"Acidity of Honeycrisp – Key to Eating Quality and Competitiveness of Northeastern Apple Growers"

During the past decade, HC has continued to be the number one sought-after variety by consumers in the US. Until this crop year, demand and premiums have remained well above all other varieties, from grower returns to retail sales. Although all of the major apple-producing states have continued to plant, the low yield and low pack out of this variety continues to be a challenge for all of its growing regions in the US and Canada. Rootstock selection, microclimate, a high biennial bearing index, bitter pit, and multiple storage disorders are not even the full list of problems. With the overproduction of most commercial fresh market apple varieties, prices from the fall crop of 2023 through spring of 2024 have been low, across the region and in nearly all varieties. While HC returns have typically been as much as 3 ½ times higher than other varieties, it has fallen to levels dangerously close to the cost of production. If the “day of reckoning” has arrived, then researchers have to up their output at a higher level to ensure all loss and waste of this premium variety is minimized. 

In addition, increased production has also led to consumer dissatisfaction with fruit flavor. HC in the market can have crisp texture but disappointing flavor. The bland flavor has been associated with acidity – despite HC being a sweet fruit, acidity is the underlying positive flavor component. The challenge for the industry is to improve the flavor profile of this much wanted variety, especially with new club varieties entering the marketplace. Early research by Dr. Jim Mattheis (USDA Wenatchee) found that higher acidity at harvest was associated with higher acidity and better flavor after long-term storage. 

Determining harvest maturity at the correct timing for HC has proven difficult and inconsistent. In most varieties tested in maturity programs, internal ethylene concentrations (IECs), as measured in ppm by a gas chromatograph, can be correlated with maturity. In most varieties, the start of measurable (0.2-0.5 ppm) IEP signals the start of the ripening phase, in which the fruit are very near harvest for long-term, controlled atmosphere (CA) storage. In addition, there can be a steady or exponential rise in IEC in which fruit can become overmature and unsuited for CA and must be packed and marketed quickly. In HC, IEC does not correlate with maturity. There is no correlation with when to harvest for any storage regime, length, or marketing window using IEC in HC. Currently, a number of other quality indicators are used to try and determine ideal harvest timing for storage/market destination. One of the primary harvest indicators used in HC is color. In concert with acceptable flavor, color that “jumps out” when the yellow background color makes the red appear almost fluorescent/iridescent is ideal. The major flaw with using color is that weather patterns in the days/weeks prior to maturity can affect proper color. For instance, cooler and cloudier weather patterns can wash out existing color or cause poor color development altogether. Another quality indicator that can help time harvest is firmness. Again, weather patterns during a large part of the growing season or close to harvest can affect firmness.  Above average precipitation can cause fruit to be softer than target levels for CA storage. Drought or below average precipitation can cause fruit to be firmer than normal, and trick growers into harvesting too late if they are waiting for firmness to get into target range for a “normal” season. SSC (%), measured by a refractometer, indicates the overall sweetness of the fruit. As with the above quality indices, weather patterns can affect the SSC and perceived sweetness and flavor. Above average precipitation can cause fruit to have lower SSC and not taste as good. Conversely, drought or below average precipitation can cause fruit to have higher SSC than normal, and make for sweeter tasting fruit. Another quality indicator to help time correct harvest dates is the starch pattern index (SPI). A sample of apples are cut in half, and sprayed with an iodine solution. The conversion of starches to sugars causes the purple-colored iodine solution to turn ripe. Varying stages of ripeness (variety specific) show patterns in the fruit. At Cornell, we use a score of 1-8, with 1 being completely unripe (purple) and 8 being completely (over)ripe (white). Each variety (X) has a set standard (1<X<8) between for suggested harvest from on the early side (midterm to long-controlled atmosphere (CA) storage) to later harvest (to be packed relatively quickly and stored short term in regular air). While SPI can be a guideline to when to harvest for a planned storage/marketing plan, weather patterns can also swing it out of alignment with other maturity/quality indicators. For instance, a droughty season can cause a small amount of carbohydrates to be deposited into the fruit. When these fruit enter the maturation phase, the conversion of starch to sugars happens relatively quickly, and is not a great indicator of when to harvest and does not reflect true maturity. Another relatively new way to help gauge maturity is the delta absorbance (DA) meter. The loss of chlorophyll in the peel can be an effective indicator of fruit ripening. This vis–NIR portable spectrometer measures delta absorbance. It provides a non-destructive relative chlorophyll content index (Ziosi et al. 2008). Absorbance of radiation of wavelengths 670and 720 nm is converted to absorbance based on the Beer–Lambert Law and the index of absorbance difference (I_AD) and represents the absorbance peak of chlorophyll-a and the background spectrum, respectively. The lower the number, the more mature the apple is (less chlorophyll remaining). Past research has shown that DA readings in our region for HC are often not in alignment with other maturity/quality indicators. Therefore, we aim to show that TA will be a tool in the toolbox that can be most in alignment with good eating quality. This is turn should increase farm income for growers of HC in the Northeast region of the US and Canada.