There’s something special about the Gala apple. Supermarkets stock the variety for 52 weeks a year and many English topfruit growers admit it’s their primary cash cow. In fact, UK Gala production is expected to increase by 40% over the next couple of years. For this reason, AHDB Horticulture has funded research into the potential to extend the domestic marketing period for this popular apple. Dr Richard Colgan, senior research fellow in postharvest physiology at the Natural Resources Institute, led the programme and speaks to Produce Business UK about his findings
Optimising existing practices
With its sweet flavour, crisp and juicy texture and attractive, sunset-red stripes, it’s easy to see why the Gala apple is a star of the fruit bowl. However, as fresh produce buyers know, when these little stars are stored beyond late March or early April they start to compete with their freshly harvested counterparts from the southern hemisphere.
With this in mind, AHDB’s two-and-a-half year research project has sought to discover how UK growers can optimise their existing orchard and storage practices to extend the domestic Gala season and whether they can match the competition.
One of the factors looked at by Dr Richard Colgan was at exactly what point the fruit should be harvested in order for it to store well. He found that growers are better off picking Galas early on in the season because the fruit needs to have a high starch content. “When fruits have a starch content of 85-90% they are still at a fairly immature stage because starch turns into sugar as the apple matures,” he explains.
Dr Colgan worked this out by comparing the quality of apples from six orchards, all of which had been picked from their trees when the fruit had a 60% and then an 80% starch content. The fruit was stored at different temperature ranges – including 0.5-1°C and 1.5-2°C, and under various carbon dioxide-oxygen (CO2-O2) ratios, such as 5% CO2 and 1% O2 or 1.2% O2 and <1% CO2. In addition, the fruit was stored both with and without SmartFresh treatments. The storage temperatures and harvesting regimes that had the greatest potential were further assessed for a second season.
The winning formula
Overall, the study found that Galas harvested with an 85-90% starch level and stored in a 5% CO2 and 1% O2 (5-1) ratio with SmartFresh technology resulted in the best eating quality in April. A taste panel, whose members assessed a full range of characteristics – including firmness, acidity, sweetness, flavour and crispness – rated this eating quality.
Dr Colgan adds that when further tests were carried out in June a ratio of 3% CO2 and 2% O2 with Smartfresh worked best. The research also found that apples with a higher dry matter content – of between 15.5% and 16.5% – had a superior taste.
“We know that good [well-managed] orchards have a high dry matter content,” Dr Colgan says. “These apples tend to be sweeter because they have a higher carbohydrate content in the tissue. Most of the dry matter is actually sugar.”
Differences in scores were less pronounced when it came to rating the optimum temperature for storing apples but Dr Colgan recommends 1.5°C. “There’s a tendency in the industry to store at lower temperatures than this,” he notes. “We are not sure whether this has any benefit in terms of [eating] quality but storing at low temperatures is done [by growers] to reduce rotting. But [that means] they might not have the best quality fruit.”
Matching up to the competition
UK buyers and consumers will be pleased to learn from Dr Colgan’s study that in April some of the [UK] regimes produced “as good, if not better fruit” than imported stocks. However, he adds that in June some of the Gala imports were more flavoursome – although admittedly these were straight off the tree from New Zealand. However, Dr Colgan hastens to add that the English apples were still considered to be of a good eating quality.
“There were more flavour volatiles in the imported fruit,” he claims. “But it’s a different beast and therefore a question of what people want at that time of year. Our [UK] apples are firmer and sweeter. The imported [apples] are less acidic but full of flavour.”
Dr Colgan concludes that the current marketing period for Gala could, in fact, be extended slightly. “We are currently storing Gala until March/late April as a cut-off point, but I think we could go to late April/early May by having these storage regimes,” he reveals. “June might be too far along but late April or early May is OK – although June might be achievable. But whether supermarkets want that is the question.”
Indeed, current trials of the SafePod technology are aiming to further enhance storage regimes for UK-grown Gala apples. [Read this article on Produce Business UK for more information.] While this research continues, Dr Colgan recommends that UK Gala growers pick their crops as early as they can (because of the starch content) before establishing their storage regime as quickly as possible.
Completed last autumn (November, 2015), AHDB’s research into Gala apple storage was carried out in two consecutive phases –TF213 followed by TF221.