Cheese

How to reduce bitterness in aged cheese

An integrated approach to proteolysis control right across the cheesemaking process helps to reduce bitterness in aged cheese.

1. Introduction: bitterness is common but controllable

Cheese ageing is a delicate balance between flavor development and defect risk. While maturation unlocks complexity, it also introduces the possibility of off-flavors, particularly bitterness. Bitterness is one of the most common quality challenges in aged cheese, so it’s not surprising that the question: “How do I reduce bitterness in aged cheese?” is one we often hear from our customers. The answer lies in proteolysis — the enzymatic breakdown of proteins. With a clear understanding of why and how proteolysis happens, you can control it through the following approaches:

Optimization of protease activity
Enhancement of peptide degradation
Control of process parameters
Deployment of targeted adjunct¹ cultures
Control of storage parameters

2. The science behind proteolysis

2.1 Balancing peptide formation and degradation

Proteolysis is the central process governing cheese ripening. It involves the stepwise breakdown of casein proteins into progressively smaller components. The interaction between two enzyme classes drives this breakdown. Protease enzymes break down casein – the main protein found in milk - into peptides. Peptidase enzymes break peptides down into amino acids. When peptide formation exceeds peptide breakdown, bitter compounds accumulate in the cheese matrix. To reduce bitterness in aged cheese, you need to achieve the right balance between peptide formation and degradation.

2.2 What makes peptides in cheese bitter?

Not all peptides contribute equally to bitterness. Research shows that larger peptides, with 20+ amino acids, generally don’t contribute to bitterness. However smaller ones, with 4-12 amino acids, are usually key contributors to bitterness. These small peptides contain exposed hydrophobic side chains. These bind strongly to bitter taste receptors on the tongue. When caseins are broken down into smaller peptides, these normally “hidden” regions become exposed.

2.3 The three steps of proteolysis

Primary proteolysis This first step of proteolysis is driven by a range of proteases. Proteases present in milk include psychrotrophic bacteria. These cold-tolerant bacteria originate from environmental sources like soil, water, feed, and manure. They can grow at refrigeration temperatures. While they’re destroyed by pasteurization, they produce heat-stable proteases that can survive pasteurization. Proteases naturally present in milk include active plasmin and its inactive precursor plasminogen. Heat treatment during processing can impact plasmin activity. Primary proteolysis is also driven by starter culture proteases and coagulants. These are introduced during the cheesemaking process. Primary proteolysis breaks casein down first into large, then into smaller peptides. While the big peptides are not bitter, the smaller peptides are.
Secondary proteolysis Too much primary proteolysis without sufficient secondary breakdown is a common root cause of bitterness. So in this second step, which is driven by starter and adjunct cultures and Non‑Starter Lactic Acid Bacteria (NSLAB)², the goal is acceleration. By aiming for complete peptide breakdown in this step, you can reduce the bitter smaller peptides into amino acids.
Tertiary proteolysis Like secondary proteolysis, tertiary proteolysis is driven by starter and adjunct cultures and NSLAB. Its goal is the formation of amino acids and volatile compounds (aroma development). This step is crucial in driving cheese flavor in the desired direction.

3. The cause of bitterness in aged cheese

3.1 Why does cheese become bitter during storage?

Bitterness often develops or intensifies during storage because proteolysis continues after production ends. Even when bacteria are killed, the protease enzymes they produce can remain active and continue to hydrolyze proteins and peptides.

4. How to stop bitter peptides in cheese

Proteolysis is essential for flavor formation. But without careful management of peptide accumulation it can become the primary driver of bitterness. Proteolysis is shaped by the activity of cultures and enzymes. These play a central role in strategies to reduce bitterness in aged cheese. By managing the balance between peptide formation and degradation, you can stop bitter peptides in cheese and control bitterness in your aged cheeses. The following strategies will help.

4.1 Control Primary Proteolysis

By keeping activity low in this step, you reduce the number of small peptides, which in turn reduces bitterness. So control is the goal of primary proteolysis.

