## 1 Introduction  
Tea, a popular beverage, is produced from the leaves of the plant _Canellia sinensis_ (L.) [PERSON]. Tea has been studied for its potential beneficial health effects and has been used for medical purposes in recent decades [1]. Tea may enhance physical health and physiological functions as well as reduce the risk of cardiovascular diseases and cancers [2]. Of the total tea production globally, black tea and green tea account for 78% and 20%, respectively. Black tea is mainly consumed in Western countries and in some Asian countries [3; 4; 5]. The biological activity of black tea is related to its chemical profile [3; 4; 5]. The typical compounds of black tea include catechins, theaflavins, amino acids and alkaloids [4]. The major polyphenic components are catechins, theaflavins and thearubigins. Black tea extract products with an ultrahigh content of theaflavins have been marketed as dietary supplements [4].  
The antioxidant capacity of black tea is associated with brewing conditions, including the infusion temperature, the amount of stirring and straining, and the particle size of the tea leaves [6; 7]. Methods of infusing black tea vary worldwide. For example, infusion of black tea in China involves brewing black tea leaves with hot water at 100 \({}^{\circ}\)C for 20-40 s and repeating this infusion several times. In Ireland,Canada, and the United Kingdom, black tea is mostly prepared using boiling water and consumed with milk and often sugar. A black tea infusion made with a cold steeping temperature (4 or 25 \({}^{\circ}\)C) for 2 h has become popular in Taiwan [8,9]. Determining the optimal method of infusing black tea is crucial to achieving high antioxidant activity. A previous paper reported that the total phenolic content of black tea leaves infused at 4 \({}^{\circ}\)C for 24 h was lower than those infused at 90 \({}^{\circ}\)C for 6 min, and this result correlated with the 1,1-Diphenyl-2-picrylhydrazyl (DPPPH) scavenging activity [10]. Black tea produced using a short-duration, hot water extraction method exhibited the highest antioxidant activity. This result concurred with reports by [PERSON] and [PERSON] [6], [PERSON] et al. [8], and [PERSON] et al. [9]. However, few reports have discussed the effects of the water-tea leaves ratio on the antioxidant activity of black tea.  
A low storage temperature of green tea could considerably extend catechin half-life, and catechins did not undergo significant degradation during a 6-month storage period at 4 \({}^{\circ}\)C [11,12]. The result of optimum storage of green tea at 4 \({}^{\circ}\)C concurred with another report in which no significant degradation of catechin or caffeine was observed during an 8-week storage period [13]. Moreover, no differences in concentrations were observed for the predominant catechins of green tea over the first 6 weeks of storage at 3 \({}^{\circ}\)C in different packages [14]. However, at 25 \({}^{\circ}\)C, the (\(-\))-epi-catechin gallate and gallocatechin gallate of green tea decreased rapidly to zero or close to zero after 30 days; (\(-\))-epigallocatechin decreased by 43% after 60 days of storage, and (\(-\))-epigallocatechin gallate decreased by 68% after 90 days [11]. Both the DPPH scavenging ability and total phenolic content of green tea decreased considerably at 25 and 50 \({}^{\circ}\)C after a 3-month storage period, and they declined further at 50 \({}^{\circ}\)C [15].  
[PERSON] et al. [15] also reported a decrease in the DPPH scavenging activity of black tea after 3 months, but the total phenolic content remained almost constant at 25 \({}^{\circ}\)C, even after 6 months of storage. Besides this example, few studies have reported the antioxidant properties of black tea following short-term storage. To understand the optimal infusion conditions and storage time of black tea before use, this study investigated the effects of the water-tea leaves weight ratio, infusion temperature, short-term storage, and storage temperature on the antioxidant activity of black tea infusion.