In the case of milk, each fat droplet is coated with a layer of milk proteins that prevents the fat droplets from interacting with one another. That’s because the oil droplets interact with one another, a process called coalescence. But after a few minutes, they begin to separate. When you shake up a bottle of salad dressing, the two parts come together. Just like oil floats to the top of water, the fat content in ice cream has a tendency to separate out, as well.īecause ice cream is an emulsion, you would expect that the fat droplets that are present in the mixture would separate after some time, similar to a bottle of salad dressing in which the oil separates from the rest of the dressing. Polar and nonpolar substances do not mix. A polar substance, such as water, has separate regions of positive and negative charge-one end of a polar molecule has a partial positive charge, and the other end has a partial negative charge. Fat is nonpolar, meaning positive and negative charges within the fat molecule are equally dispersed. The problem with using fat as an ingredient in any food is that it doesn’t mix well with a lot of other substances. Fat fills you up, so you don’t have to eat as much to feel full. Most foods that taste delicious probably contain fat. Although fat is frequently vilified, it has its purpose. Reduced fat ice cream does not taste as good as the real thing, and tends to lack the creamy texture. Premium ice creams may have up to 20% fat, which gives it a velvety, rich texture. This cream has a high fat concentration-up to 50%-and supplies most of the fat in ice cream. (You cannot use lard when making ice cream!) Before milk is homogenized, a thick layer of cream rises to the top. Unless it is labeled as light, low-fat or non-fat, ice cream must contain at least 10% fat, and this fat must come from milk. If these same soft drinks were served cold, they would not taste sweet enough.Ī big reason why ice cream tastes so good is because of its high fat content. In parts of the world where soft drinks are normally consumed warm, there is less added sugar. If consumed warm, they taste sickly sweet. You may have noticed this same effect with carbonated soft drinks. If you taste ice cream at room temperature it will taste overly sweet. So more sugar needs to be added to produce the desired effect at the low temperatures in which ice cream is usually served. Cold tends to numb the taste buds, making them less sensitive. Ice cream makers need to add a lot more sugar than you probably realize-usually sucrose or glucose. Milk naturally contains lactose, or milk sugar, which is not very sweet. Other examples of foams are whipped cream, marshmallows, and meringue (as in lemon meringue pie). The presence of air means that ice cream is also a foam. A typical air pocket in ice cream will be about one-tenth of a millimeter across. If you examine ice cream closely, you can see that the structure is porous. In ice cream, liquid particles of fat-called fat globules-are spread throughout a mixture of water, sugar, and ice, along with air bubbles (Fig. Instead, one of the liquids is dispersed throughout the other. Ice cream is an emulsion-a combination of two liquids that don't normally mix together. Due to the high fat content of ice cream, however, and because fat is less dense than water, any ice cream will always be less dense than any aqueous solution, otherwise you would not be able to make root beer floats! Then read the net weight on the label to confirm your observation. The next time you visit a grocery store, compare cheaper and more expensive brands by holding a carton in each hand-you should be able to notice a difference. Better brands have higher densities-up to 0.9 grams per milliliter. A gallon (3.8 liters) of ice cream must weigh at least 4.5 pounds, making the minimum density 0.54 gram per milliliter. The amount of air also has a huge effect on the density of ice cream. One side effect of adding a lot of air to ice cream is that it tends to melt more quickly than ice cream with less air. The less expensive brands usually contain more air than the premium brands. If the volume of ice cream is doubled by adding air, then the overrun is 100%, which is the maximum allowable amount of air that can be added to commercial ice cream. The amount of air added to ice cream is known as overrun.
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