Starter Culture Use

Starter Culture Usage in Cheese Production

In this course, information will be given about the properties and use of starter cultures used in cheese production. Since milk is a perishable food, it is processed into a number of products to increase its durability. Cheese has an important place among these products due to infection and intoxication risks, especially zoonotic diseases. For this reason, pasteurized milk is used in cheese production in milk processing facilities today.

In order to obtain standard quality and healthy dairy products, it is important to use high-quality and hygienically obtained milk. For this, it is considered necessary for the milk to undergo heat treatment, that is, pasteurization.

Basic functions of starter cultures:

• Lactic acid formation
• Breakdown of proteins
• Breaking down fats
• Creating flavor and aroma compounds
• Preventing the formation of harmful bacteria

The pasteurization process eliminates harmful and pathogenic microorganisms found in milk that cause the product to spoil. With this process, most of the lactic acid bacteria that allow the cheese to ripen during cheese production are also inactivated. In this case, the production of cheese at the desired level becomes difficult. In addition, heat-resistant bacteria that cannot be activated during pasteurization multiply and exist in the environment, causing various defects in the cheese.

In short, when pasteurized milk is used in cheese making, it is a technological necessity to add lactic acid bacteria, which are destroyed during pasteurization, as pure cultures in order to create the typical aroma and flavor in the cheese. In addition, starter culture addition is needed to achieve a certain level of proteolysis and to keep the effects of some unwanted bacteria under control with antimicrobial properties.

Starter cultures can be defined as “useful microorganisms added to milk to limit the development of harmful microorganisms in milk, to ensure the formation of product-specific taste, aroma, and structure, and to always obtain a product of the same standard and quality.”

Natural starter cultures:

Natural starter cultures are obtained from raw milk of high bacteriological quality, from whey (WW) formed during production, or from a mixture of whey and yeast. These natural cultures were used in cheese production until the beginning of the 20th century.

Although industrial starters are used instead of natural yeast cultures in the production of many cheeses around the world to meet the desired demand and ensure standard production, especially in European countries such as Italy, France, and Switzerland and in South America, PDO (Protected Designation of Origin – Protected Origin Title) natural starters are widely used in the production of geographically indicated regional cheeses.

Today, there are many well-known cheese varieties produced with natural cultures. Some of these cheeses include Minas, Parmigiano Reggiano, Granada Padano, Mozzarella, Emmental, Comté, and Kars Kashar cheese produced in our country.

Natural starter cultures are produced daily in cheese production facilities. These cultures are formed as a result of a set of conditions (heat treatment, incubation temperature, pH, competition, and/or antagonism) applied to raw milk and whey. The aim is to select the strains that are best adapted to the desired conditions.

The microbiological composition of natural milk cultures, the individual experiences, and different practices of the masters working in cheese production facilities in the culture preparation processes may also vary depending on geographical differences.

In obtaining natural cultures (for whey), whey obtained the day before is generally used. A certain amount of this whey is taken and left to rest at a suitable temperature (42-50°C) and time (approximately 18-24 hours) so that the bacteria in it can develop. This culture is referred to as the “thermophilic PAS culture.”

In addition to natural whey cultures, cheese producers also occasionally use natural milk starters prepared from milk. Milk-derived cultures are predominantly used in the production of soft and semi-hard cheeses.

Periodically taken hygiene criteria require high-quality milk to be subjected to heat treatment at 60 - 65 degrees for 10 - 15 minutes and then brought to 45 degrees. Then, incubation is performed at the same temperature to ensure the acidification of the milk.

Thermophilic lactic microflora:

Thermophilic lactic microflora (especially S. thermophilus) in the milk's own flora is increased, i.e., the culture is enriched. When the milk acidity reaches 0.4 - 0.5% lactic acid (after approximately 5-6 hours), incubation is terminated, and the formed curd is added to the cheese milk to be processed the next day. Cheeses such as Mozzarella, Caciocavallo, Asiago, and Montasio are produced with natural milk starters.

In the combination of whey and rennin, a culture with high acidity (1.25 - 1.35% lactic acid) is obtained by keeping dried calf sirloin in boiled whey for a while. These cultures are used in the production of Swiss-type cheeses such as Gruyere and Emmental.

This method is mostly preferred by small businesses. These types of cultures are usually thermophilic and heterofermentative, with Lactobacillus strains being more dominant. These cultures are also called "Unidentified Cultures" because they contain different numbers of species or strains, and their mixtures are not fully known.

In white cheese production, combinations of bacteria such as Lc. lactis ssp. lactis, Lc. lactis ssp. cremoris, Lc. lactis ssp. lactis biovar. diacetylactis, Str. thermophilus, Lb. sake, Lb. casei, Lb. plantarum, and Lb. helveticus are used as thermophilic and/or mesophilic starter cultures.

These bacteria have low resistance to salt, making the search for suitable alternatives necessary. In the production of most cheeses, where fermentation is not done beforehand, selected lactic acid bacteria are added to milk for each cheese variety to initiate lactic acid formation.

In addition to lactic acid bacteria, propionic acid bacteria (Propionibacterium freudenreichii subsp. shermanii), molds (Penicillium camemberti, P. roqueforti), and yeasts are also used as cultures in cheese production. These cultures, containing specific strains of microorganisms, are also referred to simply as "pure cultures."

One of the basic purposes of starter cultures is the production of lactic acid. Through the lactic acid they produce, starter cultures facilitate the coagulation of milk and, most importantly, enable the easy separation of water from the curd during cheese production. Moreover, they help prevent the development of undesirable microorganisms, thus extending the shelf life of the cheese.

This well-organized use of starter cultures ensures the desired structure, taste, and aroma in cheeses. By increasing the level of lactic acid in cheese milk, the amount of calcium and rennin retained in the curd also increases.

During the activity of starter cultures, flavor and aroma compounds such as lactic acid, acetic acid, amino acids, fatty acids, aldehydes, ketones, alcohols, and lactones are formed. Starter cultures show optimum growth at specific temperatures, and the microorganisms they contain are grouped according to their forms (liquid, powder, or frozen) and type (mixed, single, or multiple strains).

In addition to these commercial cultures, natural cultures prepared from whey or raw milk are widely used, especially in countries like Italy, France, Switzerland, and Greece.

Before proceeding to the coagulation phase, the milk acidity level must be brought to a specific pH range (average 6.3 pH - 6.5 pH) after pasteurization. In acidic curds, the milk acidity value is adjusted to pH levels between 4.6 and 6.0. After pasteurization and fermentation, the milk is brought to a temperature of 28-34°C, and additional starter culture is added.

Heat treatment is not an application for bacteriological standardization of cheese milk quality. During heat treatment, many bacteria that aid in cheese maturation are lost, and some enzymes become inactive. Therefore, adding starter cultures after heat treatment becomes a mandatory application in cheese production.

The types of starter cultures used in cheese production vary according to the type of cheese. There are differences between the functions of cultures, and these differences are taken into account for each cheese type, resulting in the creation of specific culture combinations.

For example, in white cheese production, starter cultures such as Str. lactis, Lb. casei, Lb. plantarum, and Lb. brevis are used in various combinations to prepare the desired cheese culture. The acid formation rate of bacterial combinations in starter cultures can vary (slow, medium, or fast).

In general, hard and semi-hard cheeses are produced using slow acid-forming starter cultures, while fast acid-forming starter cultures are used in soft cheese production. The speed and level of acid formation are also controlled by the amount of starter culture added to the milk. For example, in the production of hard and semi-hard cheeses, the amount of starter culture used is between 0.2% and 1.0%, while in soft cheese production, this amount can go up to 2.0%.