Unit 5: The Universal Solvent CH. 7

Importance of Water Water is a nutrient Nutrient – food component necessary to sustain life Other nutrients: Carbohydrates, Fats, Protein, Vitamins, Minerals. Water influences texture, appearance, and taste of food.

Water Structure One oxygen creates a polar covalent bond to two hydrogen atoms. Nonpolar covalent= electrons shared equally Polar covalent= unequal sharing of electrons. Causes regions of opposite electrical charge. Polar Covalent Bond Causes an 104.50 angle between H atoms. Oxygen to have slight negative charge Hydrogens to have slight positive charge

Hydrogen Bonds The negative oxygen is attracted to the positive hydrogen causing a hydrogen bond. Gives water greater surface tension – the force between molecules at the outside edge of a substance.

Surface Tension Surface tension and polarity of water cause cohesion & adhesion. Cohesion: water’s ability to stick to itself Adhesion: water’s ability to cling to something else. *Causes a meniscus

Surface Tension Continued… Increased surface tension makes water have a higher melting and boiling point than other liquids. Results in 3D hydrogen bonding – ice. Hydrogen bonds repel like charges, causing microscopic air holes when ice forms. This causes ice to float because the solid is less dense than the liquid. Not typical that solid phase will float in liquid phase.

Atmospheric Pressure Affects Water Properties Atmospheric Pressure- pressure exerted by the weight of the atmosphere Water at lower atmospheric pressures (higher altitudes) water will boil at lower temperatures & vice versa. Ex) At Mount McKinley (6,194 m above sea level), water boils at 780 C. At sea level, water boils at 1000 C. At the Dead Sea (392 m below sea level), water boils at 1010 C.

Pressure Cookers Have a steam tight seal that builds pressure; therefore, raises the temperature & cooks foods faster. You can also use this method when boiling water in a pot – Placing a heavier lid on a pot will increase the boiling point up to 50 C or 60 C

Water Impurities Impurity – anything added to a completely pure substance. Ex) Salt, Microorganisms, Calcium & Iron deposits from pipes Different impurities cause changes in water’s flavor, color, boiling point, freezing point, and hydrogen bonding.

Water – A Heat Medium Pieces of food suspended in water have little effect on the boiling point of water; therefore, allowing water to boil at a constant temperature. Rapid boil and gentle boil are the same temperature, but does not have the same energy transfer Gentle boil – transfers energy at a lower rate. Potatoes need a gentle boil to prevent breakage. Rapid boil – transfers energy at a faster rate. Pasta needs a rapid boil to prevent the noodles from sticking together

Cooking with Steam Steam is a poor conductor of heat, unless pressure is added as well. Usually cooking with steam takes longer, but when pressure is added the boiling point increases (causing the steam to have a higher temperature) allowing the food to cook faster.

Advantages to Cooking with Steam Steamed foods are more flavorful. Steamed foods are more nutritious. This is because fewer flavor compounds and nutrients are dissolved into the steam than into boiling water.

Steam as a Leavening Agent Steam creates pockets which allows batters and doughs to rise. Steam trapped in the dough is absorbed during cooling. Example) Popovers – thin batter cooked at high temperatures resulting in a light product with large air cells.

Gas-in-Water Solutions Are found in carbonated beverages. Which is the solute? Which is the solvent? Oxygen can also be dissolved in water. Hot water is able to hold less oxygen than cold water. When water is boiled, dissolved oxygen escapes into the atmosphere

Liquid-in-Water Solution Examples Alcoholic beverages: mixture of ethanol and water Vinegar and water: used for pickling Fruit juice concentrates Even though alcohol has one polar area (O–H bond) and a larger nonpolar area (C–H bonds), polar water molecules and the polar area on alcohol molecules are attracted to each other, causing alcohol to dissolve in water. http://www.middleschoolchemistry.com/lessonplans/chapter5/lesson7

Solid-in-Water Solutions In cooking the sugar is usually salt or sugar Added salt or sugar can raise the boiling point and lower the freezing point due to a change in the chemical properties as compared to pure water. Example: Salt in ice cream - creates salt water with a temp below 00C and helps freeze ice cream.

Solid-in-Water Continued… Tea and Coffee: stronger flavors are achieved with more coffee beans/tea leaves or increasing brewing time. Longer brewing time & higher than recommended temperatures increases polyphenols – antioxidants which can add astringency and bite to foods. Maximum flavor will be achieved through proper temperatures (just below boiling point) & brewing times

Water Content in Food Important to know the amount of water in food to understand how the water reacts during cooking and to properly store food. Water Activity (Aw) – federal government measures the amount of water available to support growth of microbes. From 0-1. The higher the # the more perishable the food

Water Content in Foods Continued… Free Water – easily separated (pressed or squeezed) from food. Ex: Some fruits, sour cream Bound Water – water that is bound to the structure of large molecules. Ex: some fruits, meats, vegetables. Hydrate – chemical compound loosely bound with water. Ex: caffeine in coffee Heating a hydrate makes it anhydrous (free of water).

Functions of Water in the Body Maintaining body temperature – sweating Transporting nutrients (minerals and water soluble vitamins) & excreting wastes Water helps break down energy nutrients in digestion.

How much water do you need? You need 6-8 (8 ounce) glasses of water a day. Some people never drink water! Where do they get their water from? Juices, Soft drinks etc. Food Best to drink plain water. Juices and Food are high in sugars and salts, which can lead to obesity, heart disease, high blood pressure, and diabetes.

Thirst Not an accurate warning system. You need water WAY before your body makes you feel thirsty. Not enough water causes: Low energy Reduced coordination Damaged body tissues Ice water relieves thirst faster than warm water! This is because it cools the stomach, causing it to constrict & force water in the bloodstream!

Safe Water Supply Contaminants - anything that causes water to be unsafe – can be found in water. Ex: animal/human wastes, chemicals, garbage, bacteria, viruses, acids, toxins.

Safe Water Supply Continued… Contaminants vary from region to region. This causes issues in the beverage industry. To make a uniform product, companies treat the water beyond the local processing plants.