This is our second week of evaluating fruit for the 2021 apple maturity assessments. We assessed Premiere Honeycrisp on G11 and Firestorm Honeycrisp grafted on B9 (without any plant regulator application) located in the same farm in Smithsburg, MD. In general, Premiere Honeycrisp fruits are ready for spot picking this week, while Firestorm Honeycrisp is far behind yet. As expected, Premiere Honeycrisp advanced it maturity since last week, displaying average starch index values of 2.5, firmness values in the range of 15lbs, DA index values of 0.9, skin red coloration ~40% and soluble solids contents ~12-13%. The information for both cultivars is summarized in Table 1.
Surface color (eye-balling): Premiere Honeycrisp fruits are showing an overall average 40% of red skin coloration, ranging from 20 to 60% coloration, while Honeycrisp fruits displayed values around 5%.
Background color (DA index): Values are around 0.9 for Premiere Honeycrisp, while Firestorm Honeycrisp is >1 still. Readings of 0.60-0.70 are recommended for harvesting fruits for long-term storage, and we observed Premiere Honeycrisp fruit that already was in this range, thus ready for spot picking. An index of about 0.35 is targeted for harvesting fruit for short-term storage (which we have not observed yet). Fruits were measured with a DA meter, a device that measures the absorbance difference between 670 nm and 720 nm light. A higher DA index indicates a larger content of chlorophyll-a in the fruit skin.
Fruit firmness: There were significant differences in firmness between both assessed cultivars. Premiere Honeycrisp fruit are displaying firmness values around 15lbs (ranging from 13-17lbs), while Honeycrisp fruit are showing an average of 21-22 lbs. In general, apples that are destined for long-term storage (>3 months) should be harvested with a firmness of at least 15lbs; while for fruit for shorter-term storage (1-2 months) a firmness of 13-15 lbs is appropriate. For Premiere Honeycrisp we already assessed fruit that is displaying firmness for long-and short-term storage. Firmness was measured with a penetrometer with a 7/16-inch diameter plunger.
Starch content: Firestorm Honeycrisp fruit is at the lower end of the scale (1.0) still, while Premiere Honeycrisp fruits are showing a higher degree of starch disappearance in the flesh around 2.5. It is important to mention that we did observe Premiere Honeycrisp fruit with values around 4-5, ready for spot picking, while others still on the 1.5 range. The common starch index rating system (Cornell chart) on a scale from 1 to 8, where 1 is full starch (all blue-black) and 8 is starch-free (no stain), was used. In general, on a 1 to 8 scale, values ranging from 4-6 are recommended for harvesting apples for long-term storage, while 6-7 for fresh market.
Sugars and Acids
Soluble solids contents (SSC): SSC values, measured with a portable refractometer, are showing that Premiere Honeycrisp fruit increased their values and are averaging 12-13%, while Honeycrisp is around 11%. In general, it is recommended to harvest fruits with readings around 12% to 14% SSC, another reason why spot spiking Premiere Honeycrisp this week is recommended.
Acidity: Our results show that Premiere Honeycrisp decreased it acidity values since last week to ~0.8%, while Firestorm Honeycrisp fruit was ~1%. A decrease in acidity content is an indicator of advancing maturity, reason why this indicator is included in this report. Acidity was measured with an automatic titrator, quantifying malic acid (the major acid present in the juice of apples).
Table 1 Summary table of maturity assessments for Premiere Honeycrisp and Honeycrisp harvested from Smithsburg, Maryland. Values in parentheses indicate the results from last week’s monitoring.
|Skin Red Color (% blush)
|Starch Index (Cornell 1-8)
|Soluble Solids (%)
|Acidity (% Malic Acid)