The Science of Great Yogurt

Our yogurt method is based on the principles in Harold McGee’s On Food and Cooking, and on the research by professors W.J. Lee and J. A. Lucey from University of Wisconsin-Madison on commercial yogurt making methods.  These sources pointed out two important concepts for creating thick, creamy yogurt:  holding milk at 195 ºF / 90 ºC for ten minutes before culturing, and allowing the yogurt to set at a lower temperature.

Note: When using the Folding Proofer to make yogurt, be certain there is no water in the water tray. The water tray is not needed for making yogurt.  You can remove it from the Proofer, if you like, or leave it empty. But do not add water because it will affect temperature settings.

homemade greek yogurtFor a Thick, Custard-Style Yogurt, Choose a Higher Initial Milk Temperature.  Standard methods for making yogurt call for the milk to be heated and cooled before culturing, and different temperatures create different styles of yogurt. Yogurt made from milk kept below 170 ºF  / 77 ºC is thinner and tastes fresh, a little fruity and more tart, while yogurt made from milk held at 195 ºF / 90 ºC for 10 minutes is noticeably thicker and tastes less tart and somewhat creamy/nutty/eggy.

Protein is Key to Thickening. The more protein in milk, the thicker the yogurt. The casein (protein) clusters in milk thicken yogurt by unraveling and forming a three-dimensional mesh when exposed to the lactic acid created by culturing. Heating milk before culturing denatures one of the main whey proteins, lactoglobulin, which allows it to join in the mesh (instead of remaining inactive) and effectively increases the amount of protein in the milk that will be available to thicken the yogurt. The milk needs to be held at 195 ºF / 90 ºC for ten minutes to denature most of the lactoglobulin. A little evaporation during this heating also aids the thickening benefits of this procedure. When available, higher-protein, richer milks like Jersey or Guernsey make wonderful yogurt.

Does Boiling before Culturing Ruin the Yogurt?  No.  The milk will not curdle when boiled unless acid is also present, and the integrity of the fat in milk is actually strengthened by boiling. To test this, we made yogurt from milk that had been simmered long enough to reduce the volume by 25%. The result is a thick, smooth and creamy yogurt with the strongest “custard” taste of any of the yogurts we tested. We didn’t choose this method for our custard-style yogurt because the cooked milk/custard taste is so prominent that it starts to seem like something other than yogurt. But it was a favorite among some of our tasters, and it’s good to know that if you accidentally heat the milk hot enough to produce a few bubbles, nothing bad will happen to your yogurt.

Lower Temperatures Give a Better Set.  In addition to the quantity of protein available to form a mesh, the stability of that mesh is also important. That stability is determined by the temperature at which the protein mesh forms, i.e., the temperature of the yogurt when it sets. The yogurt will be smoother and more stable (less likely to leak whey) when it sets at a temperature below 104 ºF / 40 ºC.  Being able to turn down the temperature during culturing is a key benefit of using the Proofer, a benefit which allows the smoothest, best texture to form (see texture comparison in photo of spoons, below).

High-Low yogurt method makes smoother yogurt (left spoon) than hot culturing (right spoon).

High-Low yogurt method makes smoother yogurt (left spoon) than hot culturing (right spoon).

Low Temperature Cultures can be Slow.  Harold McGee points out that commercial yogurt is sometimes cultured at 86 ºF / 30 ºC, and that a lower culturing temperature ensures a smooth yogurt with less risk of whey separation. Higher temperatures and longer culturing times can cause a lumpy texture and excessive whey separation (similar to the spoon on right on the photo).  We tested an 86 ºF / 30 ºC culture and found that it makes perfect, smooth yogurt.  However, a temperature that low takes a very long time (12-18 hours) and made us a little uneasy about food safety.

Our “High-Low” culturing method produces smooth, thick yogurt that is less likely to leak whey, yet is much more quick and safe than a low-temperature culture. We start the culture at 120 ºF / 49 ºC, a temperature that speeds the yogurt through the earlier stages of culturing.  Then as culturing progresses and the rising acidity begins to inhibit any potentially problematic microbes, we turn down the Proofer to 86 ºF / 30 ºC. The method works well, and culturing takes just 2-4 hours, not 12.

