How to Determine the Freshness of Oysters

Ah, the perennial question: how long can perishable foods last? We’ve all pondered this at some point, especially while staring into our fridges. Sometimes it’s easy to tell when something’s gone bad – a strange smell, visible mold – in those cases, it’s probably time to toss it. But what about foods like oysters that don’t come with “Best By” dates? How do we assess their freshness without relying on a date?

In our industry, we place excessive importance on harvest dates and marketing, often overlooking the actual freshness of oysters. From a food safety standpoint, oysters stored at the right temperatures can be safe to eat for months. Historically, oysters were stored in pits or cellars during winter and consumed throughout the winter months. Even today, growers use techniques like “pitting” or overwintering oysters in coolers and cellars to protect them from winter sea ice.

At Pangea Shellfish, we define freshness as follows: an oyster that is alive, has an ample amount of liquor, and retains its aroma and flavor from harvest. Based on this definition, there are signs that an oyster has gone bad:

  • The oyster is gaping open, indicating weakness or death.
  • The oyster is dry, suggesting weakness, injury, or imminent death.
  • The oyster smells or tastes different from harvest.

In our experience, oysters usually maintain their freshness for up to 14 days. However, these observations have been largely anecdotal, lacking concrete evidence. To put our assumptions to the test, during the month of May, we decided to shuck one oyster per day and track the changes over time.

A Month-Long Freshness Test

The Sample

For this test, we used a 100-count bag of Salten Rock Oysters from our Blish Point Oyster Farm in Barnstable, MA. We chose this particular oyster because we were intimately familiar with its seed to market process. If any issues arose during the test, we could potentially trace them back to the farm.

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We randomly selected one bag from Lot C-748, which was harvested on Saturday, April 27. The bag was picked up by our company truck and received at our Boston facility on the same day at 4:40 PM. We stored the bag of oysters in a crate, on a shelf, in our cooler for the entirety of the test period. The average temperature in the cooler was 41°F. The oysters received no special treatment – no special handling, no ice or specialized storage, and no wet storage.

We evaluated one oyster per day. Before shucking each oyster, we recorded its size in inches and weight in grams. Once opened, we recorded its temperature, took a photo, and noted its liquor content and flavor. On the last day of the test, May 31, we shucked all the remaining oysters to see how they fared.

Data & Results

Starting Bag Weight: 13.96 LB
Ending Bag Weight: 13.19 LB
Weight Change: -0.77 LB

Bag Yield: 96% (4 oysters dead or dry)
Size Range: 3.0” – 4.0”
Average Size: 3.6”

Figure 1: Weight changes of evaluated oysters per day
Figure 1: The weight changes of each evaluated oyster per day during the test.

Figure 2: Weight distribution of oysters shucked on May 31
Figure 2: The distribution of oyster weights shucked on May 31 (34 days post-harvest). The average weight of these oysters was 56.1 grams.

Figure 3: Photos and notes to assess meat, liquor, and flavor
Figure 3: Photos and notes captured to assess meat, liquor, and flavor.

Discussion of Results

Change in Overall Bag Weight

At the start of the test, the bag weighed 13.96 lb. Over the 34-day period, it lost 0.77 lb (349 g). If we average the weight loss across the bag, each oyster lost about 0.0077 lb (~3.5 g), roughly the weight of two playing cards. This weight loss was expected and well within reason. Over time, the moisture from the outer shells evaporates, and some oysters weaken, losing some liquor in the process.

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Change in Individual Oyster Weights

We initially hypothesized that the weight of each oyster would decrease over time due to expected moisture and liquor loss. However, we found no direct correlation between time and weight. In fact, the oysters evaluated on May 31 (34 days post-harvest) ranged up to 80.9 grams, heavier than any oyster evaluated prior. On the last day, most of the oysters still had visible liquor (see Figure 3).

This doesn’t mean that the oysters gained weight after harvest (which would be highly improbable). Instead, it highlighted a flaw in our testing method. We were just as likely to select the largest oysters as we were to pick the smallest oysters from the bag each week. Conducting a more extensive test or having an oyster “control group” would make the results more reliable. However, as oyster enthusiasts, not scientists, we can say that the oysters we selected each day were of average weight compared to the rest in the bag (see Figure 1).

Change in Smell and Flavor

The oysters evaluated at the beginning of our test easily met our definition of freshness: ample liquor, full meat, and delightful flavor. For the first few weeks, most of the oysters passed our standards, with a few exceptions on May 8 and 10. No significant changes occurred until May 17, 20 days post-harvest. From that point onward, the smell and flavor started to deteriorate. A couple of dead oysters began to emit an unpleasant odor. While the oysters still possessed full meats and liquor, they no longer tasted clean or pleasant. The distinctive, lingering finish was no longer representative of their merroir.

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Conclusions & Considerations

So what did we conclude or prove from this test?

  1. Oysters can be safely consumed up to 30 days after harvest, as long as they have been handled and stored properly. Here’s a photo of me enjoying one of the oysters on May 31, 34 days post-harvest. I’m happy to report that I didn’t get sick and am alive and well enough to write this! However, it’s crucial to mention the importance of proper handling and storage for safe consumption, regardless of the harvest date. Mishandling poses a significant risk for foodborne illnesses caused by oysters, so please do your part.

  2. An oyster can maintain its freshness or quality for up to 14 days after harvest. Our test showed that oyster quality began to decline after 20+ days. While we typically advise customers that oysters stay fresh for up to 14 days, our results indicate that the period of freshness may be longer. However, we prefer to err on the side of caution, so following the 14-day rule of thumb from harvest is generally a safe bet.

  3. Freshness cannot be determined by dates, weights, or visual indicators alone. It’s all about the taste. Before conducting this test, we believed that we could gauge quality by examining an oyster and its numbers, such as dates and weights. However, this experiment demonstrated that those characteristics can be deceptive. Whether an oyster is alive, plump, and filled with liquor or harvested 24 days ago is irrelevant. What matters most is whether an oyster tastes good, and to ascertain that, you simply have to eat it.

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To learn more about oysters and their fascinating nature, visit 5 WS, your trusted source for all things oyster-related.

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