Yogurt Manufacturing & References

Yogurt Types and Categories

The Yogurt Manufacturing Process

1. Mix preparation

Standardised milk base (typically 3.5–4.5% fat, 8.5–14% SNF depending on type). Higher SNF gives firmer body and reduces syneresis. SMP, condensed skim, MPC or UF retentate added for SNF boost. See dairy chemistry.

2. Heat treatment

Yogurt milk is heated higher than fresh milk pasteurisation — typically 85–95°C for 5–10 minutes. This denatures whey proteins which then bind to casein micelles, strengthening the gel and reducing syneresis. Skip this and yogurt is weak and watery.

3. Homogenisation

150–250 bar two-stage at the heat treatment temperature. Improves fat dispersion and contributes to gel structure.

4. Cooling to fermentation temperature

Cool to 42–43°C (thermophilic culture temperature).

5. Culture addition

Traditional yogurt uses the protocooperative pair: Streptococcus thermophilus + Lactobacillus delbrueckii subsp. bulgaricus. Modern products may add other cultures (Bifidobacterium, L. acidophilus) for probiotic claims.

6. Fermentation

For set yogurt: filled into retail pots, incubated in tunnel at 42°C until pH reaches 4.5–4.6 (~4–6 hours). For stirred yogurt: fermented in bulk tank at 42°C; stirred at end of fermentation.

7. Cooling and storage

Rapidly cool to <10°C to stop fermentation. Store at 2–4°C. Yogurt continues slow acidification over shelf life (3–4 weeks).

8. Optional: straining or stabilisation

Greek-style: centrifuge or UF to remove whey, concentrating protein from ~5% to ~10%. Drinking yogurt: stabilise with pectin to maintain pourable viscosity. Flavoured yogurt: add fruit, sugar, flavour after fermentation.

Yogurt Cultures

The classic pair

• Streptococcus thermophilus — faster initial acidification; produces flavour compounds; survives processing well
• Lactobacillus delbrueckii subsp. bulgaricus — deeper acidification; produces acetaldehyde (characteristic yogurt aroma); contributes to body

Additional cultures (probiotic positioning)

• Lactobacillus acidophilus — probiotic claim; gut health positioning
• Bifidobacterium bifidum / animalis / lactis — probiotic, often in "bio" yogurts
• L. rhamnosus, L. casei — specific strains with documented health benefits

Codex CXS 243-2003 defines "Yogurt" specifically as a fermented milk product containing the protocooperative S. thermophilus + L. bulgaricus. Products with only other cultures are technically "fermented milk", not "yogurt", under Codex.

Common Yogurt Product Variants

Common Quality Issues

Useful References & Standards

Frequently Asked Questions

What is the difference between set and stirred yogurt?

Set yogurt is fermented in the retail pot and never disturbed — the gel sets in situ giving a continuous, "shaky" structure when scooped. Stirred yogurt is fermented in a bulk tank, stirred to break the gel into small particulate "grains", cooled and packed — resulting in smoother, more pourable texture.

Why is yogurt milk heated higher than regular pasteurisation?

Yogurt milk is heated to 85–95°C for 5–10 minutes (vs 72°C/15s for fresh milk pasteurisation) to denature whey proteins. The denatured proteins then bind to casein micelles via disulphide bonds, strengthening the final gel and reducing syneresis. Skip this and yogurt is weak and watery.

Can yogurt be made without S. thermophilus and L. bulgaricus?

Under the international Codex standard (CXS 243-2003), "Yogurt" specifically requires the protocooperative pair Streptococcus thermophilus + Lactobacillus delbrueckii subsp. bulgaricus. Products made with only other cultures (e.g. just L. acidophilus) are technically "fermented milk" rather than "yogurt" under Codex.

What makes Greek yogurt different?

Greek (strained) yogurt has whey removed after fermentation by centrifugal separation or membrane filtration. The remaining product is ~2–3× more concentrated in protein (8–11% vs 4–5% in standard yogurt), with a thicker, creamier texture. The by-product (acid whey) is a major environmental challenge for Greek yogurt manufacturers.

Does yogurt cure lactose intolerance?

Not cure, but yogurt is generally well-tolerated by most lactose-intolerant individuals. The fermentation reduces lactose by 20–50% (depending on extent of fermentation), and the live cultures continue to break down lactose in the gut. Most clinical evidence supports yogurt as suitable for moderate lactose intolerance.

What's the shelf life of yogurt?

Chilled retail yogurt has 3–4 week shelf life from production at 4°C. Shelf life is limited by: (a) continued acidification during storage; (b) yeast and mould growth; (c) loss of culture viability (for "live and active" claims). UHT yogurt drinks can have 6 months ambient shelf life but lose culture viability.

What is Skyr?

Skyr is a traditional Icelandic strained dairy product, technically a fresh cheese but functionally similar to Greek yogurt. Made with specific cultures and a particular straining process, giving very high protein (~11%) and very low fat content. The category has grown rapidly outside Iceland with brands like Siggi's, Arla Skyr, and similar.

Further reading: John Watson publishes articles on dairy industry topics on LinkedIn. Browse all articles by John Watson on LinkedIn →

See related: Yogurt production consultancy, Yogurt structure, Frozen yogurt recipe development, Frozen yogurt process, Dairy chemistry, Milk pasteurisation, Homogenisation, Frozen yogurt consultancy, all dairy science information, consultancy services.