Friday, September 2, 2011

How Many Times Can You Make Yogurt from the Same Starter Culture?

One of the most common questions I get from users of my website has to do with reusing their current batch of yogurt to make their next batch. Being able to "reuse" or perpetuate the starter from one batch to the next can be a huge cost savings in making yogurt, completely eliminate packaging waste, and to gain even more control over the finished product as compared with starting from a new starter culture each time. But like a lot of my users, I have not had great success with keeping a starter going beyond four or five batches, before noticing a dropoff in quality of the finished yogurt. Until now that is.

As a quick review, the first time you make yogurt at home you need a starter and some milk. I recommend using 2-3 Tbs. of a high quality, store-bought, plain yogurt, such as Dannon or Stoneyfield. Alternatively, you can purchase freeze-dried cultures from health-food stores or online. Once you have made your first batch of yogurt, you can reserve 2-3 Tbs. of it to start your next batch, eliminating the need to buy more store-bought yogurt or cultures. Theoretically, this should work indefinitely, and in homes where yogurt making is a multi-generational tradition, it does. Yet, I have observed my yogurt starting to get less thick and less tangy by batch five, and have shied away from going beyond four batches for several years.

Back in June of this year, however, I decided to give perpetuating a culture another go. So I read up on yogurt cultures, and re-examined my process for defects. What I learned is that not all yogurt cultures are capable of continual perpetuation. Some cultures are "direct set", meaning that you use them once, and that is it. You need to buy new starter for each and every batch. Many freeze-dried cultures that accompany home yogurt makers are of this variety. Other cultures, however, are capable of being perpetuated indefinitely - under the right conditions. Two of the most common are almost always found together in good quality yogurt. They are Lactobacillus bulgaricus and Streptococcus thermophilus. They also happen to be the two strains found in Dannon plain yogurt, from which I started this latest experiment.

The other thing that I learned is that the longer your current batch of yogurt sticks around in the fridge, the less likely it is to be a good starter for the next batch. I sort of knew this intuitively, since we've all had yogurt go bad on us before we could finish it. But as long as the yogurt hadn't "turned", I figured it was okay. But if you think about the yogurt making process, the clock is ticking on those cultures for lack of anything to eat. Remember, the bacterial cultures in yogurt consume the lactose in the milk, converting it to lactic acid. This not only gives yogurt its distinctive tanginess, it also preserves the milk by creating an acid condition in which pathogenic bacteria will not grow. So your finished yogurt has much less lactose in it upon which the cultures can feed. Eventually, they run out of fuel entirely and die, and the bad bacteria moves in.

So how long is too long? I don't really know, and am open to comments from any biologists in the audience. But since June, we have been awash at our house in various forms of fresh berries followed by jams made from said berries. As a result, our yogurt consumption is way up. Our family of three has been ripping through a half gallon of yogurt in about seven to eight days. So the batch that will become the next starter is never more than 8 days old. However, we went out of town twice during this experiment, and I froze 2-3 Tbs. of the current batch, and picked it up anew upon our return. We will finish batch number seven this week (I know that's a whole lot of yogurt) and I will be making batch number eight this weekend. So far each batch has turned out just like the batch before it. Now I don't have commercial heating and freezing equipment in my home (I am sure you don't either) and there is certainly going to be variability in how cold it is in your fridge vs. mine. With that said, if you make a new batch - or freeze some starter from the current batch - within a seven or eight days, my results seem to indicate that you can keep these two strains going indefinitely. Time will tell of course, and I would not plan on freezing your cultures for more than a few weeks.

I will continue with this experiment for as long as I can, and provide updates in the form of comments to this thread. Please track my results and chime in with your own findings.

92 comments:

  1. I found your website online, and have used your methods, religiously, and have excellent yogurt, every time. I love the whisking advice, it really makes a difference.THANKS!!!

    Am I understanding your new experiment correctly - you make yogurt, immediately take out the 2 tablespoons, freeze it, and then use it for the next batch? Makes good sense, I'll try it.

    Please, allow me to share my twist on your method. I recently insulated the garage with styrofoam boards, and I had a bit left over. I also had an empty cardboard box - it held a paper shredder - the top is one of those which has two side flaps and one large flap, similar to this style,

    http://www.alibaba.com/product-gs/337602979/For_storage_box_tongue_type_single.html

    I cut the styrofoam to fit one piece in the bottom, and each of the four sides, but two pieces on the top. I put my yogurt into two quart jars and put them in the box, along with another jar of hot water (from the hot water bath pot) and then I put on the styrofoam lids, and close the top of the box.

