By Doug Vargo
DuPont receives and inspects the phage reports for all cottage cheese manufacturers using our cultures in the United States. What this does for me is that I can readily see which culture strains are getting hit with bacteriophage. What this does for you is if I feel you are in danger of showing a significant slowdown of acid production by the culture in the cheese vat itself, I will suggest resting that bacterial culture strain for several weeks and replacing it with a different strain (either temporarily or permanently). This keeps your cheese culture incubation times pretty consistent from vat to vat and day to day. (within 15 minutes of one another). If one strain is slower than another by more than 15 to 30 minutes, it might be time for a strain change. What happens when phage does come to visit?
This is where sanitation practices become critical in a cottage cheese making room.
- Keep whey and curd off the floor as much as possible. This just becomes more food (good lactic acid bacteria) for the phage virus to infect. In fact, please be sure to completely rinse all spilled curd and whey from underneath your cheese vats. This may entail a regular program of using a pressurized soap gun to take care of the floor underneath the cottage cheese vats and then flooding the floor with a 200 ppm chlorine water solution to sanitize under the vats and into the drains.
- Watch out for “drips into the vat” from above that can seed the cottage cheese vat with phage or unfavorable bacteria during incubation or after cook when the cheese is dressed or creamed in the vat. Condensation is more of a problem in the summertime due to humidity. Condensation can build up on and drip from overhead air conditioners or chill water lines over the vats. These water drips can contain pathogens, spoilage micro-organisms or phage, and can create off flavors in your creamed cottage cheese. Human perspiration can also be a source of contamination.
- Try to maintain positive pressure airflow from the cheese room to other areas of the plant so air blows out of the room and not into the room. Check and change air filters regularly on the intake side of the room so they don’t act as a seeding spot for phage into the room. At one particular plant they had a slow set of buttermilk when set in one particular pasteurized incubation vat that was located directly under the positive air pressure system intake filter. Changing the filter and cleaning the vent solved the slow incubation problems because they took the “phage seeding spot” out of play! Buttermilk incubation times were reduced and went back to normal as if the buttermilk was set in any of the other setting tanks in the room.
- Keep outside employee traffic to minimum through your cheese room. That means no shortcuts through the room for tank truck drivers or other employees that shouldn’t be in there. Remember people can bring phage and other undesirable bacteria into a room on their clothing or on the bottom of their shoes. Cheese cooks should know the importance of this and keep all unnecessary visitors out of their cheese room.
- Sanitize the atmosphere regularly! This might be a touchy subject because of vapor inhalation, but safety equipment is available to make this exercise a safe and efficient task. This is probably the one most important thing that can be done to control phage. Chlorine fogging the cheese vat room with 200 ppm of chlorine water vapor is sufficient to kill airborne phage if it is present in the cheese room. Eliminating the phage population in your plant is an important solution for getting your cottage cheese cultures growing up to their fastest potential. Remember slow vats happen when the phage virus infects the bacterial cheese culture cell essentially killing the cell while propagating many hundreds more phage in the nucleus of the cell in the process. These hundreds can become millions in a short period of time. If you have experienced vat incubation slowdown on a certain day, or with one particular cottage cheese culture, it might be time for a good old “cottage cheese room chlorine fog”. I don’t know of anything that is more effective in the battle against bacteriophage. Sanitizing and re-cleaning any cheese vats that haven’t been used for several days is also a good practice, just to ensure there is no phage lurking in there before filling with skim.