How much fish do you get in the can? When we drained off the liquid and weighed the fish we found a few surprises.

The two pouches were 100% fish, with no liquid to drain off. But for cans the proportion of fish ranged from a generous 89% (BI-LO Chunk tuna in vegetable oil) to a mingy 60% (JOHN WEST Tuna in brine chunk style). The ‘no name’ supermarket brands were just as likely to be well filled as the more expensive brands.

Labels now often give the percentage of fish (it’ll be mandatory for manufacturers to provide this information after December 20 this year). The drained weight’s a bit more than the actual weight of fish because some of the liquid’s always retained, especially when it’s oil and especially when the fish is in small pieces. So we weren't surprised to find most cans had more fish than the label claimed, sometimes a lot more (see Table).

But there were six products that had less, and two of these (JOHN WEST Tuna in brine, chunk style and JOHN WEST Tuna in springwater, chunk style) more than 5% less.

Testing the taste

Two food technologists assessed and rated the tuna in each can for both flavour and appearance. While they found all of them would be OK for cooking, most people would probably prefer the milder, less fishy brands for sandwiches and salads.

Like chicken, tuna has light and dark meat. Top-quality canned tuna should only have the light meat. The dark meat, which has a stronger, more fishy flavour, is used mostly for pet food. Some cans had more dark meat and tasted fishier.

On the whole, the more you pay, the more likely you’ll get top-quality tuna - but we found some notable exceptions. OCEAN RISE Chunk tuna in brine and BLACK AND GOLD Tuna in brine were among the cheapest but rated well for flavour and texture.

Some of the tuna we opened had ‘off’ flavours. While the tuna was safe enough to eat and might taste OK if cooked, it wouldn’t be so good in a salad or sandwiches.

Off flavours are a sign of poor quality control. Tuna are often caught long distances from where they’re processed. They’re frozen at sea and should be kept cold enough until they’re canned to prevent any spoilage. But without good temperature control rancid flavours develop and bacteria can grow. The canning process ultimately kills any bacteria, but retains the histamine that’s produced as the fish decomposes as well as any rancid off flavours.

According to the international standard, the histamine level in canned tuna shouldn’t exceed 200 mg per kg. Fortunately none of the tuna tested came anywhere near this level. Only two had detectable histamine - both less than 20 mg per kg.

This article last reviewed April 2006