    At the first, I poked a hole in a jar lid, and suspended a thermometer in the yogurt, and this arrangement kept the yogurt at 110 for the entire 9 hours of culture-time. Then the jars go straight into the 'fridge.

    I use mason jars with the two piece tops - the metal ring and metal cap, only I replace the metal cap with a circle cut out of an old yogurt-container-lid.

    Anyway, thanks so much, you've revived my love of making my own yogurt. I love your system, and I think it makes the whole thing pretty foolproof. Thanks so much.

    Cheers!
    Rosemary

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  2. Rosemary,

    Thanks for sharing your tip. I have toyed with the idea of a thermal approach, and reusing your hot water bath is basically making this almost a zero-energy affair. But I have always felt that the temperature must be slowly dropping the whole time. We've all had hot soup in a thermos be "pretty warm" soup by lunch time. Even with the addition of the hot water (which is also cooling) I don't see how the temperature could be steady for 7-8 hours. Perhaps I'll give it a whirl.

    By the way, I don't use a whisk when making yogurt. I think you have my site confused with some other.

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  3. Rosemary,

    To your other question, I only freeze it if it looks as though I will not make a new batch within the 7-8 day range.

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  4. Batch eight in the books and perfect!

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  5. Last time I bought a starter I had the Dannon in my hand and then I switched and bought Stonyfield! Damn! Oh Well, next time. I would like to say Thank you SOOO much for your site. I have been making yogurt after reading your instructions for about 4 months now and I could not be happier!! I love it. I like to sweeten mine with real maple syrup. It works great! M.K.

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  6. I prefer FAGE over Stonyfield and Dannon. I just checked and it does have the necessary cultures.
    Thanks for the info.
    Does it matter if I freeze it immediately or can I wait a few days?

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  7. Jonesy,

    As long as your starter has the two cultures I mentioned, it doesn't matter which brand. I have been freezing it within a few days of making the new batch, and it has been working fine. I am up to batch #9, and still going.

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  8. Please advise as to exactly how you've been freezing the 2-3 tablespoons of yogurt culture. And do you just throw it in frozen when you're making a new batch? And also, what is the tip with the whisk?

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  9. Marge,

    I put it in a small tupperware container before putting it into the freezer. For the next batch, it needs to thaw entirely in the fridge, or be thawed in a warm water bath right before using it. Do not heat it up to thaw it out, and don't put it in frozen. Just chilled like it would be if it were fresh. I don't use a whisk when making yogurt, and could not say what the tip is.

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  10. I think a small glass jar with good lid would work, too, for freezing and thawing as you recommend. What do you think? Thanks for the great stuff here. I am officially a yogurt maker thanks to my friend Sue who introduced me to this and your site has been great. I bought the heating pad and thermometer! No more buying organic FF yogurt. I now buy a gallon of organic FF milk for $4.59 and get 4 quarts of organic yogurt from that. The last container of Stonyfield organic was $4.19. And it's so easy!!

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  11. Marge,

    As long as it is tempered (so it doesn't crack), I think glass would be fine. As far as the cost savings goes, there really is no comparison. The value-added markup on yogurt is astronomical. If more consumers would wise up, they'd find that they would not only save money and reduce packaging waste, but that they can make better yogurt at home.

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  12. With you all the way, Mr. Homemade Yogurt guy, on reducing packaging waste and not throwing my money down the drain. And eating a lot more yogurt as a result. I'm hoping my next bone density test shows it, too!

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  13. I have been freezing food in glass jars for 50 years, and the key is just to leave an inch of headroom--any kind of jar works just fine and I never have breakage unless I drop it!

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  14. I think these bacteria could also metabolize sugar aside from lactose, so you supplement your culture with sugar you'll probably be able to keep them going for longer period but you need to do more research on this

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  15. It doesn't sound like a whole lot of yogurt to me! I have eight kids and a half gallon of yogurt is *one* breakfast for us, if we have just that with fruit and some granola on top. We have yogurt for breakfast once a week, so a half gallon every seven days is easy to maintain!

    Interesting about the bacteria using up their food. I had the same question about the yeast in sourdough and the issue was the same. Now that I make bread once a week from my starter, I never have a starter fail to do its job. I guess yeast and bacteria are like all living things: they need food to survive!

