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A starter culture does more than lower pH. This review sets out how lactic acid bacteria turn milk sugars, proteins and fats into acid, texture and flavour, and how the underlying genetics affect those functions. For cheesemakers, its value is in explaining why cultures with similar species lists can behave differently in the vat and during ripening.

The question and the scope

Thomas Bintsis brings together research on the metabolism and genetics of the main groups of lactic acid bacteria used in fermented foods. This is a 2018 review, not a new cheese trial. The useful question is how a culture’s metabolic pathways and genetic traits translate into acidification, flavour development, texture and consistency. The discussion extends beyond dairy; the points below concentrate on cheese.

1. Acidification is the first job, but not the only one

Homolactic fermentation directs most of the sugar carbon towards lactic acid. Heterolactic fermentation also produces carbon dioxide and ethanol or acetate. That distinction matters when selecting for a close texture, gas formation or a particular flavour profile. The pathway used depends on the organism, the substrate and the conditions; a culture’s behaviour cannot be reduced to a single species label.

Pyruvate sits at a major branch point. Carbon passing through it can end up as lactate or be diverted towards compounds including diacetyl, acetoin, acetaldehyde and acetate. The balance changes with the strain and its environment. An acceptable final pH therefore tells us relatively little on its own about the aroma the culture will produce.

2. Citrate metabolism links buttery flavour and gas

Citrate-positive lactococci and Leuconostoc can use citrate and contribute diacetyl and related aroma compounds, as well as carbon dioxide. Citrate transport is a critical part of that ability; in citrate-positive Lactococcus lactis, it is associated with a plasmid. The review also describes the influence of pH and the availability of sugars on the products formed.

For cheesemakers, this helps explain why an aromatic culture can affect both flavour and openness. A culture selected for buttery notes may also bring gas production. The result still depends on its partners and the make conditions; adding a citrate user does not guarantee a fixed diacetyl level or a particular eye pattern.

3. Protein breakdown is central to ripening

Milk contains relatively little free amino acid. Many LAB cannot make all the amino acids they need, so their ability to break down casein and use peptides is important to growth as well as ripening. Proteinases and peptidases produce progressively smaller peptides and amino acids, which then provide substrates for further flavour reactions.

The practical distinction is between producing acid promptly and developing the desired flavour over time. A useful adjunct may contribute to the latter without being the main vat acidifier. Non-starter LAB, including organisms described in the paper as L. paracasei, L. plantarum, L. rhamnosus and L. casei, can become important during maturation. Their contribution is strain dependent; their presence alone does not establish a beneficial result.

4. LAB have a limited direct role in fat breakdown

The review describes LAB lipolysis as limited, while noting esterase activities and the importance of fatty acids as flavour compounds and precursors. Fat breakdown can supply compounds that contribute directly to flavour or feed subsequent reactions producing esters and other volatiles. A claim that a starter “develops flavour” should therefore be read more specifically: which pathway, which strain and under what ripening conditions?

5. Important dairy traits can sit on plasmids

In lactococci, plasmids can carry functions involved in lactose use, casein breakdown, bacteriophage resistance, bacteriocin production and exopolysaccharide production. Plasmids are DNA elements separate from the main chromosome. Their exchange and rearrangement can support adaptation, but can also contribute to instability in useful functions.

This is one reason strain identity and culture maintenance matter. Two cultures carrying the same species name need not have the same acidification performance, proteolytic activity or phage resistance. The review gives bacteriophage resistance and metabolic stability as explicit selection criteria for lactococcal starters. A species list is a starting point, not a complete performance specification.

6. The main culture groups do different work

Group	Relevance to cheese
Lactococci	Mesophilic acidification and flavour development; several important dairy functions may be plasmid encoded.
Streptococcus thermophilus	A dairy-adapted thermophilic starter. The review discusses sugar and protein metabolism, acetaldehyde and polysaccharide production. Its plasmids generally play a smaller functional role than those of lactococci.
Lactobacilli	A diverse group containing starter and non-starter organisms. The paper covers thermophilic dairy species such as L. helveticus and L. delbrueckii, as well as organisms associated with maturation. Do not treat all lactobacilli as thermophilic.
Pediococci	P. pentosaceus can form part of the non-starter flora of ripening cheese. Sugar use and bacteriocin production can be linked to plasmids.
Leuconostocs	Heterolactic metabolism and citrate use can contribute carbon dioxide, diacetyl and acetoin.

