperature (around 130) for less than two hours.
David, I put the starter in when the milk is about 130 F.
What produces the creamier texture is more denaturing of the proteins simultaneous with bacteria growth. It’s not the temperature at which I add the starter that causes the improvement, it’s that there is a substantial length of time at the temperature that denatures the proteins. So the proteins become more denatured than if I heated the milk to boiling and let it quickly cool. This is what conventional yogurt recipes miss — the value of long denaturing.
I don’t know what temperature will kill the starter. Apparently 130 F. is safe.
I thought yogurt makers were too expensive and too low capacity. I use a cooler ($25) and an aquarium heater ($30).
First, I denature by bringing the milk to 180 on the stove at low heat (I set the stove’s dial to 2). I cool it to 115 or 120 before adding starter. All this is easy with a digital kitchen thermometer ($15). The milk is above 130 for about two hours, and far above 130 for much of that time. If you try this and the milk burns just heat it more slowly.
Put some warm water in the cooler. Use the heater and thermometer to maintain the water temperature at 110. The first time, it takes some a few tries to set the heater’s power output knob correctly. After that it rarely needs adjusting or monitoring.
Put the container(s) of the yogurt and starter mixture into the cooler. I use the handy half gallon glass jars that my kimchee comes in. I ferment it for 36 hours or so. Usually I make one gallon but the cooler has a 2.5 gallon capacity.
This makes thick and tangy yogurt. I’ll try adding the starter at a higher temperature to see if it’s thicker, but really it’s think enough as is. The elapsed prep time is two or three hours but the total work time is certainly under 5 minutes.
This was a great tip, I’d never seen anything about ‘heat and hold’ before. But when I googled, and ran into excerpts from a reference book, Development & Manufacture of Yogurt. The link is an authorized sample, and gives quite a bit of information about yogurt culture. The heat treatment section starts on page 73.
https://books.google.com/books?id=zMCDLlcRaQkC&pg=PA92&dq=development+manufacture+yogurt&hl=en&ei=oXM7TIeFNYfWtQOLqanaCg&sa=X&oi=book_result&ct=result&resnum=2&ved=0CDYQ6AEwAQ#v=onepage&q&f=false
I found one other link that mentioned heat and hold. It suggests heating to 185F and holding for 10 minutes, or 20 minutes for thick yogurt. The commercial guideline (first link) was 30 minutes at that temperature. I tried 15 mins. and 30 mins., and both were thick.
https://www.uga.edu/nchfp/publications/nchfp/factsheets/yogurt.html
The recommended amount of culture has increased over the years, not necessarily a good thing. Sandor Katz (Wild Fermentation) uses 1T. fresh live culture per quart of milk, quoting Joy of Cooking (1964 edition) explanation why more culture is not better — Lebensraum. That 1T per quart was how I made yogurt for years. My 1976 Joy edition still has the Lebensraum explanation, but they quadrupled (!) the culture quantity.
My hesitation about 130F inoculation is that I have 6 different cultures in my yogurt, and not all may be hardy at 130F. Nice to know, though, that culture can survive at higher temperatures than commonly thought. And it was especially nice to learn about denaturation.
This is the best I’ve tried.
Bring your milk to 180.
Let set till the temp goes down to 110, about an hour or so.
Add your starter. (I use l cup of my latest batch of yogurt for 2 quarts of milk).
Let set in machine till thick, about 3-4 hours.
I make fresh yogurt every 3-4 days to keep the good bacteria live and fresh.
I bought yogurt machines made in the ’70′s, they sell them at thrift stores and flea mrkts. very cheap.
For thicker, creamier yogurt add l cup of powdered milk before heating.
I think maintaining a fairly warm temperature during culturation also helps make better yogurt. After reading this post I made a batch with a 3.5-hour preheat up to 180 degrees, a short cool-down to 110, and then I put three quart jars of yogurt into a cooler lined with a wool blanket. I also added two quart jars of boiling water to the cooler. I used whole milk and no powdered milk, which is my normal procedure. The culturation time was 8 hours, and it was still almost hot in the morning when I took it out.
