Acid whey in sourdough: Fixing a commercial pain point or provoking the purists?

Key takeaways:

• Replacing 50% of water with acid whey increased loaf volume, delayed mould growth and outperformed commercial sourdough in consumer preference tests.
• While functionally effective, acid whey raises definitional and labelling questions when used alongside baker’s yeast in products marketed as sourdough.
• With Greek yoghurt production generating large volumes of acid whey, bakery could offer a commercially viable route for upcycling a growing dairy byproduct.

Sourdough has always traded on simplicity: flour, water, salt, time and a living starter. For artisan bakers, that’s not just a method but a philosophy. So the idea of introducing a dairy byproduct into that equation is bound to raise eyebrows.

Yet new research published in the Journal of Food Process Engineering suggests that acid whey – the nutrient-rich liquid strained off during Greek yoghurt production – could address some of sourdough’s most persistent commercial pressures. Higher loaf volume. Slower mould growth. Stronger consumer preference. And a sustainability story retailers would readily support.

The balancing act is familiar for commercial bakers. Authenticity carries weight, but so do throughput, shelf life and ingredient lists that don’t stretch uncomfortably long. Clean label reformulation is now standard operating reality. Acid whey lands squarely in that conversation.

Latifeh Ahmadi, professor in the Brescia School of Food and Nutritional Sciences, set out to test whether this dairy byproduct could function as a fermentation aid in breadmaking. “It’s the same type of culture that’s used in bread baking. Instead of combining water with yeast, we’re replacing half of the water with our acid whey,” she said.

Bigger loaves, longer life, stronger preference

Acid whey is generated in substantial volumes. In Greek yoghurt production, roughly 67% of the milk input becomes acid whey, leaving just 33% as finished yoghurt. That matters in a market that reached around $9bn in 2025 in the US alone – accounting for more than half of the American yoghurt category – and which Statista forecasts will exceed $13bn globally by 2028.

It’s not an inert byproduct. Acid whey contains lactose, minerals and soluble proteins, giving it high biochemical and chemical oxygen demand. Disposed of untreated, it can deplete oxygen in waterways.

“The problem with all this acid whey is that it can’t be dumped – it would destroy the surrounding environment,” Prof Ahmadi warned. “Because it’s full of nutrients, it would feed a lot of hungry microorganisms in the environment, sparking rapid growth that consumes oxygen and pollutes waterways.”

Rather than treat it purely as waste, her team treated it as an ingredient.

In controlled trials, 50% of the water in a standard white bread formulation was replaced with liquid acid whey. The resulting acid whey bread (AWB) was compared with standard white bread (WB) and a commercial sourdough bread (CSB).

Loaf volume in the acid whey bread reached 1,550cm³ – significantly higher than white bread at 1,375cm³ and also above the commercial sourdough at 1,450cm³.

pH dropped from 6.07 in white bread to 5.17 in acid whey bread, moving it closer to sourdough territory (4.73). Under identical storage conditions, mould developed more slowly in the acid whey bread than in the standard white loaf.

“Because the acidity in our bread is higher, mould won’t show up as quickly, giving us the chance for a cleaner label,” Prof Ahmadi said.

Aeration levels were comparable to the commercial sourdough. Moisture content showed no significant differences. Firmness and staling behaviour followed similar patterns.

Consumer testing may be the most persuasive element. In a blind sensory evaluation involving 81 participants, acid whey bread scored significantly higher than commercial sourdough for flavour, aroma, softness and overall acceptability. When asked which loaf they would purchase, 62 out of 81 participants (76.5%) chose the acid whey bread.

“The result was incredible: the physical properties of the bread were compatible, and in our sensory evaluation most participants preferred our bread over the commercial one,” Prof Ahmadi said.

Not entirely new but commercially sharper

Whey in bread isn’t new. Previous research has explored whey powders and fermented dairy ingredients in pan breads and sourdough-style systems, often reporting improvements in softness and flavour development.

What distinguishes this study is its use of liquid acid whey from Greek yoghurt production, its direct comparison with a commercial sourdough product and its inclusion of purchase-preference data. It brings sustainability, functionality and consumer response together in one controlled evaluation.

Why it works

From a fermentation standpoint, acid whey contains lactic acid bacteria (LAB) – the same broad microbial group central to sourdough fermentation. In the study, acid whey contained 2.75 × 10⁷ colony-forming units per millilitre.

These bacteria help acidify the dough and influence gluten behaviour, supporting gas retention and crumb softness. Commercial instant yeast was still used in the formulation to ensure consistent carbon dioxide production and predictable rise.

Fermentation remains central. Acid whey supports it rather than replaces it.

But whether that qualifies as sourdough is where debate begins. “My initial thoughts are that we wouldn’t have an issue with bakers using whey from natural yoghurt production in bread making,” opined Chris Young, coordinator of the Real Bread Campaign. However, he noted that “issues for us could include whey that was a byproduct of coagulation caused by the addition of industrially produced acids and / or if acidified whey was being used in combination with baker’s yeast and /or additives in products marketed using the word sourdough.”

In Prof Ahmadi’s study, commercial instant yeast was used alongside acid whey. The dough was acidified through naturally occurring lactic acid bacteria, but it wasn’t built solely on a flour-and-water starter. That distinction may prove decisive for those who argue that sourdough is defined by process rather than flavour profile.

So the debate shifts from whether acid whey functions – it clearly does – to how such products are described. Is this sourdough in the strictest sense? Sourdough-style? Or something else entirely?

For bakeries that trade heavily on heritage and purity, that distinction matters. Acid whey introduces a milk allergen, removes vegan eligibility and alters the simplicity narrative that underpins many sourdough claims.

Commercial producers face a different set of pressures. Throughput, consistency and shelf life are constant considerations. Long fermentation cycles tie up capacity. Clean label reformulation remains relentless. Viewed through that lens, acid whey looks less like dilution and more like fermentation engineering.

From waste stream to workable ingredient

As Greek yoghurt production continues to expand, scrutiny around acid whey disposal will only intensify. While some volumes are diverted into feed or other applications, significant quantities remain underutilised.

Bakery could offer a higher-value destination. But there are practical considerations. Liquid acid whey is perishable and bulky. Standardisation would be critical for large-scale adoption. Freeze-drying is technically feasible, according to Prof Ahmadi’s team, but adds cost.

“My dream is that one day this sustainable solution will be used throughout industry,” she said. “When it comes to food waste, we often talk about the use of energy, land, water and fertilizer – but we should consider the food industry just the same. Coming at the problem from new angles like this is key for our future.”

Acid whey is unlikely to displace traditional flour-and-water sourdough in bakeries that define themselves by restraint. For some, the moment an external dairy byproduct enters the mix, the product ceases to be sourdough in its purest sense.

But sourdough is no longer confined to craft counters. It is a multibillion-pound retail category. It sits on supermarket shelves as much as it does on wooden bakery boards. And categories, once commercialised, rarely remain untouched.

The data suggest acid whey delivers measurable advantages: higher volume, delayed mould growth and strong consumer preference. From a formulation standpoint, that’s difficult to ignore.

So the tension may not be about whether acid whey works. It plainly does. It’s about whether the industry wants sourdough to remain a method defined by discipline or a format defined by performance. And if the latter prevails, the debate over what qualifies for the name is only just beginning.

Study:

Basmah Al-Janabi, Sharareh Hekmat, Latifeh Ahmadi. Valorization of Acid Whey to Product Sourdough Bread Starter. Food Process Engineering, Vol 49, Issue 1, January 2026. https://doi.org/10.1111/jfpe.70321