7. Texture and protective functions need separate consideration

Some LAB produce exopolysaccharides, which can affect the physical properties of fermented products. Others produce bacteriocins or other inhibitory metabolites. These are distinct culture functions, not automatic properties of every strain within a species. The review’s discussion of enterococci also makes clear that occurrence in a traditional fermentation is not sufficient grounds for starter selection.

8. Genetics explains possibilities, not a ready-made make schedule

The review describes metabolic engineering that redirects pyruvate away from lactate and towards compounds such as diacetyl. These examples show how changing a particular genetic function can alter the fermentation output. They do not show that ordinary commercial cultures have been engineered in this way, or supply a dosing instruction for a home make.

Genome information helps identify potential functions, but actual performance still needs testing in milk and cheese. For my purposes, I would compare cultures against four separate requirements: the acidification curve through the make, the intended flavour contribution, the effect on texture and gas, and reliability across repeated batches. A promising genetic trait is useful evidence; it is not a substitute for those measurements.

Limits and reading notes

This is a broad review of the literature available in 2018. It does not provide a controlled comparison of current retail starter blends, universal pH targets or culture dose conversions. Organism names are retained as printed in the paper; several names and classifications have changed since publication. Its strongest use is as a framework for asking better questions about a culture, rather than as a catalogue of guaranteed effects.

Source and free full text

Bintsis, T. (2018). Lactic acid bacteria as starter cultures: An update in their metabolism and genetics. AIMS Microbiology, 4(4), 665–684. DOI and publisher record.

Open access — free to read. Read the complete article on PubMed Central. The article is distributed under CC BY 4.0. No payment or ResearchGate account is needed for this copy.

What matters more to a Raclette’s melt: how low the pH goes, when it falls, or how much calcium remains bound in the curd? Fröhlich-Wyder and colleagues tested milk pre-ripening and citric or lactic acid additions in model Raclette cheeses. For cheesemakers, the interest lies in connecting the make, calcium retention and pH history with what the cheese actually does under heat.

Main findings

The stronger citric-acid treatment reduced both total and insoluble calcium. After 14 weeks, total calcium was 3,846 mg/kg against 4,809 mg/kg in the control; insoluble calcium represented 11.1% against 23.4%. Pre-ripening lowered the milk’s starting pH but increased total calcium in the finished cheese relative to the control. Earlier acidification therefore did not automatically mean greater calcium loss.

Citric and lactic acid were not interchangeable even when they produced the same whey pH: citrate also binds calcium. The citrate cheeses behaved more firmly in instrumental heating tests, yet the sensory panel still assessed their melting qualities favourably. Many sensory differences were not statistically significant. The practical lesson is to assess actual serving performance alongside pH and laboratory measures of melt.

Core model recipe and ingredients

The experimental batch used 50 litres of milk standardised to 33 g/kg fat (3.3%), pasteurised at 70°C, with 10 ml of 35% calcium chloride. RSW 901 starter from ALP was added after cooling to 28°C, followed by 45 minutes of ripening at 28–32°C. The make then used 8 ml Hansen Standard 225 rennet extract and 1 litre water, with coagulation at 32°C for 35 minutes. The paper does not specify starter dose, pasteurisation holding time or a directly usable rennet potency.

The curd was cut to 15–25 mm, stirred for 15 minutes, then raised to 35°C over 10 minutes while adding 22 litres of water. A further 25 minutes of stirring at 35°C preceded pressing. The pressing room was held at 30°C for the first 45 minutes; cheeses were turned repeatedly. Brining lasted one day at 11–13°C, followed by smear ripening for 14 weeks at 10–11°C and 90–96% relative humidity. These are pilot-plant methods, with some details absent, rather than a complete home recipe.

Alongside the control, one treatment pre-ripened milk with 5‰ Lactococcus lactis 17 culture at 16°C for 15 hours before pasteurisation. The other treatments added either 25 or 50 g citric acid monohydrate, or 35 or 70 g of 90% lactic acid, per 50-litre batch during washing. Acid contact before pressing was at most about 35 minutes. These were alternative experimental treatments, not ingredients to combine in one make.