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  16. Great blog!....i am a newbie in Mexico where yogurt is not a forte..It is eaten a lot but not at all like Fage. I started this first batch with a mix of goat milk pro biotic and a good organic. Any suggestions for getting the perfect Fage taste....it is not sold here.

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  17. I don't have any advice for you, Linda, but I just wanted to pop in and say that as long as my milk cools to 110 and the bath water is 110 and the heating pad is plugged in, I'm making one successful quart of NF organic yogurt after another. I make shakes: 1C yogurt, 1C blueberries, 1/2 of Naked mango puree, a splash of almond milk (high in calcium and nice aroma), a heaping teaspoon of fig marmalade for sweetener, and a tablespoon of psyllium, which makes it pudding-like and needs to be eaten with a spoon. DELISH and filling!

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  18. I have been using the same starter from previous batches for some time. I think the secret is to get it from a fresh batch and use sterile utensils, then freeze. Have been making 1/2 gallon per week for some time and then strain through paper coffee filters to convert to Greek style yogurt and it always turns out perfect.

    Instead of the heating pad I use a thermoelectric cooler/heater which will keep food hot up to 120° and set it to 115. Stay healthy everyone.

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  19. good tip, thanks. How do you make it stay thick?

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  20. SIka, when you say "stay thick," are you asking about after it's been refrigerated?

    As far as creating thick yogurt, I find that the longer I let it sit in the warmed bath water the better. I've had it in there 12 hours. It's thick when I take it out and gets thicker after refrigerated. If not bathed long enough, it's loose-ish when first putting it in fridge. So I give it a long time.

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  21. My culture seems to peter out after about nine uses... how long did your's last?

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  22. M.K., when you say your culture peters out, do you mean that you have a failure and no yogurt but just warm milk? And then you're forced to buy store-bought yogurt or get some from a friend for your new culture? I haven't counted but I'm going strong and it feels like I've made many quarts. Not sure. I'll start keeping track.

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  23. Enjoyed your blog. Reminded me of a poem I wrote in 1971, namely:

    At Least With Yogurt There Is Hope

    Bacteria Bulgarius in its Garden of Eden
    Goes dividin’ along at a rate nearly speedin’
    Asymptotically approaching its end without care
    That its source of resources is approaching threadbare.
    They slow their digestion of gluttonous haste
    Only when there’s no more food to taste.
    But Bacteria Bulgarius are lucky, for when they reach such a fix
    They just lie back, go dormant, and wait for fresh mix.

    [22 January 1971.
    Motivated by a gift from Carl Spiroff, a friend at work, of a live bacteria culture, which, he said, was over a thousand years old.]

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  24. Hahaha, that is the cutest poem ever!! Thank you for sharing! So far I'm getting great yogurt (judging by thickness only), so I'll wait for a failure and then reboil/let cool the failure and add fresh culture!! I should estimate how many I'm on now and keep track. Happy yogurting!!

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  25. I just tried your way of yogurt making and i just realize that i think i had too much starter.
    What will happen? Is it going to finish off faster or be even more sour.
    I live in Romania at the moment so i don't have these fancy starter. so I'm trying a local brand with pro-bio things in it and 3.5% fat milk.
    I'm looking forward to see the result.
    Cheers

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  26. ApieceofJonte,

    I don't think putting too much culture in is going to speed it up. Only time will tell of course. Write back and let me know.

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  27. I put 2 qts 1% milk in crock pot on low for 2½ hrs (you can use whatever % milk you choose). After the 2½ hrs, turn off & let sit for 3 hrs. After 3 hrs, whisk the warm milk mixture, take out 2 cups & whisk in your yogurt starter (your preference - I save ½ cup from each new batch to use as starter for the next batch). Wrap the crock in a towel & put in a thermal bag for 12 hrs. Whisk & pour into a cloth lined sieve/strainer. Wash out crock & carefully sit the strainer full of mixture on top the crock to strain. Place plate on top & sit in refrigerator for 8 hrs. All the whey will drain out & can be used separately (google for uses). You will then have a very thick, wonderful yogurt. I whisk mine again, reserve the ½ cup starter in a separate container & refrigerate all. It is WONDERFUL. Makes 1 qt.

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    1. Hello Mimi. Is a crock pot a "slow cooker"?

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  28. Marmalady,

    Yes, Crock Pot is a brand name for a slow cooker.