This produced the thickest, creamiest yogurt I’ve ever made, tangier than store-bought, but (to me) perfect. There was no visible whey separation at first, but after I took some out of the jar, whey appeared on top. I think this means the proteins were unwound enough to bind up most of the whey.
Hey, Thanks for all the tips. Can someone say how much time it takes to bring the milk from boiling to 110F for say 2 Quarts. Is 45 mts the time (I dont have a thermometer).
Nice little discussion, especially the book link, thanks.
My notes, going entirely for taste (health, schmealth:
– yogurt makers are cheap. The Yogourmet is under $50, includes a decent thermometer and makes half a gallon. It’s less-than-no-frills, so test and fiddle (e.g., in a warmer kitchen I’d probably put it on a dimmer for bath temp).
– starter matters. I use my favorite brand (Brown Cow), which is a pretty standard yogurt (Bulgaricus/Thermophilus)-and-probiotic (acidophilus/bifidus) mix. Experiment.
– milk matters. Again, my favorite milk (whole from Clover) is also my favorite for yogurt. Use what you like best, not any stale old half gallon.
– cleanliness matters. I killed one batch, maybe with phages (it didn’t smell ‘bad’, but was watery and not right). Wash your hands. Transfer a starter-size amount to a clean, tightly capped container in the fridge.
– culturing time affects live mix a lot. Too short or too long gives a one-note symphony where just one or two strains dominate. This naturally gets propagated into any subsequent run. In my case, ~10 hours seems ideal. This probably varies a lot by temperature, strain mix and taste.
Now if only I knew where my cheesecloth bag had gone..
I’m so glad I found this blog. I think I made yogurt this way by accident yesterday and have been trying to figure out why it was so good. I brought the milk to 180+ and held it there for about 10 minutes. But, then I let it cool naturally in a small microwave that holds in heat for almost 2 hours. Had to heat it up a little before adding the starter. Then I let it sit in the microwave overnight, having zapped it a few times before I went to sleep. It was the best I’ve made. I used whole organic milk with 2 tblsp. of yogurt made from a bulgarian starter I ordered off the internet.
When I took it out the next morning it had a custard texture which I love. I strained the whey for about an hour or so.
I did not use my donvian yogurt maker because I didn’t want to bother with the small containers. I made it this way because it was almost no work and I wasn’t being that precise about anything. In fact, I was being lazy and took a chance that I didn’t ruin anythng.
I believe that using at least two quarts of milk was important because it took the milk longer to cool down before I added the starter thus creating the “time at a high heat” which apparently made it thicker.
Here’s my only problem. I ate almost the whole thing myself. (with blueberry, all fruit, no sugar added preserves) Hopefully, when the newness wears off, I’ll be more normal in how much I eat! LOL
Thanks for this advice, I find it’s true that holding at the higher initial temp produces thicker yoghurt (I do it for an hour, after experimenting with both shorter and longer times and finding that 1 hour is the sweet spot. 2-3 hours also works, but it doesn’t make the yoghurt noticeably thicker). My question is this: does the effect of the denaturing get ‘undone’ if you add the bacteria in at 110 degrees or 120 degrees? That is, do the milk proteins curl back up if you let the milk cool? Also: is heating to 140 and holding there any different/better/worse than heating to 180 and holding there? Finally: I usually incubate the yoghurt at 120 degrees, but I see a lot of people use lower temperatures (even as low as 92, you mention)–what are the advantages and disadvantages here? I am lucky enough to have an oven that can produce consistent low heat, so I am free to set my oven to whichever of these temps is best, for either the denaturing or the incubating–I’m just wondering about pros and cons.
I use a crock pot modified into a sous vide machine. It allows controlling the crock pot at exact and constant temperatures.
My next MOD is to use an air lock type contraption on the lip similar to a picklemeister.