While having one of your cultured products being criticized as lacking cultured flavor is not desirable, those of us who produce cultured dairy products have an even greater fear. Suddenly, the consistent growth of our culture bacteria ceases, and we no longer are producing a cultured product such as cottage cheese, sour cream, buttermilk, or yogurt with the proper flavor, acidity, body, or texture. Even worse, the culture will stop dead in its tracks.

While the production of high-quality cultured products can be affected by the time and temperature of the culturing process, the starter culture may have been infected with a virus called bacteriophage, or phage for short. When phage attacks, it will alter product quality, may delay the process, or cause a complete failure.

Bacteria phage, in fact, can destroy the bacteria that are used to produce quality products. They are smaller than bacteria but are widespread in the environment. The phages that we are most concerned about in dairy products are bacterial strain-specific, but they are capable of mutating rapidly. They attack the culturing bacteria and inject their DNA into the bacteria causing them to become phage manufacturing cells. 

These bacteria cells cause the cell walls of the bacteria to rupture, releasing large numbers of phage particles that prevent the bacteria from producing the desired acidity, flavor, and body in the finished product. Phage activity in dairy products is often indicated by slow sets, difficulty in achieving the proper pH, and changes in the product itself.

Therefore, to prevent a bacteriophage attack in our dairy products, we must control the phage presence. While rotating cultures is a short-term approach to phage in an operation, the long-term solution for controlling and eliminating bacteriophage in cultured products is a robust sanitation program. This sanitation program includes the proper cleaning of equipment as well as the environment itself.

Equipment sanitation

Whether exposed or closed, all vats, tanks, pumps, lines, gaskets, paddles, knives, agitators, etc., must be properly cleaned and sanitized daily and after each use. All parts must be sanitized with a sanitizer at the proper concentration prior to use. Ideally, small parts may be stored in a sanitizing solution. Do not overlook the undersides of equipment, tanks, and vats as these can provide growth niches for bacteriophage.

Environmental sanitation

Just as a strong environmental sanitation program is necessary to prevent the growth of pathogens in our dairy plants, a strong environmental sanitation program is required to control bacteriophage in our cultured operations. This includes the daily cleaning and sanitizing of ceilings, walls, floors, doors, and equipment exteriors. Drains must also be cleaned and sanitized daily. Entrances to the facility must be protected with foam floor sanitizers to control microbial and phage growth.

In addition, a properly maintained HVAC system is necessary to prevent bacteriophage. Phage is capable of becoming airborne so the cleanliness of the system and changing of filters is critical in controlling phage. Maintaining a positive air pressure in the culture and processing rooms is also desirable.

Good manufacturing practices must be diligently followed by all individuals entering the production areas. This includes the use of clean uniforms, hand washing, and zoning of the facility to eliminate unauthorized personnel from entering.

Culture rotation

Facilities will often react to a phage by replacing cultures with those of a different strain, but a robust culture rotation program can supplement sanitation. Culture suppliers have programs for rotation of starter cultures. These programs generally involve monitoring the culture’s activity within the plant and the replacement of a “slow” culture with one of a different phage susceptibility. Often, samples are checked by sending them to the supplier on a scheduled basis.

Bacteriophage can wreak havoc in cultured product operations, but proper management of the cultures used, and a robust sanitation program can go a long way in reducing losses.

Tedd Wittenbrink is technical director at Mèrieux NutriSciences.