A recent study reported tannin content in processing apples grown in Virginia in order to assess their characteristics for hard cider. Despite this analysis of fruit from a single harvest year, the chemical characteristics relevant to hard cider production of commonly-grown processing apples in the Mid-Atlantic region are not widely reported, especially with respect to tannin content (analyzed in terms of total polyphenol content here).
The key chemical characteristics of apples, when considered from a hard-cider making standpoint, include malic acid content, pH, sugar content, and tannin content. A further characteristic, the so-called 'vintage quality' is less well defined and more elusive, but not less important than these other measurable characteristics. Based upon measurable key chemical characteristics and the opinions of several cider makers throughout the U.S. several dessert cultivars such as GoldRush, Jonagold, York Imperial, and others are desirable in blends for cider making, if not capable of producing vintage single-variety cider. The goal of this study was to examine the chemical characteristics of some important processing apples grown in the Mid-Atlantic Region to assess their suitability to production of hard cider. Another objective was to compare these common processing varieties to some dedicated hard-cider varieties and some pollinator crab apples.
Processing apples were harvested at approximate commercial harvest dates at the end of the growing season in 2014. Cider apples were harvested when fruit began dropping from the trees or at reported harvest dates. Several of these varieties do not have published harvest dates relevant to seasonal conditions of the Mid-Atlantic region, so best approximations were attempted. All apples were kept in refrigerated storage for up to 2 months before juice extraction.
Juice was extracted from about 10 fruit of each variety using an Omega J8006 low-speed masticating juicer. For some samples of advanced maturity, pulp and juice were not adequately separated by the juicer and a further straining process through cheesecloth was needed. Some delay in processing pulpy samples likely led to reduced tannin content as polyphenols are polymerized in the presence of polyphenol oxidase enzyme found in apple pulp. After extraction and pulp removal, juice was treated with 5% sulfite solution and kept in refrigerated storage. Soluble solids were analyzed with a digital refractometer and reported in % Brix units. Juice pH and titratable acidity were measured with a titratable acidity minititrator and pH meter (Hanna Instruments, HI 84432). Tannin content is reported in gallic acid equivalents and was analyzed through the Folin-Ciocalteau method.
Implications for growers and cider makers
Tannin content for dedicated cider varieties that were not exposed to pulp after juicing averaged 2,894 mg/L for the sample set, while dessert varieties averaged 439 mg/L. The average tannin content of the two crab apple varieties tested was 12,496 mg/L, or more than 4 times higher than the average for the cider apples. For context, in grape winemaking, white wines typically contain tannins in the 100 to 200 mg/L range, and young red Italian wines typically contain 1,000 to 2,000 mg/L. Cider makers wishing to increase tannin content in ciders in the Mid-Atlantic may make judicious use of existing pollinator crab apples, such as Indian Summer crab apple and Manchurian crab apple, until knowledge of performance of dedicated cider varieties is established for the Mid-Atlantic region.
Chemical constituents of dessert and cider apple cultivars grown in Pennsylvania in 2014.
|Cultivar||Brix (%)||pH||Titratable malic acid (g/L)||Tannin (GAE, mg/L||Tannin:Acid ratio|
|Flower of Kenta||13.8||4.1||2.3||3,285||1.43|
|Indian Summer Crab||22.5||3.2||29.9||15,598||0.52|
|Maslin Pink Lady||15.5||3.24||7.6||313||0.04|
|Medaille D'Or||16.7||4.12||<2.0||4,421|| >2.21|
*Unreported tannin readings for cultivars with an asterisk were lower than expected due to over-maturity of fruits and oxidation in presence of pulp after fruit crushing.
a - Identity of this sample is uncertain.
Thank you to Adams County Nursery, Big Hill Ciderworks, and Three Springs Fruit Farm for donations of fruit. Thank you to the Extension Committee of the State Horticultural Association of Pennsylvania for funding this study.