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From the Field

Psychrotrophic Sources and Related Bitterness in Finished Cottage Cheese

Sometimes you can pick up a bitter flavor or a bitter note in a container of finished cottage cheese. This defect is undesirable and can be caused by numerous things. These might be the raw milk source used to separate into skim milk placed into the cottage cheese vat. Other sources might be from residual whey left in the cheese curd, from the remaining live cottage cheese bacteria in the curd from the culture strain selected to incubate the cottage cheese, the water sources used to chill and cool the cottage cheese or from the microbial coagulator used to set the cottage cheese skim milk.

Cottage cheese is a fairly bland product to begin with. It consists of curd combined with a fresh cream or low fat dressing. The dressing finishes off the cottage cheese as explained in the last issue. The salt level (which is a flavor potentiator) comes from the dressing as well as any other flavor components such as starter distillate or diacetyl. Other manufacturers use ingredients in the dressing like sweet whey, acid whey or buttermilk. They can incubate the dressing in order to give it a unique flavor (much like sour cream). Below is a brief explanation on what to watch out for if your cottage cheese has developed a bitter flavor.

Residual Whey left in the curd piece – Cottage cheese that is insufficiently washed or cooked too quickly can have whey trapped inside the curd piece (especially with large curd cheese). This trapped residual whey has been shown to contribute a whey taste to the finished product. A bitter flavor can be associated with whey. Manufacturers should be careful not to cook the cottage cheese too fast or too soon, This can cook a shell on the outside of the curd piece. It is best to drive the whey out evenly and slowly from the inside of the curd piece. Cooking too fast and getting a shell on the outside of the curd piece prevents this from happening at the normal cookout temperature. If a shell has been cooked on the outside of the curd particle, sometimes the curd must be cooked 6-10⁰ higher to drive out the whey and firm up the curd piece. Also when washing the whey from the cottage cheese curd, especially in the vat and if the curd is ditched and drained in the vat, be sure not to leave too much acid whey on the curd when washing. This can also contribute to a whey taste.

Culture Selection and the Cooking Step in Cottage Cheese Making – Mesophilic cultures are usually killed by temperatures above 128 - 132⁰F, the cook temperature for small curd cottage cheese. Some newer cultures for cottage cheese include thermophilic organisms that may survive these temperatures. Often with these newer cultures the curd is cooked to above 136⁰F to firm up the curd. This temperature should be enough to kill the thermophiles. Live bacteria within the packaged curd will produce acid which will cause post acidification. Depending on the strain surviving in the curd, it is also possible for proteolytic enzymes to be produced. Bitter peptides are released over time causing the cottage cheese to go bitter. It is true that some mesophilic culture strains (the backbone of the cottage cheese culture) can cause proteolysis in the finished cheese over time. Think of bitter cheddar cheese. This may be influenced by how many mesophilic cells actually survive the cooking process. Generally speaking none survive based on a final cookout temperature of 128⁰F or above. However, if your cookout temperature for small curd is on the low side, say 122⁰F – 125⁰F, then it is possible that some of the mesophilic cultures could survive. One way to eliminate this possibility is to add a small amount of cooking acid in order to keep the curd softer longer during cooking. This will increase the final cookout temperature to say, 132⁰F to make sure all mesophilic culture strains are killed during the cooking step.

The Water Source – Some city water sources can be a source of psychrotrophic bacteria that can contaminate your freshly cooked cottage cheese curd during the rinsing and cooling step. The main culprit here is Pseudomonas fluorescens (see figure 1 below). In order to combat this problem, phosphoric acid and 8-12 ppm of chlorine is added to the cottage cheese rinse water supply to eliminate the possibility of any spoilage bacteria. The pH of the rinse water should be in the neighborhood of 4.5 – 5.5pH to get good microbial control.

Microbial Coagulator – In the past, microbial coagulator received “a bad rap” for contributing to a bitter taste over the course of the shelf-life of the product. This happened because the cleavage points on the amino acid chains of the dairy protein were not specific enough and occurred more randomly than they do today. Enzyme technology has progressed to where we can be much more specific and can cleave the protein at exactly the same point as calf rennet. You can no longer blame the microbial coagulator for contributing to bitterness over the course of the shelf-life in cottage cheese. That’s why when you use a product such as DuPont’s Ziegler 430 Cottage Cheese Coagulator or Marzyme Supreme microbial coagulator; you can be assured you are getting the same reliable performance as with natural rennet. And this at a fraction of the cost! We also sell cottage cheese coagulator in a concentrated form called Marzyme supreme DS. If you need an all-natural coagulator then DuPont’s Marzyme PF 55 is the choice because it is preservative free. If you haven’t looked at these products recently or compared them in cost to your current cottage cheese coagulator, you might be passing up on some huge cost savings!