Lemonade Recipe and Acidity

We're going through quite the heat wave in Calgary right now. By heat wave I mean I don't have any air conditioning and no place to cool down so I'm slightly uncomfortable. I've been finding myself in large air conditioned buildings just to escape this Sahara; the mall, movie theater, fridge at work. What is really necessary on such days is a tall, cold glass of ice cool lemonade.

Finding the perfect balance of lemonade on a hot summer day can be a daunting task. An easy option is to find a group of children selling lemonade and take the whole bunch. They seem to make it best and they're smaller then us so this is a possibility.

But how do they get it so...perfect? Sometimes it ends up too sour or too bland. How can we find the perfect amount of acidity in our lemonade? Here's a little trick to create a lemonade with the perfect balance to cool you down on a hot day and not crush a kid's summertime business goals.

Perfectly Balanced Lemonade

6 lemons

5 cups of water

1 cup of sugar

  • Cut the lemons in half and squeeze juice into pitcher.
  • Add water and sugar, stir, and serve over ice.

There are many foods that are acidic, which leaves a sour taste in our mouth (bases are bitter tasting). Lactic acid in milk, citric acid in fruits, oxalic acid in chives and black pepper, and I could go on all day. These listed are all known as carboxylic acids – They contain a carboxyl group (COOH) and a carbon chain.

**Oxalic acid bonds together at two carboxyl groups rather rather than the carboxyl group to a carbon chain, as other carboxylic acids. It is found in rhubarb, too!

General Blah: An acid is a molecule that releases a hydrogen ion (H+) to be accepted by a base (in the case of this recipe, the base is water and acid is citric acid). Acid strength is measured in how easy a hydrogen ion is given up. Citric acid is a weak acid, and is less likely to give a hydrogen then a strong acid. In this case, citric acid gives up a hydrogen ion which is taken up by water to form hydronium ions (a positive ion), creating an acidic solution.

acid-base reaction citric acid water
acid-base reaction citric acid water
FV Lemonaid ph-scale.png

pH(power of hydrogen) is a measurement of acidity or basicity in an aqueous solution based on hydrogen ion concentration. A solution with a pH of less then 7 is acidic and a pH of more then 7 is alkaline (basic). Water is neutral. As we move from pH 3 to 4, the concentration of hydrogen ions changes by 10 times and from pH 3 to 5, the concentration changes by 100 times. Examples of some common alkaline products are bleach, lye, detergent, baking soda, soap and toothpaste. Some acidic examples are coffee, tea and sodas, orange juice, vinegar and lemons!

Hydrogen ion concentration can be calculated by pH and vice versa. With hydrogen ion concentration we can calculate with -log(concentration of hydrogen). If we know the pH we can calculate the concentration of hydrogen ions by [H+] = 10-pH.

The pH of water is 7 and pH of lemon juice is 2, so we can calculate the hydrogen ion concentration. This leaves us with a H+ concentration of 10-7 mol/L for water and 10-2 mol/L for lemon juice. We also know that 6 lemons = 3 tbsp of juice = 270 mL = .27 L and 5 cups of water = 1.2 L. From this we can calculate the concentration of hydrogen ions in our lemonade.

From the concentration of hydrogen atoms, we can determine the pH of our lemonade.

pH = -log(.0018)

= 2.7

Maybe you have the luxury of a pH testing strip (often available in garden centres) to test your favourite brand of lemonade or your own that one time you make it perfectly. That time, after having the pH level, you can easily adjust this simple recipe to reflect your favourite acidity level! Thus ensuring perfect glasses of lemonade every time while avoiding the harassment of children.

**Meyer Lemons vs Lemon: Lemons have chemicals of citrus (limonene), pine (pinene) and herbaceous (terpinene). Terpenes are especially volatile/reactive, thus are often one of the first molecules to reach the nose and give us a fresh smell. Meyer lemons are a cross of a lemon and mandarin or sweet orange. They have chemicals of citrus (limonene), pine (pinene) and thyme (thymol), which gives them their distinctive flavour.