Essentials of Math in the Kitchen

So, you found an awesome recipe but it isn't written specifically for your needs. Do you need a different number of portions? Do your portion sizes need to be increased or decreased? How about the measurement system, maybe you found a recipe from Canada or Europe and it's in metric units? Maybe some other modification needs to happen. Or, maybe you have to stay within a certain budget. Have no fear...math is here! Unless math isn't your friend, but that's ok, we can fix that because the math isn't very difficult. In fact, it's really about fractions, percent, and decimals. You know, middle school stuff. So, once the videos are up I'll work through each of these adjustments and demonstrate the ease to which this can be done. 

If for some reason this is challenging for you, and for some folks it is (fractions tend to evoke anxiety in a lot of people), there really isn't a whole lot of math that you need to be able to do. Personally, what I do is set my recipes in a spreadsheet and use the metric system so that I can have everything in decimals to make the calculations much easier, and I set up formulas so that there are only a few things I need to do to be able to modify my recipes for different servings or whatever. Keep reading and an explanation of all of these things will be provided for you to follow along.

Convert Recipe Yields

Divide the desired number of servings by the number of servings in the recipe. The decimal from that calculation is multiplied against the amount of each ingredient and otherwise prepare the food as called for in the instructions.

If I want 4 portions but the recipe will produce 8 then I calculate 4/8=0.5 so that I would multiply each ingredient's amount by 0.5 to use the correct amount of each ingredient.

Convert Size of Servings

Sometimes the serving size in the recipe is different than what you want. As if a different number of portions was challenge enough...now the portions have to be a different amount as well. Well...have no fear...math is here and whether you are a math person or not, you too can make this work. Let's say the recipe makes four 8-ounce portions but you want twelve 6-ounce portions.

Step 1:

Start by determining what the recipe produces and what you want the recipe to produce. Knowing this is essential, otherwise you are just guessing and there is no guarantee you will have enough of what the recipe makes, or you might end up with a whole lot more than what you really want and that just represents a lot of wasted money, time, and effort.

So, if the recipe makes four 8-ounce portions        4 x 8oz = 32oz total initial yield.

You want twelve 6-ounce portions                              12 x 6oz = 72oz desired yield.

Step 2:

Approach this similarly as you would convert recipe yields.

Desired yield ÷ initial yield = conversion factor

72oz ÷ 32oz = 2.25

Step 3:

Multiply every ingredient's amount by 2.25 (it doesn't matter if the amount is count, measure by volume, or measure by weight) to get the new amount of each ingredient that you need so that you end up with the desired recipe yield.

Convert Count / Volume to Weight

Essentially, you have to determine this for yourself. There are two ways of getting this accomplished. Option 1 is to prepare the recipe, measuring or counting as directed in the recipe, and follow the instructions as stated in the recipe. But, after you measure each ingredient, weigh the ingredients as you go and write them down. Option 2 is to search online and find out what a cup of this or a tablespoon of that, or whatever our measure or count may be weighs and then write that in your recipe. However, you might find that there is a bit of error in this so I personally don't use this method unless I verify the conversion in my online resource is reliable.

You can also reverse this process if you find a recipe that is measured by weight but you would rather measure. There is nothing wrong with measuring but that is generally more appropriate for smaller recipe yields in the home kitchen. In a commercial food production operation or restaurant weights make more sense because of the frequent recipe adjustments and greater need for consistency in both cost control and quality control.

Convert between the American and Metric Measurement Systems

Have you ever wondered, let's say in science class (I teach this in 6th grade science) why we need to be able to multiply fractions and we use fractions in this way to convert between the American system and the metric system? Well, in the kitchen we need to know how to convert between American and metric systems of measurement. Most of the world, especially European countries, the metric system is used and if you get a recipe from overseas then you will have to use the metric system. More importantly, if you become familiar with the metric system the process of adjusting recipes is much, much, much easier and often can be done without the use of a calculator. You don't need to know any algebra to make this work, just some arithmetic and the conversion factor to convert an American unit to a metric unit.

Essential facts about the metric system:

1000 grams per 1 kilogram             1000g/1kg

1 kilogram per 1000 grams              1kg/1000g

1000 milliliters per 1 liter                 1000mL/1L

1 liter per 1000 milliliters                  1L/1000mL

1 gallon = 3.7854L

1 liter = 0.2200gal

1 fluid ounce = 39.574mL

1 ounce = 28.35g

1 pound = 0.4536 kg

Essential facts about using fractions as conversion factors:

1. Anything that is common in the numerator and denominator of fractions that are being calculated together can be canceled (simplified to the number 1). This fact applies to both the quantity or unit.

2. Set up the conversion factor so that you can cancel the units that you are trying to convert. So, if I were trying to convert from ounces to grams then I would make sure I could cancel the ounces.

How to convert:

I have 12 ounces of sugar and 16 fluid ounces of water. What do I have in metric?

     12oz sugar  x  28.35g = 342g of sugar

              1                   1oz

     16floz water x 39.574mL = 633.184mL water

               1                     1floz

A fun fact: 1mL of water weighs 1g so you can use a scale set to metric system to measure the volume of water. This is unique to water.