Acid Whey: Greek Yogurt's Two-Kilogram Byproduct Problem and What the Industry Does With It
Updated: 1 day ago
The arithmetic of strained yogurt is simple and unforgiving. Measured data from Greek dairies show that 100 kg of milk yields about 33 kg of strained yogurt and 67 kg of acid whey. Every tub of Greek yogurt therefore comes with twice its weight in a sour, cloudy liquid that has few buyers and cannot be poured away. When Greek yogurt went from under 1% to half of the American market in eight years, that liquid became an environmental story.
What acid whey is
Whey is the water phase of milk left after the proteins coagulate. Cheesemaking with rennet produces sweet whey (pH about 6), which the food industry has valued for decades as the source of whey protein powders and lactose. Straining yogurt, or making quark, cottage cheese or cream cheese, produces acid whey: coagulation happened through lactic acid rather than enzymes, so the whey is sour.
Typical composition of acid whey from Greek yogurt:
Property | Value |
pH | 4.2–4.6 |
Lactose | 3.3–5% |
Protein | 0.2–0.7% |
Lactic acid | 0.5–0.8% |
Calcium, phosphorus, potassium | present in meaningful amounts |
Biochemical oxygen demand (BOD) | about 46–50 g per litre |
Chemical oxygen demand (COD) | 52–64 g per litre |
The protein that makes sweet whey valuable has mostly stayed in the yogurt. What is left is lactose, acid and minerals in a lot of water.
Why it is a problem
Oxygen demand. A BOD near 50 g per litre is roughly a hundred times that of domestic sewage. Discharged into a river or lake, acid whey feeds bacteria that strip the water of dissolved oxygen and kill fish. Discharging it untreated is illegal in Greece, the EU and the US.
Hard to dry. Sweet whey is spray-dried into powders routinely. Acid whey's lactic acid and high mineral content make it hygroscopic and sticky; it clogs dryers and the powder cakes. Until recently that made the standard whey business model unavailable.
Volume. US Greek yogurt output reached about 771,000 tonnes in 2015, implying well over a million tonnes of acid whey a year from that country alone. Greece's 400,000 tonnes of yogurt in 2025, much of it strained, implies a comparable national stream.
Low value. Lactose and minerals in dilute solution are worth little; transport costs can exceed the value of the contents.
The 2013 story
In May 2013 Modern Farmer published "Whey Too Much: Greek Yogurt's Dark Side", estimating that producers in the US Northeast were generating more than 150 million US gallons of acid whey a year and asking where it went. Producers responded that most of it was being used responsibly: Chobani said more than 70% of its whey went to livestock feed and the rest to farmers for land application and digesters. The episode did not harm sales, but it made whey management a reputational issue and accelerated research into better uses.
Where acid whey goes today
Animal feed
The oldest and still the largest outlet. Dairy and beef cattle and pigs drink acid whey mixed into feed or water; its lactose is useful energy and the minerals are beneficial in moderation. Limits: it must be used fresh or kept cool, pigs tolerate more acid than cattle, and there are only so many farms within trucking distance of a plant.
Land application
Spread on fields, usually blended with manure, as a source of nitrogen, potassium and organic matter. Regulated by nutrient-management rules because over-application acidifies soil and risks runoff. Seasonal: you cannot spread on frozen or saturated ground.
Anaerobic digestion
Acid whey is an excellent feedstock for biogas digesters, where its lactose and acid are converted to methane for electricity or heat. Several large US plants, including Chobani's, send whey to on-site or partner digesters. The economics depend on energy prices and on having a digester nearby.
Protein and lactose recovery
Membrane filtration (ultrafiltration for protein, nanofiltration for lactose and minerals) recovers what little protein there is and concentrates the lactose for fermentation feedstock or for crystallisation. Returns are modest because the protein concentration is so low.
Deacidified powders
The technological breakthrough of the last decade. By removing lactic acid and some minerals with nanofiltration, electrodialysis or ion exchange, processors can produce an acid whey concentrate that spray-dries into a usable powder for bakery, confectionery and infant-formula ingredients. Arla, General Mills and others hold patents on variants of the process, and it turns the byproduct from a disposal cost into a saleable ingredient, at the price of capital-intensive equipment.
Food and beverage products
Smaller volumes go into whey-based drinks, sports beverages, fermented beverages, baked goods (acid whey works as the liquid in bread and pancakes, as home cooks know), and in Greece into traditional uses such as mizithra-type whey cheeses where the whey is sweet enough.
Reducing it at source
Ultrafiltering milk before fermentation concentrates the proteins so that less whey is produced afterwards, and what is produced is sweeter permeate rather than acid whey. Some manufacturers use this route; traditionalists note that it changes the protein profile of the finished yogurt. "Greek-style" products avoid the problem entirely by not straining, which is their main economic advantage.
Greece's situation
Greek yogurt production has doubled in ten years and most of the growth is strained product for export. Greek dairies are concentrated in Thessaly and Central Macedonia, regions with intensive agriculture and, in Thessaly, chronic water stress, which makes land application and effluent management politically sensitive. The large producers have invested in wastewater treatment and digesters as part of recent capacity expansions; the Mevgal and Kri Kri plant programmes of 2026–2030 include effluent and energy-recovery components. Smaller dairies still rely on local farms to take whey as feed.
The consumer's share
A home yogurt maker produces the same ratio: about half a litre of whey per litre of milk strained to Greek thickness. It should not go down the sink in quantity either; the kitchen uses are in How to make Greek yogurt at home. At industrial scale the question is the same, multiplied by hundreds of thousands of tonnes: a food that is prized for what has been taken out of it has to find a home for what was removed.
For the production process that creates the whey see How Greek yogurt is made; for the market volumes behind it see The Greek yogurt market in numbers.
Sources
Dairy (MDPI) 2025, 6, 21 — Greek strained yogurt: yields, acid whey composition (pH, lactose, protein, BOD/COD) and valorisation routes: mdpi-res.com (PDF)
Modern Farmer, "Whey Too Much: Greek Yogurt's Dark Side" (May 2013): modernfarmer.com
FoodNavigator, Greek yogurt firms respond on whey disposal (June 2013): foodnavigator.com
To Vima, Greek yogurt production and exports 2025: tovima.com
Newmoney, Mevgal second plant (2026): newmoney.gr; ESM Magazine, Kri Kri investment programme: esmmagazine.com
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