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  29. HI THERE, DO YOU HAVE A RECIPE FOR 1L OF MILK, I AM A SINGLE WOMAN AND I COULD NEVER USE THAT MUCH YOGURT AT ONCE:(
    IF YOU COULD TELL ME HOW MUCH STARTER TO USE.... HEY THANKS AND KEEP UP THE GOOD WORK. IT IS PEOPLE LIKE YOU AND YOUR READERS THAT ARE SECURING THE MENTAL AND PHYSICAL HEALTH OF FUTURE GENERATIONS... BLESS YOUR HEART!

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    1. 1 liter = 1.056 quarts so just halve the recipe that calls for 2 quarts. I buy the frozen, dried starter & use 1 packet per qt, so for 1 liter use 1 packet.

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  30. This comment has been removed by a blog administrator.

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  31. Does it matter how long the milk sits after is cooled before you add starter and begin to make the yogurt? Thank you

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    1. This comment has been removed by the author.

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  32. If it goes down below 110 degrees, you have to reheat it.

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  33. My yogurt is coming out great. The milk is 110 degrees and the bath water is 110 degrees. And the pot sits on a heating pad to keep it at whatever temp it ends up 12 hours later. Yes, I'm doing 12 hours and sometimes more. The more it sits there, the thicker it gets. I started it today at 3 p.m. maybe and I might not take it out and refrigerate it until I wake up tomorrow morning!

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    1. marge201, how do I get to your original post on making your yogurt? I'm interested in the bath water & heating pad instructions. I'd love to make more yogurt for the effort since I have to strain mine to get it thick. Thx

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    2. Mimi,

      The original tutorial is here:

      http://www.makeyourownyogurt.com/

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  34. I don't strain the yogurt. I use it solely for yogurt shakes/smoothies/lassis and don't want to lose the nutrition of the whey. I use psyllium, which converts the shake to pudding. It's fantastic. Learned about it from Dr. Oz. I learned how to make yogurt from a friend but then finessed and perfected it right here. TY so much, Mr. Homemade Yogurt! My yogurt is very very tart, way too tart to even think about eating plain. Maybe it's that tart because I let it "cook" so long???

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  35. When the boiled milk cools down to 110, I put a few tablespoons of it in the small jar that has the starter, shake it good, pour it back into the 4-cup pyrex mixing bowl, mix with a clean spoon, and pour into my 4-cup glass jar. Put that it into the 110-degree water that's sitting on top of the heating pad, cover pot and wrap with big towel. I make 2 to 3 quarts a week for myself. Love it!

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  36. Thx so much! Since I've already started mine in the crock pot today, I think I'll try the heating pad when I get to the step where mine sits in the thermal bag wrapped in a towel & see how that works. I wondered how constant the heat stayed & how low it dropped sitting there. This should be more accurate. I hated pouring all the whey away & only ending up with a quart from the original 2 qts of milk. Will try your whole procedure next time. :)

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  37. I finally tested the "bath" water today. It started at 110 degrees at about 3 p.m. on May 23. I left it in there until 8 a.m. on May 24. Very thick. VERY TART. But like I said before, I don't care because I make smoothies. I'm wondering if all that multiplied bacteria in there that made it so thick is healthier. Does anyone know?

    Anyway, the water was 110 degrees at 8 a.m.! So the heating pad does keep the water steady at 110. I was surprised. I use a large pasta pot (the type that times with one of those removable steamers). I'm surprised that the heating pad can penetrate so well the metal pot to keep the water at 110 but the thermometer speaks the truth here!

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  38. Put mine on the heating pad (in the crock pot) at 7:30 pm. It was quiet thick at 1 am this morn. At 6:30 this morn it was thinner but I've put it in the frig to see what happens. I can always drink it. :) Will put it in the frig earlier 'next' time. The heating pad held it at 114°.

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  39. Very odd that it thinned out after 1 a.m. Don't understand that. I'll have to ask my yogurt guru about that (unless Mr. Make Your Own Yogurt, who I owe my yogurt to with this marvelous blog, steps in here with an idea). Maybe 114 is too hot and killed the culture?

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    1. I heat mine in a crockpot with a digital thermometer in it and keep it between 110 and 120 and it turns out perfect every time. Takes 5 hours tops too. No more. I also use 100 percent nonfat powdered milk every time adding a little extra milk powder than what is called for. Thick like Greek yogurt every time too. If you use cheese cloth and strain it you can use in place of cream cheese even in baked cheese cake recipes.