Which Culture? Our testing showed that store-bought yogurts are not all created equal- some made better starter cultures than others. While all the brands of “live culture” supermarket yogurt worked, some produced thinner textures while others made thicker textures. Yogurt cultures that included L. Casei tended to have more viscosity and set up faster than those that didn’t. Some of our tasters loved the more viscous texture but some didn’t. A culture containing only the two classic yogurt microbes L. Bulgaricus and S. Thermophilus had very little viscosity. We also had the best luck with smaller (8 oz / 250 ml) containers. Even within the same brand, starter yogurt from 8 oz containers tended to produce smoother yogurts than larger economy tubs, possibly due to faster turnover and fresher cultures. It’s worthwhile to test a few different brands of yogurt until you find a favorite.

homemade yogurt with fruitSweeten after Chilling.  If sweeteners are needed, we like to add them after the yogurt is set and chilled. We prefer not to add sugar before culturing to avoid feeding any undesirable bacteria. The beneficial lactic-acid producing flora are naturally well-equipped to feed on lactose, while other less desirable bacteria are not. Adding non-lactose sugars to the milk could feed any undesirable bacteria that accidentally end up in the milk through equipment or inadequate heating. As the culture progresses these will be inhibited by lactic acid, but we prefer to avoid growing undesirable bacteria on non-lactose sugars during the early stages of culturing. Honey, due to its anti-bacterial qualities, can slow down culturing and so is best added just before eating.

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2017-03-09T19:56:31+00:00 Yogurt & Dairy|19 Comments

19 Comments

  1. jbanks February 9, 2016 at 3:42 pm - Reply

    In your high-low method you mention the process takes 2-4 hours, but you don’t say how long you hold it at 120 before turning it down to 86.

    • Diane February 9, 2016 at 5:00 pm - Reply

      Thank you for your interest and comment. You can find the complete instructions in our Custard-Style Yogurt recipe. 120 degrees is for 1 hour and is part of Step 4 in the instructions. This recipe is a favorite of many customers.

  2. Brookiescc May 13, 2016 at 7:38 pm - Reply

    Thanks so much for your information. It was so clear and detailed. I have one additional question. With the protein becoming more usable as we heat the milk (the mesh I believe you called it), is this what accounts for the increase in protein on the nutritional info. I make greek style yogurt at home and have always wondered how there could be more protein per serving than in the milk itself that was used to make it. Thanks for the explanation.

    • rkamp May 16, 2016 at 4:29 pm - Reply

      The reason that Greek-Style yogurt has more protein is because the proteins become more concentrated when the whey is removed. So the same amount of Greek-Style yogurt has more protein than an equivalent amount of yogurt that has not been strained.

  3. Emma September 8, 2016 at 2:35 am - Reply

    I can’t get the milk above 180 degrees in my double boiler, which I use to avoid scorching the milk. If I hold the milk at 180 for half an hour, does it have the same effect as 10 mins at 195?

    • Diane September 8, 2016 at 3:20 pm - Reply

      Heating the milk before culturing determines part of the flavor and how thick the yogurt will be. If you just heat the milk to 165F briefly and then cool, the yogurt will taste fresh, a little fruity, and will be thinner and more tart when it sets. We have not tried 180F for one half hour so we can not say for sure whether that will work but have doubt. If you heat the milk to 195F and hold it there for ten minutes, the yogurt will be milder and thicker when it sets, and will have a bit more of a cooked milk taste. Holding the milk at 195F for ten minutes is certainly optional. It helps produce a thicker and slightly milder yogurt. The process at 195F denatures whey proteins, allowing them to contribute to the solidification of the yogurt. And with the extra protein the yogurt sets a little earlier in the culturing process, so that the flavor can be mild, or the yogurt can culture longer if more tartness is desired. Hope this answers your question and best of luck with your yogurt making.

  4. Brett Bauer February 1, 2017 at 9:38 pm - Reply

    Any thoughts on how to incorporate Lactobacillus reuteri into a yogurt?

    • Diane February 8, 2017 at 3:43 pm - Reply

      Brett, This is a very good question. We are not certain where you can purchase a starter to introduce Lactobacillus reuteri into homemade yogurt. We have read that when this bacteria is introduced it will likely result in a more sour yogurt and can produce a more slimy consistency. Stoneyfield Farms, one company which produces a variety of yogurts, used to include Lactobacillus reuteri in their yogurt products but we read that they eliminated this particular bacteria due to customer dissatisfaction with the sour taste. We have not found another source for you but if we find any further information we will follow up with you.

    • Petr September 22, 2018 at 1:23 pm - Reply

      L. reuteri is included in Nature’s Way, Primadophilus, Reuteri Superior Probiotic powder. It includes Lactobacillus reuteri, L. acidophilus, Bifidobacterium longum, L. rhamnosus. I use that powder as a starter culture. It takes longer than using yougurt as a starter culture.
      You can use other L. reuteri pill or powder as a starter culture.

      The resulting yogurt tastes best at not too thick stage, later it starts to get thicker and sour and even later it tends to get from sour to bitter and the whey starts to separate. I find it best when it just starts to be litle sour. I also found that if I add prebiotic powder to the mix (fructooligosacharides and inulin) it takes longer to get acidic and it is sweeter and may be slightly thicker.