The control cheese’s acidification curve through the make

The useful reference for a cheesemaker is the rate and timing of acidification, especially the unacidified control (CON). Figure 2 on printed page 470 follows coagulation and fabrication, then 0, 1, 2, 3, 4 and 24 hours, and finally 14 weeks. The authors identify 0 h as the start of pressing. The hourly clock therefore begins after the vat make, not at culture addition or renneting.

Make stage / elapsed time	Control pH	How to read it
Coagulation	≈6.5	Vat milk at coagulation
Fabrication	≈6.5	Curd treatment before pressing; source stage label
0 h	≈6.5	Start of pressing; not the time of starter addition
1 h	≈6.1	First hour after pressing begins
2 h	≈5.7	Second hour after pressing begins
3 h	≈5.4	Third hour after pressing begins
4 h	≈5.2	Approaching the brining checkpoint
24 h	5.08	Exact mean from Table II
14 weeks	5.35	Exact mean from Table IV; later ripening, outside the make

Approximate graph readings: values marked ≈ are read from Figure 2 and rounded to about 0.1 pH unit; the underlying hourly data are not tabulated. They are mean results from two batches, not a prescribed make curve. Coagulation and fabrication are categorical stages on the original graph, so their horizontal spacing does not establish elapsed time.

The control stays near pH 6.5 during coagulation and fabrication, then acidifies rapidly under the press: about 6.1 at one hour, 5.7 at two hours, 5.4 at three hours and 5.2 at four hours. It reaches the lowest 24-hour pH of the treatments, 5.08, before rising to 5.35 during ripening. The manufacturing protocol calls for brining at pH 5.2 after roughly 4–6 hours. These details make the control a useful comparison for a make log: follow how quickly the curd moves through the first hours under pressure, as well as its pH on entering the brine.

The contrasting acid-added treatments lose pH earlier, when wash water is added, and follow flatter subsequent curves. The control’s stronger fermentation during the first day allows calcium to continue leaving under the press and in the brine. This is why pH at drainage, terminal pH and a wash-whey reading each describe different parts of the process.

Source for the curve: Fröhlich-Wyder et al. (2009), Figure 2, p. 470; time-zero definition in section 3.1.3, p. 471; brining protocol in Figure 1, p. 467. Original paper and acidification graph.

Source

Fröhlich-Wyder, M.-T., Guggisberg, D. and Wechsler, D. (2009). Influence of low calcium and low pH on melting characteristics of model Raclette cheese. Dairy Science & Technology, 89, 463–483. Read the original paper: doi:10.1051/dst/2009025. This overview summarises the supplied paper; its PDF is not reproduced here.

Main question: How does the diet of milk-producing cows, sheep and goats alter the volatile compounds that develop in cheese, and through which biochemical pathways? This 2020 review brings together evidence on pasture, conserved forage, plant by-products and trace-element supplementation.

Diet can influence aroma by changing milk composition and the substrates available during ripening, as well as microbial and enzyme activity. The review follows the breakdown of fat and protein, alongside lactose, lactate and citrate metabolism, into acids, aldehydes, lactones, ketones, alcohols and esters. Some plant-derived compounds may also reach milk more directly.

The reported effects are specific to the feeding treatment and cheese. Grape pomace and liquorice supplementation reduced selected short-chain fatty acids in some trials, while zinc supplementation increased butanoic and hexanoic acids in certain dairy products. Zinc and selenium were associated with increased concentrations of particular lactones in Caciotta; zinc also increased several lactones and ethyl esters in ripened Caciocavallo. Proposed explanations involving bacterial autolysis and lipase activity remain hypotheses.

Pasture composition can change the volatile profile. Ragusano made from milk of cows receiving native pasture alongside a total mixed ration contained eight aroma-active compounds absent from the comparison cheese. In a Montasio study, different alpine pastures altered ketones, phenolic compounds and terpenes, but the sensory differences detected by the tasting panel were slight.

Cheesemaking can modify or remove dietary effects. In one olive-pomace trial, differences in free fatty acids, esters and ketones measured in raw milk disappeared after pasteurisation and cheesemaking. Starter cultures and ripening conditions therefore matter alongside the feed itself.

The central finding is that feeding strategy can alter cheese aroma chemistry, but the evidence does not establish a universal route from a particular feed to a predictable flavour. Compound concentrations alone do not demonstrate improved taste or consumer preference. The authors call for better understanding of direct feed-to-milk transfer, interactions with the cheese matrix and the combined sensory effects of volatile compounds.