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  40. Maybe 114 is too hot and killed the culture? Why would it thin out after it had gotten quite thick? Maybe the heating pad somehow or other got hotter after it got thick and then killed it off? If I had checked and saw quite thick, I'd have figured that's enough and put it in fridge.

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  41. 114 F is not hot enough to kill the culture, and it should have just kept on going. However, if it got hot (let's 130 or 140), it would be the same thing as cooking some store bought yogurt. In other words, it would get runny. Not because the cultures died, per se, but because heat breaks down the curds. I never leave my yogurt more than 7-8 hours. It's way too tart after that, for my taste, so I really couldn't say what goes on after an all nighter.

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  42. I appreciate your comments, Mr. Homemade-Yogurt! Yes, it is really tart but my smoothies still come out great. Do you think that it's any healthier leaving it overnight? The bacteria keep multiplying. Right? Is there a health benefit to that? The yogurt is thicker and tarter the longer it goes. Or does it hit a wall with thickness and just keeps getting more tart?

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  43. Please call me Michael. Obviously you have a preference for tartness, so you should do what you like best. But at some point, there is no lactose really left in the milk, and it has been converted to lactic acid (the tartness). Is this more healthy for you? I don't know. If you have lactose intolerance, then it may allow you to enjoy some dairy. But beyond that, I really couldn't say.

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  44. Hi Michael! Thanks so much for your wonderful blog and this opportunity to understand the process even more. No, I don't have a preference for tart at all but I do like it thick. I only recently connected the extra long "cooking" time with extra tartness. I don't have lactose intolerance but I do need the calcium for the bones. Sounds like I'll be sticking to your 7-8 hours in the future.

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  45. Perhaps adding some non-fat dry milk (1/4 c. per 1/2 gal. warmed milk) when adding the starter might help thicken it without incubating for more than 7-8 hrs. I will be trying this with a batch next weekend.

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  46. My last batch was 8 hours and it was very thick. So no more 16 hours for me. All you get from that, I see now, is tart. I add 1/2 C NF dry milk to 4C skim milk to up the calcium. I've got a batch cooling down to 110 right now!

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  47. Thank you for this great blog!! This might be a stupid question, but can you Kefir for the starter? I know Kefir has for more "good" bacteria that most yogurts. I also have a Euro Cuisine yogurt maker. Has anyone else used one? Thank you again.

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  48. Great question about using kefir as starter. looking forward to reading any feedback.

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  49. As far as I know, you can make kefir using the same process I describe on my yogurt website. But i do not know if you can start with store-bought kefir as your culture. I've never made nor had kefir myself, so I could not say.

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  50. A couple of times you mention "reserve 2-3 Tbs. of it to start your next batch," but do not say how large your batch is? one gallon? one cup? please?

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  51. Happy fourth of July!
    I have a few questions:

    ** In September of 2011, you started a batch of yogurt with Dannon Plain Yogurt, containing Lactobacillus bulgaricus and Streptococcus thermophilus
    ** How long did you keep / have you kept that batch going? (# of batches and last date successfully done)
    ** What was the largest batch of milk used and how much starter did you use in this batch?
    ** When you save back starter, do you freeze it ASAP?
    ** How long have you successfully frozen held back starter?
    ** If that September batch is no longer being reused, do you have an explanation for what stopped you from holding starter back and reusing from that batch anymore?

    I tried Cultures for Health Bulgarian starter, but the freeze-dried culture was 1/4 teaspoon for the entire order and even though I've made countless gallons of home made yogurt, there's was a hit-miss proposition. I had a new box of their culture, got it in January / February 2012... and was a backup. Well... got back from vacation and made mistakes with the re-used starter and poof! All that money down the drain.

    So I went to the freezer for the backup box of culture and it just did not work. TOTALLY $disappointed with their product, even though their customer support was outstanding.

    So am looking for another more $practical$ method that is lower cost to start with and more human fault tolerent!!!

    Thank you.
    Clinton

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    1. I make 1/2 gallon at a time, and I kept that experiment going for 12 batches. I don't recall over how long a time period, but it was at least 12 weeks, probably more like 16. During that experiment, I did find that freezing the 2-3 Tbs., right away (right after a new batch was done) was the way to go. Then defrost it in the fridge the night before you are going to make your next batch. It worked without fail. We had a prolonged power outage where I live, and I tossed the culture rather than risk having it not work.

