Glass jars of thin homemade plant-based yogurt on a counter

Plant Milk Would Not Thicken: Causes and Fixes

ByCraig Brockie Last updated

The symptom

You held the plant milk warm with a starter for 8 to 12 hours, and it came out pourable, maybe a little tangy, maybe separated. Nothing set.

Dairy yogurt sets because the bacteria turn milk sugar into lactic acid, and the acid makes the milk proteins pull together into a gel (University of Illinois Extension). Most plant milks lack one or both parts: enough protein to build a gel, and a sugar to turn into acid.

Most likely cause: too little protein

USDA FoodData Central lists these values per 100 grams (about 3.5 ounces). Almond, oat and coconut drinks carry a fraction of the protein in cow’s milk; only soy comes close.

MilkProtein (g per 100 g)Sugars (g per 100 g)What to expect
Whole cow’s milk3.155.05, all lactoseSets on its own
Soy milk, unsweetened2.860.41Can set
Oat milk, unsweetened0.802.32Needs a thickener
Almond milk, unsweetened, refrigerated0.66Sucrose 0.04 (total not listed)Needs sugar and a thickener
Coconut milk beverage, sweetened0.212.5Needs a thickener
Coconut milk, canned2.02Not listedFar more fat (21.3 g) than carton coconut

In one lab comparison fermented to the same pH of 4.5, soy yogurt was the firmest, while oat yogurt had a looser structure and the lowest firmness (Wang et al., Food Research International, 2023).

Store-bought plant yogurt is thick for a reason. A review found that none of the commercial products analyzed matched dairy for protein, and that their texture usually comes from additives such as protein extracts, thickeners and emulsifiers; agar and similar gums can stand in for the protein network (Montemurro et al., Foods, 2021).

Second cause: nothing for the bacteria to eat

Yogurt bacteria need sugar to make acid. In dairy that sugar is lactose. USDA lists zero lactose for almond and oat milk, and unsweetened almond milk has almost no sugar of any kind. With little to ferment, the acid never builds, and the pH does not fall below 4.6, where milk takes on a yogurt-like texture (University of Guam Extension).

Soy milk usually works: the same review calls commercial soy milk a good substrate for the standard yogurt bacteria (Montemurro et al., 2021).

How to fix it next time

Saucepan of warm soy milk with a whisk and bowl of starch

A thin batch that smells clean and tangy has fermented; only the texture failed. Drink it or blend it into a smoothie. Longer incubation will not add protein, and heating it with a thickener now would kill the cultures. Build the thickener in from the start:

  1. Pick the milk. Soy gives the best chance of a natural set. For other plant milks, plan on a thickener.
  2. Add food for the culture. If the milk is unsweetened, whisk in about 1 tablespoon of sugar per quart.
  3. Add a thickener, cold. Whisk in tapioca starch, pectin or agar (all common yogurt stabilizers, per University of Guam Extension) following the package amount for a soft gel.
  4. Heat it. Bring it to a gentle simmer, around 190°F, for 2 minutes, stirring. Starch thickens only when heated in liquid, and agar must be heated to dissolve. Soy yogurt research used about 194°F (90°C) (Montemurro et al., 2021).
  5. Cool to 108 to 112°F. Milk that is too hot when the starter goes in will kill it (University of Guam Extension).
  6. Add the starter. Use a dairy-free culture per its directions, or 2 to 3 tablespoons of unsweetened plant yogurt with live cultures per quart.
  7. Incubate 8 to 12 hours at about 110°F, covered and undisturbed. Extension guidance for dairy uses 110°F for 6 to 12 hours (University of Guam Extension).
  8. Chill at least 6 hours. Yogurt keeps firming as it cools in the refrigerator (University of Kentucky Extension), and starch or agar sets more as it cools.

Other causes

Prevention

  • Choose a plant milk with more protein; see our milk type vs texture matrix.
  • Add sugar and a thickener before heating, not after culturing.
  • Use a thermometer at the cooling step and in the incubator.
  • Use fresh starter, and confirm the batch cultured with the checks in how to verify your yogurt cultured.

When to throw a batch out

Texture alone is not a safety problem. These signs mean the batch goes in the trash:

  • Any mold. USDA says to discard moldy yogurt, because moist foods can be contaminated below the surface (USDA FSIS).
  • No tang at all after a full incubation. It never acidified, so it spent hours in the range where bacteria grow rapidly, 40°F to 140°F (USDA FSIS), with no acid to hold them back.
  • Rotten, yeasty or alcoholic smells, fizz, or pink or orange streaks.

Keep finished yogurt at 40°F or below. Illinois Extension advises eating homemade dairy yogurt within 14 days (University of Illinois Extension). No separate guideline exists for plant batches.

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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