  5. Betsy Seeley August 1, 2017 at 12:58 am - Reply

    How are you holding your yogurt at 120 for an hour and then 86 for the remainder? In oven with light, or wrapped in a towel or in the instant pot?

    • Diane August 2, 2017 at 3:14 pm - Reply

      Betsy, Thank you for your interest and question. We hold the temperature with the degree-by-degree settings on the Proofer. We set the temperature at 120F for 1 hour and then set the temperature at 86F for the remainder until the yogurt is set, generally 3-4 hours depending on the milk and culture used. We never use an oven, wrapping towels, or a pressure cooker. The Proofer has reliable and repeatable results. https://brodandtaylor.com/folding-proofer-get-inspired/ All the best to you in cooking and baking.

  6. Anne November 28, 2017 at 4:10 am - Reply

    Hello. Thank you for the very informative site. I am wondering why, as you say, yogurt ferment with lactobacillus casei turns out thicker. I have noticed this myself in my own yogurt making and am trying to research what characteristics of l. casei cause this effect. Thank you for any further insight you can provide.

    • Diane November 30, 2017 at 5:01 pm - Reply

      This is a very good question. Through our testing years ago, we noticed our yogurt starter cultures containing Lactobacillus Casei bacterium generally resulted in a thicker and more smooth yogurt. This could in part result from this particular species of Lactobacillus documented to have a wide pH and temperature range. Milk with a higher protein content can also develop a thicker yogurt. Both of these steps help yogurt utilize more of the whey proteins in milk for thickening and stabilizing the texture.

      Heating the milk before culturing also determines how thick the yogurt will be. If you just heat the milk to 165°F briefly and then cool, the yogurt will be thinner and more tart when it sets. If you heat the milk to 195°F and hold it there for ten minutes, the yogurt will be milder and thicker when it sets. The process at 195°F denatures whey proteins in the milk, allowing them to contribute to the solidification of the yogurt.

      For further information regarding L. casei bacterium you can find Harold McGee’s On Food and Cooking and also W.J. Lee and J. A. Lucey’s research on yogurt making methods. All the best to you in yogurt making!

  7. Microfiber Guru March 8, 2018 at 9:32 pm - Reply

    I always bring my milk up to 180° degrees and then culture at 112°. I do strain it after for a super duper thick consistency, but those temps produce a thick and creamy mild yogurt. I use Whole milk and culture via Sous vide. I assume the proofing box works similarly with the ability to set an exact temperature.

    • Diane March 9, 2018 at 3:37 pm - Reply

      Bonnie, Thank you for sharing your experience with making yogurt. Yes, the Proofer is set to an exact temperature for consistent and reliable results. Customers have also used it for Sous vide method too. All the best to you.

  8. Paul March 21, 2018 at 12:12 am - Reply

    I do not have proofer. I use a cooler with a light bulb, a fan and temperature controller. Cooler are well insulated. The temp drop off from 120 to 86 take a long time. What is the temp drop off for a proofer? How does the drop rate effect the final product? Thanks for the write up.

    • Diane March 21, 2018 at 3:27 pm - Reply

      Paul, Thank you for your question. About 6-7 years ago the Proofer was developed to avoid all uncertainties with various homemade methods of proofing or rising bread, making yogurt and many other foods. The recipes for making yogurt on our website were created with the consistent and reliable Proofer settings in mind. All factors of temperature were taken into consideration along with the reliable settings of the Proofer to ensure our recipes would be successful. Many months of carefully calculated testing was done with different variables to assure repeatable and predictable results using our recipes and the Proofer. There are many other homemade ways to try and succeed with the same results but we can not advise you as there are too many varied factors. The temperature of the milk in making yogurt does indeed affect your yogurt results. Our recipe instructions reflect great results when the instructions are followed, using our Proofer. Contents of the milk & starter culture does not change instantly with the change of a digital setting but the temperature change was considered into the final recipes we created. We hope this is helpful. All the best to you.

  9. Kathleen May 3, 2018 at 3:17 pm - Reply

    I use ultrapasteurized milk when making yogurt, as it is the only organic milk I can buy where I live. I read that ultrpasteurized milk is heated to 280 F. Since it has already been heated past 195 F., is it necessary for me to heat it again to that temperature and maintain that temp. for 10 min. for a thicker, creamy yogurt? Thank you.

    • Diane May 4, 2018 at 4:18 pm - Reply

      Kathleen, Yes, it should be reheated to 195 F and then cooled down before inoculating with the live cultures. That is a very good question. All the best to you!

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