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    2. Wow... that is excellent news to hear.

      I am surprised at how little starter you hold back. Not complaining, but pleasantly surprised!

      I am guessing that freezing the next batch's starter ASAP would keep it most active / potent for the next batch.

      It also gives you some flexibility in case you would be away for a week, for example... that held back starter will / should stay good.

      I was just trying to time it, meaning I would keep it in the refrigerator, but try to make a new batch between 10 and 14 days from the last. It worked... except when I froze 14 day old starter. When I came back from my trip, it had no kick and did not get the job done.

      OK... it's time to pick up some Dannon Plain Yogurt!

      THANK YOU!

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  52. Great blog - thanks! I've been making yogurt in my crock pot every week for several months. I use 2 litres of UHT milk. It's cheap here (Costa Rica) and it avoids the process of having to heat it to high temperatures and waiting for it to cool to 110F. I put the milk in the crock pot and set it for 40 min and then add starter. I then wrap the crock pot in insulation and put the whole thing in a insulated cooler around 4pm. By 7am the next morning it's perfect for my taste! I use at least 1 cup every morning with breakfast. I was saving a little bit from the previous batch as a starter and it was still going strong, but I read that you should re-start with commercial yogurt every once in awhile so I did that. I see now that was a mistake. I should have just kept it going. Next I'm going to try to make my own starter. I know it sounds weird, but I read you can use ant eggs, anthill dirt, goat dung or red pepper stems. The first natural yogurt had to come from somewhere - right?

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  53. Great Blog Michael,
    I have tried several methods from other online sites with average results. I enjoy knowing what I am doing when yogurt making so your scientific approach really helped my confidence. Just made my first batch with fantastic results, much creamier and astonishingly less tartness than my other attempts - I enjoyed it plain - that's a first for me!
    Many many thanks for your efforts in creating this blog.
    Sorry to hear you had the power outage. Even if it is insured, there is something disturbing about throwing away once good food like that isn't there?
    Any thoughts on using pre-boiled kettle water that's cooled enough and powdered full cream milk? Is there any difference in the lactose that would affect the process? (I just figured there is wasted energy in the boiled water from my cuppa I could reuse. And... it's easier too!!)
    Thanks again for your site and this blog they are a real help.
    Regards, Elton

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  54. Thanks for this info -- good to know, since I've just started making yogurt in the crockpot, and have read that before, about the starter only lasting a few times. I've just made the first of my 4th generation batch. I started with Fage yogurt, which has five bacteria including the two you mentioned.

    I strain out the whey for about an hour -- about 2 cups for every half gallon of whole milk -- and use the whey instead of water for cooking rice or making rolls. When the yogurt batch is strained and cooled, later that same day, I set aside and freeze a half cup for the next starter, then thaw it in the fridge about 12 hours before it's needed for the next batch. I have more starter for the 4th generation, but will hit the 5th generation version soon. So it sounds like I shouldn't have any problem with later generations of the starter, since I've done it this way.

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    1. Please keep us informed. I hope you are right, but I would not assume that the Lactobacillus bulgaricus and Streptococcus thermophilus strains found in Dannon plain yogurt work the same as the combination of the five strains in Fage.

      I hope you are correct. Please keep us informed. There are enough variables (percentages, adverse reactions of additional strains, etc.) that I stick with the Dannon Plain as my base. It's also available here in case my starter stops.

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    2. Lynda,

      Per SunMan's comment, I would not automatically assume that all five cultures from the Fage are transferring to the final product, just because you obtained a good result.

      The process I am using is optimized for L. bulgaricus and S. thermophilus, which grow optimally at 100-115 F degrees, whereas L. acidophilus and L. Casei (both in Fage) do best at about 90 - 105 F degrees. So if you are adding the starter at 110 and keeping it thereabouts for the incubation period, you are likely not getting much of the latter two. If you lower the temperature to optimize for them, you'll miss the target range for the former. I am not a scientist of any kind, and I suspect having someone trained look at it under a microscope is the only way to really know. But my gut tells me you are likely getting L. bulgaricus and S. thermophilus, which are both classic yogurt making strains that work synergistically to convert the lactose.

      So how does Fage do it? Again I am not really qualified to answer, but they may start the process at 110-115 using just the first two cultures. After a specific amount of time, and substantial amount of culture production, they could lower the temperature and add the others. These cultures are acid-loving, so putting them after the yogurt is already partially completed would not be out of the question. But who knows. Anyone?