Source: Ianni, A.; Bennato, F.; Martino, C.; Grotta, L.; Martino, G. (2020). Molecules, 25(3), 461. DOI: 10.3390/molecules25030461. Published 22 January 2020.

The attached article is reproduced unchanged under the Creative Commons Attribution 4.0 licence (CC BY 4.0). The text above is a summary of the review. Original article: https://doi.org/10.3390/molecules25030461. Licence: https://creativecommons.org/licenses/by/4.0/.

Link to original article: https://cdr.wisc.edu/controlling-acidity-moisture

CENTER FOR DAIRY RESEARCH

Measuring and Controlling Acidity and Moisture During the Cheesemaking Process

Why Measure Acidity and Moisture?
“All cheesemakers should be monitoring acidity and moisture because they drive how the cheese is going to turn out,” explains Andy Johnson, former outreach specialist/assistant coordinator, CDR Cheese Industry and Applications group.

Dean Sommer, CDR cheese and food technologist, agrees, “Controlling acidity and moisture content those are two of the really big keys to successful cheesemaking. A lot of cheese defects are from improper moisture content and improper rate and extent of acid development”.

Cheesemaking is ultimately a concentration process that involves monitoring and controlling multiple factors and reactions. “We’re reducing the moisture content, we’re concentrating fat, we’re concentrating protein and we’re using up a large majority of the lactose retained in the curd to develop a significant amount of lactic acid, which drops the pH,” Sommer said.

Milk has a pH of about 6.7, but during cheesemaking acid is developed and the pH drops, i.e., Cheddar has a pH of about 5.2. The cheesemaking process also reduces the moisture content—milk typically has a moisture content of about 87% whereas Cheddar has a moisture content of about 37%.

However, cheesemaking isn’t just about reaching a final moisture level or pH; it’s about controlling the loss of moisture and the rate and extent of acid development. As cheesemakers say, “The journey matters”. Therefore, it’s important to measure and control acid development and the process of moisture reduction during cheese manufacture. Acid and moisture impact the flavor, microbiological content, and structure/texture/body of the cheese.

Why Keep Records?
A good cheesemaker is also a good record keeper. This is especially true when it comes to measuring and recording acidity during cheesemaking.

“If you have a defect or run into a problem with your cheese, it’s almost impossible to figure out what happened if you don’t have a record of the pH development,” Johnson said.

Cheesemakers need to be able to back and look at their records to see the “journey” that their cheese took during the cheesemaking process. Johnson recommends that cheesemakers detail all observations (not just pH), especially if something is abnormal like odor or the color. Record the milk quality measurements, heat treatment (time/temperature) and starter growth conditions. Keep detailed records during manufacture of the pH, temperature, time, and curd firmness. Ideally, all batches of cheese would be tested for composition and microbiological quality.

Issues with Improper Acid Development
Again, a lot of common defects seen in cheese are related to an improper rate and extent of acid development (too little, too much, too fast, too slow). Here are some of the characteristics associated with excessive or inadequate acidity:

Excessive acidity (low pH) characteristics of cheese:
Short/brittle body in dry hard cheese. Pasty body in soft cheeses. Grainy texture and acid (bitter) flavor. Cheese loses serum, which results in sweating. The cheese is more prone to developing calcium lactate crystals and microorganisms at the surface of the cheese (rind rot if packaged). A common underlying cause of these issues is excessive starter activity.

Inadequate acidity (high pH) characteristics of cheese:
There is a food safety concern (pH > 5.6). The curds may not knit very well. A short, crumbly cheese body and a tough, corky texture. Can result in poor functionality/melt/stretch. Underlying cause excessive calcium remaining bound to the casein (more on this later).

Measuring and Recording Acidity
What is pH exactly? It is a measurement of the concentration of hydrogen ions. A neutral pH is 7.0 (e.g., water). A low pH, like 2.0, is very acidic (e.g., orange juice). A high pH, like 12.0, is very basic (e.g., caustic soda). As mentioned, milk typically has a pH of 6.7.

One important aspect of the pH scale is that it is logarithmic. For example, a pH of 5.0 is 10 times more acidic than 6.0. “What this means to a cheesemaker is that if you’re shooting for a 5.2 pH and you get a 4.9—that’s a big deal,” Johnson said. “And if you’re shooting for a 6.2 and get a 5.9 or 5.8—that’s a huge deal. You’ve basically made a different cheese”. Tenths of a pH unit make a difference in cheesemaking.

