Prior to running these calculations, I advised users to look at the cost of the individual ingredients vs. plain yogurt itself. What you will typically find is that you can get a half gallon of milk for the same price as a quart of yogurt. Yet the only ingredients in a good quality plain yogurt are milk and active cultures. So why does the price double when milk becomes yogurt? Is it the active cultures? Certainly not. It must be all of that heating and energy cost, right? Let's have a closer look.
It's All About the MilkFor my homemade yogurt I use a half gallon of milk from a local dairy which costs me $3.69. Now these cows are grass fed on a family farm, and given no antibiotics or hormones. I doubt you could even find a yogurt on the market that uses milk of this quality. So plug in a suitable number for the milk in your area. Just remember that the better the quality of the milk you use, the better your yogurt will be.
Get CulturedSo if you are making a batch of yogurt using your previous batch as a starter, your cost here is exactly $0. But let's say that this is your first batch, or you are starting over because your starter has become weak. 3 Tbs. of Dannon plain yogurt will set you back $0.16.
All That Heat and EnergySo if the store-bought yogurt is actually a better deal - compared to making your own - the cost of heating the milk to 185 F and then incubating it on the heating pad for seven hours is going double the price of the milk and starter cultures. I have to admit that I had no idea how to calcuate either. So I pulled out my utility bills, and hit the interwebs.
Let's first tackle the natural gas to heat the milk to 185F. If you've watched my videos, or made yogurt yourself, you know that it takes about a half an hour to take the milk from room temperature to 185. I accomplish this by turning my largest burner on high for the entire half an hour. In the manual for my rangetop, I learned that the input for that burner on the highest setting is 12,000 BTU per hour. Great! But when I look at my gas bill, I am being charged in units of one hundred cubic feet (CCF) of gas. Fear not, this gas usage conversion involves a very basic formula. One cubic foot of natural gas contains about 1,031 BTU. Therefore I divide 12,000 by 1031 and get 11.63 cubic feet. But remember, my bill is based units of 100 cubic feet. So I need to divide that figure by 100, and arrive at 0.1163 CCF per hour for my burner. Since I am only using the burner on high for a half an hour, that is 0.058 CCF. Finally, my natural gas provider charges me $0.819 per CCF. Rounding to the nearest penny, that is $0.048 (less than a nickel). Not exactly breaking the bank there either. But, there is still the electricty to consider.
Many users of my site have written to me saying that they don't use a heating pad to incubate their yogurt. This is either because they don't own one, or they can accomplish it with a thermal approach involving a cooler and hot water bottles. I have even heard of using a solar oven, which is basically a box with a clear lid on it, set out in the sun. I find these techniques inconsistent and cumbersome, and prefer the heating pad. But what is this preference costing me? This one is dead easy, using this electricity usage calculator. My heating pad uses 50 watts and my provider charges me $0.11 per kilowatt hour, which is $0.0055 per hour. So over the course of the seven hour incubation, it is costing me $0.04, rounded to the nearest penny.
Survey Says!So if you are keeping score at home, you already know how much it is costing me to make my yogurt. But, endulge me just the same:
So I can make a half gallon of super high quality yogurt, with no added ingredients, for $3.94 per half gallon, or $1.97 per quart. As I have already stated, I doubt you could find any store-bought yogurt using milk anywhere near the quality I am using. I suspect the best large-scale option would be Stonyfield Whole Milk Organic Plain Yogurt, which at present will set you back about $4 per quart. Another way to look at it would be to use your store brand milk, which is probably about $2.50 for a half gallon. That would bring your homemade yogurt cost down to about $1.38 per quart. Compare that with Dannon Plain Yogurt, which is probably about $3.30. Do you see the pattern there? Rendering milk into yogurt effective doubles the price when you buy store-bought. But where is the value added? All they are doing is heating the milk, adding cultures, incubating, and then chilling. When I do this at home, it adds exactly $0.25 or ~6% to the cost of the milk. So what about the other 120% associated with the store-bought stuff? It's called profit - or if you choose to make your own - savings. Your choice.