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    3. I searched online for more info regarding the other three cultures in Fage. Yes, I suspect that is the case, too, that after the first few batches (I'm still eating from the third batch, but the fourth batch looks the same quality) I'll only have the two strains that are also in the Dannon yogurt. Didn't know that about the lower temp range for the other strains, and yes, I'm doing the range of 110-115, below 120 F.

      I'm still hoping that the two strains will continue for many generations, same as what you describe above. In a few weeks I'll know. From comments above and elsewhere, I guess what happens after a few generations of the direct set cultures is that after the incubation period, the milk is still warm milk... in which case would have to run to the store to get a new starter.

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    4. When I started the homemade yogurt about a month ago, I didn't know which particular store-bought yogurts were best for starters. Aldi's regular yogurt was a much larger quantity with only one or two cultures, but Aldi was also selling a smaller container size of Fage at a good price, so I just picked that.

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  56. I just found your website a few days ago, went out and purchased a small quantity of plain yoghurt and proper thermometer and made my first batch of yoghurt yesterday! Wow, it's delicious!! Thank you so much for your website and blog! I was "terrified" of doing anything wrong; I didn't even check the temperature as it was "cooking" for the seven hours, but I did feel the outside of the pot which seemed quite warm and lowered the temperature on the heating pad to "low". Next time, I'll check the temperature...lol! I guess I'll know for sure whether or not the temperature was too hot if my reserved starter doesn't work. The only change I made was to whisk it after the "cooking" period. I was a little busy in the kitchen at that time, trying to serve dinner and wanted to get the yoghurt in the fridge as quickly as possible. Once again thank you and Happy Yoghurt Making!!

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  57. One time I measured my 110-degree bath water when the yogurt was ready to go in the refrigerator after spending the whole time on the heating pad at high and the pot covered with a large towel. The water was 110! I haven't had a failure since I'm strictly at 110 for the milk and 110 for the water. Using a few teaspoons of yogurt from new batch as starter for many months now. Don't see it wearing out!

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  58. This is the thermometer that I use and I love it.
    "Maverick ET-71OS RediChek Remote Wireless Cooking Thermometer With LCD Transmitter"

    http://www.amazon.com/Maverick-ET-71OS-RediChek-Thermometer-Transmitter/dp/B000ZM7M0O/ref=wl_it_dp_o_pdT1_nS_nC?ie=UTF8&colid=CUZ5H1IQOFO5&coliid=I1GW97UVXHIGBN

    It's incredibly cost effective, accurate and super versatile. The stainless steel braided wire that leads to the sensor makes it very durable.

    Wouldn't be without it.

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  60. FYI, after I put my newly made yogurt into quart mason jars and tighten the lids, I place them in a playmate cooler, then fill it 1/2 to 3/4 way up with very hot tap water, then close the lid and leave over night. I've never had a batch fail on me that way.

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  61. Can you clarify the amount of existing yogurt that it takes to make a new batch? You say 2-3 tbs but for how much milk? Thanks!

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    1. The recipe is for a 1/2 gallon. I am sure it would work for a gallon, but it wouldn't hurt anything to double the starter if you are doubling the milk. The key is to get fresh starter. Freezing some right away is the key; or buying new yogurt from the store.

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  62. I fill a 32-ounce glass jar almost to the top with skim milk. Need room for 1/2 cup of NF dry milk powder and 2-3 tablespoon of starter, which is fresh yogurt from my last batch. BTW, I love Michael's digital book. Everyone should support this guy. He's saved me a lot of money by making my own yogurt!! http://www.amazon.com/How-to-Make-Yogurt-ebook/dp/B00BEJS9S6/ref=sr_1_4?s=books&ie=UTF8&qid=1360864671&sr=1-4&keywords=how+to+make+yogurt

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    Replies
    1. Not exactly a scientific way of doing yogurt, but since I was lacking what I needed at the time, I find it interesting that a bean bag worked: I made a batch of yogurt and brought it down to 100 degrees. By using a small, well insulated cooler and inserting the 1/2 gallon jar with yogurt and a homemade bean bag (like you'd use to heat and put on sour muscles or neck) heated in the microwave to about 130 degrees. Since the cooler was not preheated I thought I'd try this temp. NOTE: I didn't allow the hot bean bag to touch the jar and I put a dish towel on top of the jar to help hold in the heat. Ten hours later I had great yogurt.

