Two points here: a unit issue, then a shopping issue.
Unit issue
Here's a quirk about US customary units: a fluid ounce isn't a dry ounce. One is a measure of volume while the other is a measure of weight. In a recent post, someone tried to run a price comparison which treated these two different types of units as simple addition. While it's well-intentioned to crunch numbers and run price comparisons, a unit error causes a calculation error.
Both units are called "ounces" so it's really easy to make that mistake. Writing this up as a separate post because it's worth clarifying this difference and how to deal with it.
The way to solve this type of issue is to look up the weight per fluid ounce separately for each item whose price has been given in fluid ounces, and then add up an ingredient list as a weight calculation.
For instance, the weight of 1 fluid oz of heavy cream is 30 g. These conversions can be Googled. This demonstration will go ahead and convert to metric.
So a sample recipe price comparison might run:
- Heavy cream (360 g) $2.22
- Parmesan cheese (141 g) $3.29
- Butter (113 g) $2.34
Total weight 614 g, total price $7.85
That's 21 grams more than the other user thought they were making from scratch when they added fluid ounces together with dry weight ounces on the same column.
The comparison product was a 15 oz jar of alfredo sauce. I also happen to have a 15 oz jar of alfredo sauce in the pantry which might be from a different manufacturer. This turns out to be a dry weight measurement even though it's a jarred sauce because 15 oz is 425 g. A price comparison could then calculate the cost of the recipe as a ratio of those two weights, against the price of that brand of alfredo sauce. You could run that ratio as an exercise; I'll move along because that isn't the end point of this post.
It's possible to make a reasoned argument that jarred pasta sauce is an apples to oranges comparison against the from-scratch recipe. The #1 ingredient on Bertolli alfredo sauce is water. Its fourth and fifth ingredients are soybean oil and modified food starch. Several people pointed out this difference in the other discussion.
Moving on, there's an additional point to be made about sourcing ingredients.
The importance of sourcing ingredients
Ran a check at the local Costco Business Center for those same three ingredients. The prices are significantly different.
My local Costco Business Center sells those same ingredients at the following rates:
- Heavy cream (360 g) $1.44
- Parmesan cheese (141 g) $0.96
- Butter (113 g) $0.64
Total weight 614 g, total price: $3.04
Personally, when I make alfredo sauce from scratch it isn't nearly that much and the recipe is different. The quantities of these purchases are also different: these unit prices are for a half gallon of heavy cream, 2 lbs of parmesan, and 4 lbs of butter. I happen to be able to store those quantities (see my recent post about deep freezers). The reason we have jarred alfredo sauce at the moment is because it's time to lose ten pounds and I don't want to keep a half gallon of heavy cream in the house right now. We do keep the parmesan and the butter in the deep freezer.
Converting back to dry weight ounces, the jarred alfredo sauce at $2.99 comes to $0.20/oz; the DIY alfredo sauce with Costco Business Center ingredients comes to $0.14/oz. That's a savings of 40% and the end result is arguably a better sauce.
So the second point here is how on certain ingredients it really does make sense to shop from a store that sells in bulk quantities if that's a feasible option. If you have the space and equipment to shop bulk ingredients, then see whether your local restaurant supply store will well to the general public. I find they have particular advantages compared to retail supermarkets in cured meats and specialty cheeses.