Two jugs of milk, side by side at the grocery store on May 31: One has a sell-by date of June 11; the other is labeled July 6. What’s the difference?
It’s a modern day supermarket riddle, but one that’s easily solved if you know your pasteurizing principles. The milk with the tighter sell-by date is conventional, whereas the gallon that may still be at the store four weeks later is organic.
But the organic milk doesn't last longer because it's organic; rather, the extended shelf-life is a result of UHT (ultra-high-temperature processing). In other words, it's association, not causation: UHT does not make the milk organic (non-organic milk can be UHT pasteurized and organic milk need not be)—but it does make the organic milk business viable.
But back to the difference in shelf-life: Regardless of whether the two jugs are organic or conventional, the difference in "sell by" date (a reference point more important to shippers and grocery store stockers than consumers—because once your milk is open, even if it’s organic, it’s best consumed within 5 to 7 days) comes down to the way the milk is pasteurized, which falls into two basic processes:
HTST is the "regular" sort of pasteurization, and it’s what most conventional milk undergoes: getting heated to about 160° F for at least 15 seconds. In UHT pasteurization (used to process most, but not all, organic milk), the milk is brought to 280° F for 2 seconds. Both HTST and UHT pasteurization kill, according to Organic Valley Brand Manager Eric Snowdeal, 99% of the bacteria—but it’s the difference between eliminating 99.1% and 99.5%, figuratively speaking—that makes HTST milk "in code" for between 16 to 21 days as compared to UHT’s 55 to 70-day range.
But any type of milk—organic or conventional—can be pasteurized by either method, so why is organic milk generally UHT whereas conventional milk is not?
The answer to that question has to do with buying patterns. Organic milk—which comes from cows that have been raised according to organic farming practices (the animals are never given antibiotics, artificial growth hormones, non-organic feed, or GMO feed, and they must be let out to organic pasture for at least 120 days of the grazing season)—is more expensive to produce, priced higher on the grocery store shelves as a result, and, consequently, turned over less quickly. As Dr. Bill Weiss, a professor in the Department of Animal Sciences at The Ohio State University's Agricultural Research and Development Center, put it, "Organic milk is much more valuable than conventional milk: If it spoils on the grocery shelf, it’s a significant loss."
Extending the shelf-life of organic milk via UHT pasteurization alleviates some of the risk for producers and grocery stores: It's okay if the expensive organic milk shipment isn't bought up as quickly as the cheap conventional milk—thanks to UHT, it stays sellable longer. It's the same reason that, if you look closely enough, you'll see that a lot of creams, organic or not, are also ultra-pasteurized—another expensive product with a slow turnover rate.
"In the early days of the organic industry," Eric of Organic Valley explained, "it was very difficult to go through a case of milk with that amount of code left on it [before it could no longer be sold], so by extending the shelf-life, it allowed retailers to work through [that case] before it expired." A longer shelf-life also enables organic products to reach "retail stores that didn't have enough foot traffic of people looking for organic milk." They can ship the milk greater distances, expanding the distribution of organic products into regions of the country that don't have networks of natural food co-ops.
So if UHT processing extends the shelf-life of milk upwards of three weeks, why not process all milk like this? In much of Europe and Asia, shelf-stable boxes of milk—which only need to be refrigerated once opened—are ubiquitous. In the US, however, “regular milk is generally not [UTH pasteurized] because there’s no reason to extend shelf life; it’s turned over so quickly. And it does change the taste a little—it is different, not better or worse.” According to Scientific American, UHT pasteurization "sweetens the flavor of milk by burning some of its sugars (caramelization)."
When we tasted Organic Valley whole milk alongside Five Acre Farms whole milk (local but not organic), the differences were easy to discern. But while most of us noticed a more pronounced sweetness and distinct aftertaste in the organic milk, no one had a super strong opinion: Even tasters who preferred one over the other said they would not have noticed anything different about the milk had we not been tasting them side by side.
Organic Valley's consumer research has proven that customers like both organic and conventional milk (there's no strong lean either way), which is why they produce both. Since the "organic" label of milk is about the land usage and the animal treatment, not the pasteurization process, there's no reason that HTST cannot be used for organic milk, too—it just means the producer is betting on being able to sell the high-priced organic milk quickly. In areas where the turnover of organic milk is fast (a metropolitan area with a HTST plant nearby and a lot of natural food stores, for example), it’s possible for Organic Valley to provide HTST organic milk without fear of it expiring on the shelves.
Next time you're at the store, take a closer look at the expiration date—but don't read too much into the multi-week difference: Remember that it comes down to pasteurization, and not necessarily the quality of the milk. (But if you're going on a long vacation and looking to stock the fridge with a gallon that'll still be good when you get home, it's a safer bet to go with organic.)
What do you buy at the store? Tell us in the comments!