## 1 Introduction  
Cider consumption over the past two decades in the United States has seen substantial growth. From 2010 to 2018, consumption of specialty beverages, including cider, grew 487%, and in 2018, represented an industry worth USD 2.2 billion in the USA [1]. Although most commercially-produced cider is still fermented from imported apple juice concentrates or processing fruits (fruit that did not make it for consumption sale) [1], the demand for beverages crafted naturally and locally is high [2]. Before Prohibition, southwest Colorado, USA, had a diverse population of apple varietals used for fresh consumption and cider production. The Montezuma Orchard Restoration Project (MORP) has documented 436 apple varietals planted in Colorado prior to 1930 [3]. MORP is working with local orchards to restore Colorado's rich history in cider production by genetically profiling apple trees across the state. With an increased understanding of which apple varietals are currently growing in the region and what organoleptic cider qualities they produce, cider makers can make informed decisions on selections of fruit to harvest and process to a final product based on measurable chemical characteristics. This work focuses on the Gravenstein apple which is common to southwest Colorado and is considered a quality cider apple [4, 5]. Results reported herein have been added to the MORP cider chemistry database to inform cider makers about the properties of southwest Colorado cider apples. With increased cider consumption and production, cider makers are looking for ways to diversify their products. One such approach that is gaining traction is the use of hops within the cider-making process. Dry hopping is a technique that is commonly used in the beer brewing industry [6]. This process involves the addition of whole cone hops or dried hop pellets to the beverage after fermentation has been completed. Dry hopping is desirable in the brewing industry, because the hops impart appealing aroma compounds without the bitterness or astringency typically associated with hops. Although dry hopping has been well studied within the beer brewing industry, little work has been carried out to understand how dry hopping impacts the aroma profile of cider. Hops have been shown to contain numerous aroma compounds which include esters, ketones, short-chain fatty acids, and terpen [7]. Previous studies have shown that the three most prominent \"woody\" terpen [8] in hops, comprising up to 80% of the total volatile organic compounds (VOCs), are \(\beta\)-myrccene, cyanophyllene, and humulene [7]. The story is not quite this simple, however. The VOCs that dominate the headspace of hops are often quite different from those in the headspace of dry-hopped beer, due to biotransformation and other variables involved in the fermentation process [9; 10]. For this reason, it is important to monitor the aroma development after dry hopping, to differentiate which aroma active compounds were efficiently extracted from the hops into the beverage, and how they may have changed. In this work, we identify when and to what extent these and other aroma-important species, outlined in Figure 1, are incorporated into the cider headspace during cider making and over the dry hopping process. These previous studies suggest that not only the variety of hops, but the timing of key processing steps including cracking and hop addition, significantly alter the identity and concentration of aroma-important VOCs in fermented beverages. Volatile compounds in cider have been successfully analyzed by sampling the headspace above the beverage [11]. Headspace-solid phase micro extraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) offers a simple and robust approach to analyze cider VOCs that has been used extensively in recent publications [11; 12; 13; 14; 15]. Headspace sampling requires a SPME fiber that will efficiently preconcentrate volatiles of interest.