Most cheesemakers measure pH by using a pH meter (Potentiometric Method). A pH meter is composed of a pH electrode (probe) connected to a voltmeter (pH meter).

How does a pH meter work?
Two electrodes (housed in one probe) form a circuit and measure the voltage output of the hydrogen ions. Then the pH meter translates the voltage output into a pH.

The pros of pH meters are that they are highly accurate if calibrated correctly and easy to operate. They also compensate for temperature, which can impact pH accuracy. The cons of a pH meter are that pH probes do require regular cleaning and calibration; otherwise readings will be inaccurate. Also, good meters and probes are expensive, and any needed repairs or replacement parts will also be costly (probes are typically a few hundred dollars). There are less expensive models that cheesemakers can successfully use but these are not ideal to work with and will need to be replaced every year or so. When purchasing a pH meter, you also need to keep in mind that separate probes are needed for milk or whey and cheese.

Make sure to follow the manufacturer’s instructions for probe care and maintenance (proper storage will extend the life of your probe and maximize its performance). A big tip is to never store the probe in distilled or deionized water—this will cause ions to leach out of the glass bulb of the electrode and will eventually ruin it. CDR recommends that the probe be stored in a solution of 3M KCL (never store the probe dry).

Taking a pH Reading
The process of taking the pH of milk/whey or curd is relatively simple although it is important to do it correctly. To take a pH reading of a liquid sample (milk or whey), first take the probe out of the storage solution and rinse it with distilled water, blot it dry (with a laboratory wipe like Kimwipes or similar), immerse the probe in the milk or whey and gently stir the milk/whey with the probe and keep agitating it with the probe until the meter reaches a stable reading. Then take the probe out of the milk, rinse the probe and return it to the storage solution.

Taking a pH reading of a curd sample is similar. First you take the probe (a spear tip probe for solids) out of the storage solution, rinse it and blot it dry. Then get your curd sample and squeeze it to get as much whey out of it as possible. Insert the probe into the cheese and hold the probe in the cheese until the reading stabilizes. Once you have a reading, remove the probe, rinse it, blot it dry and return it to the storage solution. For more details on taking accurate pH readings, you can refer to the book Standard Methods for the Examination of Dairy Products (Wehr and Frank, 2004).

One issue cheesemakers face is the question of whether to record pH for both whey and curd. Some cheesemakers measure the pH of the whey, some do the curd, and some, like CDR, record both.

“You probably do not need to measure both whey and curd, but one thing to keep in mind is that you need to be consistent in which you measure because they are different,” Johnson said. “Typically, the curd pH is 0.1 to 0.2 units lower than the whey”. If a cheesemaker adds water or rinses the curd, a pH measurement of the curd is desired. The curd is usually lower in pH because the curd is where the starter bacteria are creating the acid and releasing it into the whey. One advantage of measuring both curd and whey is that you can get a good indication of how fast your acidification is going based on how far apart the pH is of the whey and curd.

Titratable Acidity
Before pH meters, cheesemakers used a titrator or acidometer to measure titratable acidity (TA) of milk or whey. Titratable acidity is related to pH in that the more acid developed, the higher the TA. TA is also a measurement of the buffer capacity of the milk or whey. Of interest to cheesemakers is the calcium phosphates, which have a direct effect on the buffering capacity of the milk. The more casein in milk, the more calcium phosphate. Since the calcium phosphate is the main buffer in milk and TA measures buffer capacity, a higher TA sometimes is not associated with more acid; it is the change in TA over time (more starter culture activity) that the cheesemaker needs to monitor.

Additionally, if you have a seasonal milk source, casein and calcium phosphate will change throughout the season so TA is a good way to monitor these changes in the milk. The actual process of taking a TA reading is more complicated than taking a pH reading.

As a cheesemaker, if you have to pick one (pH or TA) it is recommended that you use pH because pH will give a consistent reading between cheesemakers and a pH meter is able to measure the pH of liquids (milk/whey) and solids (curd). Some cheesemakers who use high solids milk will use both because TA will indicate starter activity sooner than pH. Milks high in calcium phosphate may show little change in pH but a large change in TA.

