As a cheesemaker, if you have a vat where absolutely no acid production takes place, then most likely, you have a bacteriophage infection in the bulk starter tank.
In this scenario there really isn’t anything that can be done to salvage the cheese.
However, if you have a vat where acid development slows or stops, you probably have a case of the bacteriophage killing the culture in the vat. In this case, you can get a different strain of starter culture and add it to the vat in an effort to jump start acid development. Another option (time permitting) is to simply let the vat sit until the pH drops appropriately. Of course, the best option is to take precautions to minimize and control bacteriophage in the first place.
Bacteriophage can enter the plant in a number of different ways. People can bring it into the plant (incorrect traffic pattern, dirty uniforms, boots). Raw milk can harbor bacteriophage especially when milk trucks are also used to haul whey products.
Residual starter residues, if not handled correctly, can also contain bacteriophage (properly clean out and discard used bags/containers of starter culture). It can also be found in milk or whey residues on or near cheese vats.
Unclean, dirty equipment, including milk tankers that also haul whey products can have bacteriophage. Not having proper airflow and filters (HEPA) can also spread bacteriophage.
“If I see one thing problematic in plants, it’s air flow,” Sommer said. “Air should flow from high sensitive areas to less sensitive areas.” Without realizing it, plants sometimes create “phage loops” or places where phage is amplified.
Some examples of this include:
- Improperly treated whey cream going into cheese milk.
- Under-heated liquid WPC used as secondary starter solids.
- Cheese vats not on separate CIP system and/or sharing the same CIP system with the belts/towers.
- Phage contamination of incoming milk.
- Using the same pumps and lines to move incoming milk and to load-out whey cream, whey and WPC.
- Hauling raw milk in the same trucks used to move whey products.
Preventing Phage Problems
There are some steps that should be taken to avoid phage outbreaks in your plant. Properly rotating cultures can help keep phage down. This is one reason why it is advantageous to purchase cultures from one culture house. Culture houses will have culture rotation schedules available that are designed to avoid phage outbreaks.
Additionally, limiting the amount of a specific culture used at one time can help keep phage outbreaks down. The number of vat fills per culture blend varies between plants and is dependent on different factors such as air flow and sanitation.
For additional information: you can also read “Understanding and Preventing Bacteriophage,” Dairy Pipeline, Volume 29, Number 2. R The U.S. Department of Agriculture (USDA) selected the Center for Dairy Research (CDR) and Wisconsin