4.1.1 Good hygiene at farm level

Psychrotrophic bacteria are key drivers of primary proteolysis. They can get into milk through cows’ udders and through unhygienic milking or milk storage equipment. That makes good hygiene at farm level an essential control measure. Milk also needs to be stored for as short a time as possible, and at the correct temperatures. Proteolysis is accelerated by higher temperatures. So milk should be pasteurized as few times as possible and high heat treatment should be avoided.

4.1.2 Choose low-proteolysis coagulants

These are coagulant enzymes with a high ratio of clotting activity to proteolytic activity (C/P) ratio. Clotting activity measures how specific the enzyme is in targeting and cleaving kappa casein to form the curd. Proteolytic activity measures the enzyme’s non-specific breakdown of caseins into peptides. High proteolytic activity leads to higher peptide formation and the risk of bitter peptides accumulating. So the more specific the coagulant, the lower the proteolytic activity and the fewer unwanted peptides produced.

4.2 Control process parameters

4.2.1 Control pH during cheese make

The relationship between pH and syneresis kinetics during the cheese make has an impact on the retention of the coagulant enzyme chymosin in the curd and — ultimately — in the cheese. This in turn influences the proteolytic pathway. A lower pH at whey off increases the retention of chymosin in the curd. Therefore it’s essential to control the balance between pH development and syneresis, ensuring it matches the needs of the given cheese type. This helps avoid deviations in the process.

The balance between pH development and syneresis also affects the mineral content in the soluble phase. Changes in mineral equilibrium can influence flavor development, including bitterness. A higher level of ionized minerals in the soluble phase can increase the perception of bitterness in cheese.

4.2.2 Control salt/moisture and fat content

The salt in moisture content of the cheese, as well as the fat in dry matter level, can influence the perception of bitterness. A higher fat in dry matter level can reduce bitterness perception at a given level of small peptides. Similarly, higher salt and moisture levels can also help to decrease the perception of bitterness.

4.3 Accelerate Secondary Proteolysis

4.3.1 Use an adjunct/ripening culture

By selecting adjunct cultures with high peptidase activity you can accelerate the conversion of peptides, including bitter peptides, into amino acids, as well as improving flavor maturation and balance. Examples of adjunct cultures with high peptidase activity include Lc. lactis & cremoris and Lb. helveticus. These two cultures are widely used to enhance peptide degradation and reduce bitterness.

4.4 Control of storage parameters

Storage parameters strongly influence enzyme behavior and proteolysis balance. Ripening temperature is a critical variable to control bitterness. Lower temperatures support peptidase activity. Longer ripening time gives more time for the peptidases to break bitter peptides down into non-bitter amino acids. That shifts the balance away from peptide accumulation.

5. Key takeaways

Bitterness in aged cheese is not an unavoidable defect. It's a controllable outcome of how you manage proteolysis across your cheesemaking process. It arises when the protease-driven formation of small, bitter peptides outpaces their peptidase-driven degradation into amino acids. So the key to reducing bitterness in aged cheese is balancing protease and peptidase activity. You can achieve this by minimizing excessive primary proteolysis. Strategies include good on-farm hygiene, careful coagulant selection and optimal process conditions. Simultaneously, you need to accelerate secondary proteolysis. Strategies include using targeted adjunct cultures with strong peptidase activity, longer ripening times and lower ripening temperatures. These steps allow peptidases to complete peptide breakdown and enhance flavor development. This integrated approach will help you reduce bitterness in aged cheese and develop flavors people love.

By Sebastien Roustel, Head of Applied Research, Cheese Denmark, Novonesis
Sebastien is a senior expert in cheese science and dairy innovation, with extensive experience spanning research, application development, and industrial strategy. In leadership roles including Associated Director of Cheese Applications, and Senior Principal Scientist, he has guided scientific and technological direction and managed large, cross‑functional teams. With deep expertise across all cheese types, Sebastien combines strong technical knowledge with practical industry insight, covering product characterization, culture and enzyme applications, and milk optimizations. His career also involves lecturing, publications, and directing R&D at École Nationale de l'Industrie Laitière et Biotechnologies (ENILEA of Poligny/Mamirolle) and serving on the editorial board of Techniques de l’Ingénieur and Profession Fromager journals, with more than 100 publications.