Saucepan of steaming milk on a stovetop

Batch Overflowed: Causes and Fixes

ByCraig Brockie Last updated

Which kind of overflow you have

Three different problems get called an overflowed batch. The milk foamed over the pot while you heated it. The jars spilled over in the incubator. Or the yogurt itself rose, bubbled or pushed up its lid.

The first two are messes, and the batch can usually be saved. The third can be a spoilage warning. Work out which one you have before you decide what to do.

The most likely cause: milk boiled over while heating

Most overflows happen at the heating step, because yogurt recipes take milk close to a boil. University of Illinois Extension heats milk slowly to 180 to 185°F, stirring now and then so it does not burn on the bottom, and notes that the milk will start to steam and form small bubbles at the side of the pot. That is your cue to watch it closely.

As milk heats, a thin skin of heat-changed protein and fat forms on its surface (Evans et al., 2017). Push past the target toward a full boil and the milk can rise up and over the rim within moments. The University of Alaska Fairbanks Cooperative Extension is direct about it: heat over low heat, stir, and do not boil.

How to fix it

  1. Take the pot off the heat as soon as it starts to rise. Leaving it on the burner only adds more foam.
  2. Check the temperature. Milk that boiled briefly is still usable. The heating step is meant to kill competing bacteria, as University of Missouri Extension explains, so a little extra heat does not make it unsafe. UAF notes that overheating or boiling can give the yogurt an off flavor.
  3. Skim off the skin. Missouri advises removing any film that forms on top so it does not give the yogurt a bad texture.
  4. Measure what is left. If you lost a lot of milk, scale the starter down. Illinois uses 2 tablespoons of plain yogurt per quart.
  5. Cool before adding starter. Bring the milk down to 108 to 115°F, as Illinois directs, then carry on as normal.
  6. Clean the burner or cooker base once it cools enough to touch, before the milk bakes on.

How to prevent it

  • Use a pot with room to spare. Illinois heats 1 quart of milk in a 2-quart saucepan.
  • Use low to medium heat and stir, as UAF and Illinois advise.
  • Keep a thermometer in the milk and turn off the heat at 180 to 185°F rather than waiting for a boil.
  • Stay at the stove for the last few minutes. For cooker methods, see our Instant Pot yogurt guide.

Jars that spilled over in the incubator

Glass jars of yogurt with space left below the rim

If the mess is around the jars rather than on the stove, the usual causes are simple:

  • Jars filled to the brim. Leave headspace below the rim. The University of Kentucky Extension notes that because no whey is drained off, its recipe yields slightly more yogurt than the milk it starts with.
  • Water bath set too high. Illinois says the warm water in a cooler or slow cooker should come up the sides of the containers but not cover them.
  • Moving full jars. Fill them where they will sit, or move them with a tray.
  • Drips from the lid. Water collecting under a lid can look like an overflow. See condensation dripping into jars.

To fix it, wipe the jars and incubator with hot, soapy water once the batch is done. If bath water got into a jar, throw that jar out, because the water was not clean. Jars that only spilled down their outsides are fine.

When yogurt rises or bubbles: a warning sign

Yogurt that foams, domes up, pushes a lid open or has gas bubbles through it is a different problem. That points to gas being made in the jar, often by yeast. In a study of spoiled commercial yogurts, one yeast grew in plain and fruit yogurts alike, but only the yogurts with added jam swelled with gas, because the yeast fermented the fruit sugars (Wrent et al., 2015).

So if you stirred fruit, jam or honey into the milk before incubating, gas is more likely if contamination gets in. Kentucky Extension advises adding fruit, honey and other flavorings just before serving, because yeasts and molds can otherwise grow even in the fridge. Our strawberry yogurt guide has more on flavoring. For froth without obvious spoilage, see yogurt foamed during culturing.

When to throw the batch out

Throw it out, without tasting it, if any of these apply:

  • It rose, fizzed or filled with bubbles, or it smells yeasty, beery or rotten. University of Guam Extension advises discarding any yogurt with odors other than the clean acidity of fresh yogurt, or with visible signs of microbial growth. See yogurt smells yeasty.
  • Water from a bath got into the jar.
  • Heated milk was forgotten and left at room temperature for more than 2 hours, or 1 hour above 90°F, the limits FoodSafety.gov sets for perishable food.

Related topics

Sources

Craig Brockie is the founder of Ultimate Health Solutions, the company behind Ultimate Gut, and the author of Ultimate Health, The Ultimate Gut Health Guide and The Unlimited Probiotics Guide. After injuries and chronic health problems in his twenties that conventional care didn’t resolve, he began researching health on his own and has studied natural health for 30 years. He is not a medical professional, and his articles are general information, not medical advice.

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