How to Tell if Your Dairy Products Have Gone Bad

    Published: 06-16-2009
    Views: 71,366
    Christine Bruhn, Center for Consumer Research at UC Davis, provides tips on how to tell if your dairy is past its prime.

    Christine Bruhn: I am Christine Bruhn, University of California, Davis. We are talking about how to tell if your food has gone bad and we are going to be focussing on dairy products. The main thing on dairy products is to check the date and keep the product cold. So when you are buying your milk products, the date is usually, on the front of the plastic or it is on the gable part of a carton and most manufacturers will guarantee the safety of their product for 7-10 days after that date. That's if you keep it cold, so be sure to store it in the cold place of your refrigerator and don't leave it out on the kitchen table while you are eating. Pour yourself your serving and put it back in the refrigerator. Now there is one variety of milk that lasts longer and that's the milk that has been ultrahigh pasteurized, ultrahigh temperature and these come in special cartons. You might even find them in the shelf-stable part of the grocery store, that is they do not need to be refrigerated. They are in heavy plastic that even has a layer of aluminium foil to prevent any bacteria from going through the plastic and contaminating the product. These have several months of shelf-life on them. Again, they have a date on the top. Once you have opened it, you have got to refrigerate it, but prior to opening, you can keep that at room temperature just as you have purchased it that way. When you are in the supermarket, you will see that some products come in plastic and others in paper. Consumer really likes the ease of picking up the plastic, but you got to be careful because this product can develop a flavor change that also impacts nutrition. If the plastic is right under the light or if you have left it out in the sunshine, the light will induce a flavor change, kind of like burnt cabbage and it is really yucky. This one is still okay, but that flavor change also impacts the Vitamin-B, the Riboflavin. So paper or plastic, if you are choosing plastic, be sure that you keep it away from the light and don't get those cartons that are just underneath the light. Now what about some of these cultured products, the ones that have the wonderful Lactobacillus bacteria in them? That could be yoghurt, cottage cheese, sour cream. Again, they have dates on them. Once more, 7-10 days past the date is usually just fun. But what about once you have opened the product? This is sour cream that has been opened and you see there is some liquid that has separated out from that product. It is not an issue, really. It is kind of a normal thing that happens with sour cream or with yoghurt. Just stir it back in. You will also see on this particular package that the last spoon that went in had some tomato sauce or something on it. You see a little bit of red. It is really better to use a clean spoon before you dip into the sour cream because now this has been contaminated. It is actually not a safety issue here, but what you will find when these types of products have gone bad is mold growing and you will see spots of mold. Often, they are yellow, but they can be white growing on the surface of the product. These don't have any of that mold, but I would remove the top of that product that has the tomato residue. Now the time when mold is good is when you have a mold ripened cheese like this blue cheese. That is going to taste great and if it has got a little bit more mold on it than the original, it is going to taste even better if you like blue cheese, which I love. Sometimes you can find mold growing on a hard cheese like this, a particular white cheese. This mold is not part of the flavor characteristics of the product and really should be cut off. You need to use a big knife, you need to cut fairly deep because even mold is on the side there, you want to cut off a quarter to an half-an-inch of this product and remember that when you are cutting, you could be contaminating the edge of your knife with mold. So periodically, wash or wipe off your knife so that you don't re-inoculate the surface of your cheese with this mold. Wash your fingers too and I even wash the cheese. You want a nice, clean cheese like this one with no mold showing. You might be buying some of the pre-grated cheese and again, look for the date on this product, it is right here in the middle. Once you have opened these products, use them within a fair amount of time. Again, five days, ten days, maybe two weeks depending upon how clean your refrigerator is and how clear everything is. Don't worry so much about the little white you might see on some of this grated cheese, it is probably the powder they add to keep this cheese from clumping. If you see the cheese having a white part that's kind of growing like a water spot, well, that would be a sign of mold. Next, we are going to talk about how to tell if your leftovers have gone bad.