Role of Acidification in Cheesemaking
Acid development drives the cheesemaking process. Acid development occurs because the starter bacteria ferment the lactose in the milk and produce lactic acid, which drives the necessary reactions for cheesemaking. One of those reactions is that the lactic acid solubilizes colloidal calcium phosphate and thus helps determine the level of calcium in the cheese curd and the ratio of soluble to colloidal calcium. These factors, in turn, greatly influence cheese texture and functionality. Acidity also impacts the activity of the coagulants during manufacture and ripening. Acidity promotes syneresis (expulsion of moisture from the cheese curd) and therefore has a large impact on cheese composition, particularly the moisture content of the cheese. The lactic acid also influences the activity of enzymes during ripening and, hence, affects cheese flavor and quality. Finally, acidity helps control or prevent the growth of spoilage and pathogenic microorganisms.

Acid takes time to develop during the cheesemaking process; the starter cultures need time to ferment or consume the lactose. So, at the beginning the pH is higher but it drops during cheesemaking. As mentioned, lactose is the fuel for acid development; the more lactose, the more lactic acid that can be produced. Fortifying the cheese milk with extra lactose containing solids (condensed skim, NDM) will add more lactose to the system, allowing for more lactic acid to be produced resulting in a lower pH cheese. Conversely, cheesemakers can remove some lactose from the milk by using ultrafiltration (UF) and adding back water into the UF milk. This will help remove some lactose from the system, resulting in less of a pH drop in the cheese. CDR has been promoting this method as a strategy to avoid making “acid cheese”.

“One of the single biggest cheese defects we’re seeing is acid cheese,” Sommer said. “We’re doing a lot of work using ultrafiltered cheese milk and diluting it with water. This brings down the ratio of lactose to protein. So, there’s less lactose in the system and you don’t develop acidy cheese”.

ACID PRODUCTION
Lactose + Energy (Starter cultures) = Lactic Acid

Acid Development During Cheesemaking
Now, let’s get into acid development during the cheesemaking process. Again, it is critical to measure and record the acidity during the cheesemaking process (including during aging and of the final cheese). This is where a good make sheet with a lot of data points is crucial. For example, at a minimum, cheesemakers should be recording pH of the initial milk, before adding the coagulant, at cut, during milling/salting and hoaping/tinning. We also need to continue recording the pH during ripening/aging at day 1 and so on.

It’s important to measure the pH of the initial milk because you want to know the “starting point” of the cheese. The pH of the initial milk will give an indication of the quality of the milk, for instance, if the pH reading of the milk is high (more than 6.8) this is likely a sign of mastitis; if this is the case, you will want to monitor the somatic cell count of the milk. Recording the pH of the initial milk is helpful in other ways as well. For instance pasteurization slightly lowers the pH, also the stage of lactation will impact pH and the type of milk (seasonal milk, sheep or goat milk) will also impact pH. In general, if the pH of the initial milk is off you will want to investigate why.

Creating Wet Acid
The next point in the cheesemaking process when it’s important to know and record pH is before adding the coagulant. This is when the cheesemaker is creating “wet acid”. It’s called “wet acid” because you are creating acid before draining the whey. Monitoring acid at this point is important because wet acid development has the greatest impact on calcium solubilization. A lower pH before coagulant addition will allow more calcium to be solubilized (removed) from the casein (this also results in a higher moisture cheese).

For example, we can have two cheeses that both have a final pH of 5.2. Even though they have the same final pH, one has a curdy texture and the other has a nicer, less curdy body that allows for an easier shred. The difference is that the curdy cheese had a pH of 6.5 at coagulant addition compared to the nicer cheese, which had a pH of 6.35 at coagulant addition.

“That’s the power of creating wet acid where you’re solubilizing calcium,” Johnson says. This also illustrates how a “small” variation in pH (6.5 compared to 6.35) can have a big impact on the final cheese.

This also brings up an important point regarding the development of “wet” versus “dry” acid. As mentioned, wet acid is developed early in the cheesemaking process and up to the point that the whey is drained. Dry acid is developed after the whey has been drained and the cheeses moved to hoops or forms (the acid is developed when the cheese is “dry”). The wet and dry acid dynamic is an important concept for cheesemakers to understand.

For instance, let’s say we’re making Cheddar. Sommer says he wants the pH to be 5.4 when the Cheddar is going into the hoop because a lower pH reading at this point shows that he has created wet acid (the pH has lowered) before the whey was drained. However, Sommer said that a lot of cheesemakers rely on dry acid and will hoop their Cheddar when it has a pH between 6.0-6.1.

