## 3 What Happens to Samples When They Are Ensiled at Different Stages? The researchers divided the fermentation process of silages into different phases (Figure 3), including the initial aerobic phase, fermentation phase, stable phase, and aerobic feed-out phase [5,6]. The aerobic phase starts from the movement of substrates to inside the silo via the compaction process until the oxygen levels are reduced [5]. This phase has the most notable features, such as increased temperature (>32\({}^{\circ}\)) of samples due to cellular respiration by plants and aerobic microbes. In this condition, the amount of energy generated by respiration is much higher, and this energy can be dissipated in the form of heat. With increases in acidification and concentrations of oxygen, the microorganisms that cannot survive in these conditions are inhibited, but those microbes can have survival properties that succeed. Epiphytic/endophytic microorganisms of plants, possible contaminants, or manually added inoculums are present in this stage. The most common epiphytic microbes are enterobacteria [7], yeast, molds [8], and low numbers of LAB [9,10] with considerable diversity among plants, climates, and forage crop management. Fermentation phase: in this stage, the fermentation process is accelerated by the dominant microorganism. In well-compacted silages with sufficient water-soluble carbohydrates, the LAB can dominate the fermentation process due to their adaptive and competitive growth characteristics, resulting in well-preserved materials. The population and epiphytic diversity of LAB is highly variable and interferes with the process. In general, if LAB dominates the process, lactic acid fermentation has been started; however, it may be varied by the proportion of homofermentative or heterofermentative fermentation as a result of variations in the lactic acid to acetic acid ratio from 1:1 to 6:1 [3]. The duration of  
Figure 3: Phases of silage fermentation at ensiled plant materials. Figure 2: Stages of silage production from different plants. this phase, or intensity of fermentation, highly depends on the availability of substrates and growth conditions for dominant microorganisms. If not, LAB dominates, and a failure to accelerate the lactic acid fermentation and reduction in pH (pH 4.0-4.5) results in undesirable microbes such as _Clostridium_, _Listeria_ spp., and propionic acid bacteria (PAB) starting to grow and affect the silage quality [11]. [PERSON] et al. studied the impact of LAB on the fermentation of Italian ryegrass at different storage periods. Reduction in pH and higher lactic acid content were noted in silage treated with LAB at 45 d and 95 d. Meanwhile, the further extent of storage periods affects lactic acid fermentation due to lower LAB at 180 d and 360 d, resulting in lower lactic acid and higher acetic acid [12]. This may be due to nutrient availability of the forage samples, which favor growth of the other microorganisms. In another study [13], rice straw treated with LAB had almost similar lactic acid and acetic acid contents throughout the experimental periods (45 d, 90 d, and 365 d). This confirmed that the fermentation process is highly based on the availability of substrates in plants. In the stable phase, the reactions are minimal, and the fermentation characteristics of the silages are affected by storage periods. During this phase, the pH of the silage is between 3.8 and 4.0. The storage time affects the pH, lactic acid, acetic acid, propionic acid, and butyric acid, 1, 2-propanediol, the lactic/acetic acid ratio, and NH3-N [12,14]. All chemical and microbiological properties of the silage in the stability phase will affect the intensity of the deterioration after the silo opens. When the silo opens for the feed-out (feed-out phase), the fermented silages are in contact with air, which alters the conservation principles, anaerbiosis, and environmental conditions [5,15].