      I don't have a Kindle nor do I know a thing about them. Can I download Michael's ebook and read it on my computer? Sounds like a great resource to have.

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  63. I am new at this (only made 3 batches so far) and all this information has been very helpful so thank you for that! I was wondering if I needed to strain the whey out of my homemade yogurt when using it as starter for my next batch or does it not matter? I should point out that I do strain the whey for regular consumption. Also, will yogurt that is a little watery still work as a starter for another batch? Thanks in advance for any help/info!

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    1. I don't strain my yogurt at all. I just mix the whey back in, if any forms. I suspect that when you strain it, some of the cultures go with it. As far as a runny starter working, it depends on why it is runny. If you follow the tutorial, you should not be making runny yogurt. It should be more or less like Stoneyfield or Dannon. The culture that you freeze will be runny when you dethaw it. But the yogurt you are making should not be runny. Does that make sense?

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    2. Yes, it does. Thank you very much. As for runny yogurt, I feel like I have a lot of whey in mine and that might be why it doesn't look thick. I will be sure to keep they whey in it as I will be using this for my starter. Thanks again!

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  64. Thanks everyone for all the useful information.

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  65. I'm really new at this. We've eaten all but one remaining glass jar of homemade yogurt. It has been sitting in the fridge for about 12 days. I ate the second to last jar yesterday and it was delicious, just only a little sour, no liquid on top. Is it okay to use this 12-day-old yogurt from the last batch to start a new one (it will be the third batch from same cultures)? Can I use the whole jar or only 3 tbsp? Thanks for your advice! Next time I will freeze one jar to save as my starter.

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    Replies
    1. I wouldn't use it. It's fine to eat, but is probably too weak as a starter. Buy some fresh store bought, and get in the habit of freezing some starter right after a new batch is made.

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    2. Thank you for your quick reply! May I ask, what is the risk of a "weak starter"? What is the impact on the yogurt? On the consistency, the nutritional value, the number of cultures, the taste, etc? How would one detect the difference in quality of homemade yogurt? Thanks!

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    3. The impact can range from it not coagulating at all, to just runny yogurt with little flavor. And if there is no measurable "good" bacterial activity, you have left a pot of warm milk sitting out for hours, opening the door for "bad" bacteria.

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    4. Homemade-Yogurt is 100% correct.

      1) Go buy some Dannon Plain Yogurt.
      2) Use that as starter.
      3) Strain off whey from starter (no need to freeze/store whey.)
      4) When I use a gallon of milk to make yogurt, I save about 1 cup and freeze it.
      5) Doing this on the front end (immediately after making the yogurt) gives you vibrant starter that will freeze just fine for a few months without degrading the strength of the starter.

      Good luck and enjoy!

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  66. So I had a situation where I was not able to make yogurt for a number of months.
    1) In August of 2013, I made a batch using the starter purchased a couple years ago as Dannon Plain Yogurt.
    2) I held back about 1.5 to 2 cups (out of a gallon) for starter and immediately froze it in a plastic sealed lid container (Tupperware).
    3) Now in February 2014, I thawed the starter out and used it to make a perfect batch of yogurt with one gallon of skim milk.

    So I'm sure I've used this same strain of starter a dozen times and in my opinion, it gets more and more smooth over time.

    Plus I froze the held back starter for at least 5 months successfully.

    Works great!

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  67. I use a soft-sided thermal bag to incubate my yogurt. I attach a 15 watt lightbulb (with a screw-in socket) to an extension cord. I set the lightbulb upside-down into a coffee mug inside the thermos bag and this will keep the interior at a steady 105-110F degrees. Use an instant-read thermometer (place tip inside incubator, with the dial poking out of thermal bag)- zipping the bag nearly tight - like zipping up a small travel bag. You can control the interior temperature by opening the zipper a bit if the temp is too warm, and/or lifting the bulb higher in the coffee mug if it's too cool (to expose more of the bulb's heat). I use a large paper clamp or food bag clamp to grip the extension cord where it goes inside the thermal bag, and this makes it easy to raise or lower the lightbulb in the mug. Anyway, I use a 1 gallon Pampered Chef tempered glass measuring bowl with the lid on during the incubation. I can heat this container in a pot of hot water (place a dishcloth in the pan for the bowl to sit on. Then bring the water to a boil. Use a candy thermometer to check your milk temperature. Once you reach temperature, just move the bowl (use hot pads) from the heat to add your yogurt starter. Works every time.

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