“I’d run screaming out of the door if I saw that,” Sommer said. Why? Because, if a cheesemaker develops acid in the milk or curd/whey (wet acid) then a lot of the lactic acid will go in the whey and will be removed when the whey is drained. Conversely, if acid is developed in the hoop (dry acid) where will that lactic acid go? It will stay in the cheese. This results in an acid Cheddar that is more likely to develop a bitter taste, whey taint flavors and defects like calcium lactate crystals.

Cheesemakers next need to record pH when draining the vat. As described previously, this pH reading will let the cheesemaker see if they have developed the right amount of acid, depending on whether they were trying to develop wet acid or if they are relying on more dry acid development. When draining the vat, we are taking lactose away from the bacteria, which will slow down acid development.

If making a milled or stirred curd cheese, you will want to measure pH before milling and before salt addition, respectively. Knowing acid development before adding salt will allow you to better target final pHs in your cheese as some cultures are inhibited by salt.

For a brined cheese, whether you’re pumping the curd into a pre-press or taking it right out of the vat to hoops, you want to measure an acidification point at hooping because at this step you’re basically switching from forming wet to dry acid formation. It’s important to get this acid reading for eyed cheeses as typically you want a lot of unsolubilized calcium in the curd with these styles of cheese.

Buffering—Loss of Insoluble Calcium
Tracking and recording pH doesn’t stop when the cheese is out of the vat. It’s very important to record the history during post manufacture because you want to find the lowest terminal pH that the cheese reaches.

“That (lowest terminal pH) is going to determine a lot of the final characteristics of your cheese,” Johnson said. It’s also important to record the cheese pH after manufacture because this is when the cheese pH is going to “buffer”. In other words, this is when the pH will reach its lowest point and then buffer back up until it reaches its final pH.

Buffering occurs because, as cheese ripens or ages, the hydrogen ions in the cheese displace the calcium ions and “disappear” or are absorbed into the cheese matrix. This causes there to be less free hydrogen ions in the cheese and therefore raises the pH. To track the cheese’s buffering and pH history post manufacture, typically the pH is taken at 24 hours, 1 day, 1 week, 2 weeks, 4 weeks and 6 months. Of course, there is a lot of variation considering the type of cheese being made.

The cheese pH history post manufacture will help indicate if anything is going wrong with the cheese. For example, if making a Blue cheese, the lowest terminal pH will be around 4.6 and then buffer up to a pH of about 6.0. If the lowest terminal pH drops to 5.0, it’s going to be a different cheese in terms of flavor and texture; it will ripen faster.

Strategies to Control Moisture Content
Like acid, cheesemakers need to monitor and control the moisture content of the cheese. Moisture content impacts the quality and safety of the cheese and even a small change (±1%) can have a negative impact on the final cheese.

Typically cheese with too much moisture will have a weak body and pasty texture. There may also be food safety concerns because more moisture results in a higher water activity ($a_w$), which results in more microbial growth (bad) and an increase in proteolysis (good/bad depending on cheese type).

Cheese with lower moisture levels will result in a hard, firm, corky body and texture. These cheeses have lower $a_w$ and higher salt-in-the-moisture-phase resulting in decreased microbial growth (good) but also less proteolytic activity (bad depending on cheese type).

Depending on the milk composition, you may need to adjust the moisture content. “As your milk changes, other parameters change you’re going to have to change your moisture content to match that,” Johnson says. For example, if you have higher levels of fat, you will need to adjust moisture level down to compensate for that otherwise you might get pasty, weak bodied cheese. Of course, different cheeses require different moisture contents. The make for an aged Cheddar is different than a young Cheddar. For an aged Cheddar, the moisture content needs to be 35-37% (depending on how long the cheese will be aged) to give the cheese the best chance to develop correct body, texture and flavor.

Strategies to Influence Moisture Content
Pasteurization: Influencing moisture content can start way back at pasteurization. For instance, pasteurization at 161°F will not significantly denature whey proteins and will produce a lower moisture cheese. However, pasteurization at 166°F will begin to denature whey proteins, which will bind or retain water and produce a higher moisture cheese.

Culture Selection: Different cultures will also influence the final moisture of the cheese. Culture types and even strains within the same genus and species differ in their ability to retain or drive out moisture. For example, Sommer said when he worked in a dairy plant, he knew that certain cultures would produce cheese with a higher moisture content. So, he’d use cultures that retain more water for higher moisture cheeses like Monterey Jack and cultures that drive out more moisture for lower moisture cheeses like Cheddar.

Add Water: Another strategy to make a higher moisture cheese is to add water to the milk in the vat. This will reduce whey expulsion, resulting in a higher moisture cheese. This strategy is more common in Europe, but if you’re a small artisan producer who is not concerned about whey quality this might be a good option.

Add Calcium Chloride: The addition of calcium chloride to the milk in the vat will improve whey syneresis (moisture expulsion) and result in a lower moisture cheese. However, this is not a good option if making aged Cheddar or Parmesan because if you add calcium chloride, you add less rennet and rennet is important in aged cheese because it contributes to the proteolytic activity that is crucial to the cheese aging process and flavor development. Adding calcium chloride is a better option for higher moisture cheeses like Colby or Monterey Jack because then less rennet is needed and you don’t want excessive amounts of proteolysis in those varieties.

Cutting the Vat
The firmness of the curd when the vat is cut influences moisture content as well as fat loss. “Not all cheese varieties should be cut at the same curd coagulum firmness,” Sommer says. “This is part of the art and skill of cheesemaking”.

Soft Set vs. Firm Set
The firmer the coagulated milk is at cut, the higher moisture of the final cheese. Conversely the softer it is at cut, the lower moisture content. For example, when making a high moisture cheese, like Feta, the curd is cut when it is very firm. “The curd is so hard you can walk across the vat,” Sommer said, it is like concrete. Why? Because they want to retain that moisture in the curd. Low moisture cheeses, like Parmesan or aged Cheddar, are cut when the coagulant is very soft because the cheesemaker wants to lose moisture but retain more milkfat in the curd.

Why is this? When coagulated milk is soft, the openings or pores in the curd are very small. Since the pores in the curd are small, they don’t hold much moisture. And, when the curd is harder, the pores are much larger and hold more moisture.

In addition to impacting moisture, the firmness at cut also impacts fat loss. Cutting the curd when it is firmer results in more fat loss. This occurs because the structure of the casein is more rigid when the curd is firm so it takes longer for the curd to “heal” after being cut. It can’t close the gap and trap the remaining fat, so some of the fat will leak out into the whey, as compared to softer curd, where the casein is thinner and less rigid, and therefore takes less time to heal so it traps the fat in the cheese.

A couple notes about coagulation. The rate of gel firming is:

• Increased by increasing concentration of casein.
• Increased by increasing amount of rennet used.
• Increased by adding $CaCl_2$ (maximum level 0.02%).
• Increased by increasing the temperature.
• Increased by decreasing the pH at rennet addition.

The other important factor to keep in mind when cutting is determining the size of the cubes. This is pretty straightforward—cutting into larger cubes will retain more moisture in cheese and smaller cubes will lose more moisture. So, if making aged Cheddar, you would cut smaller cubes and if making Feta or fresh Mozzarella, you will cut larger cubes.

Measuring Moisture
Typically, when measuring moisture content, you want to have a consistent time point—1-2 weeks if possible (depending on the style) and longer for brined cheeses because you want to have the cheese reach equilibrium before you sample it. To get accurate, consistent results, you need to take a representative sample and it’s best to sample the cheese when cooled. Also, if possible, it’s best to send a representative cut portion to the lab compared to a plug.

An inexpensive and easy option is to measure moisture using a forced draft oven (see Standard Methods for the Examination of Dairy Products, procedure 17.054). In this procedure, the first step is weighing the sample, then placing it in an oven for several hours or overnight, and then weighing it again when it comes out of the oven to determine the moisture content. The loss of weight after heating is used to calculate moisture content of the sample.

In Summary

• Keeping the moisture content in the proper range is critical to achieve the correct cheese flavor and texture.
• Rate (speed) and extent (range) of acid development determines calcium retention and cheese body, texture and performance.
• Everything is connected especially acidity and moisture. If you make an adjustment in one step, it will impact other areas and/or characteristics of the cheese.

“Cheesemaking is a holistic process—you change one parameter like moisture and you’re going to change another like acidity, which will result in changing the body,” says Sommer. “That’s where the artisanship of cheesemaking comes into play”.