To study and understand silage fermentation, there is a need for research using laboratory mini-silos that permit the control of variables and the assessment of different experimental treatments through replication. Research tools, such as mini-silos, are cost effective alternatives that require a small sample size and reduced labor (Solórzano et al., 2016b). Most laboratory silos require manual packing. As an alternative, Cherney et al. (2004) reported the use of vacuum-sealed plastic bags to ensile whole-plant corn. However, it may be possible to use vacuum-sealed glass jars as experimental mini-silos to study the fermentation characteristics of forages. Vacuum packing may allow higher throughput during mini-silo packing and may improve the consistency of packing density. The objective of this study was to evaluate the nutrient content, fermentation and aerobic stability (AS) characteristics of alfalfa (Medicago sativa) silage when ensiled in three different types of laboratory mini-silos for 91 d with or without homolactic bacterial inoculation (HBI).Alfalfa (Medicago sativa) was grown and harvested at a commercial crop farm in Jefferson County, Wisconsin. The whole plant forage was swathed and allowed to wilt to a moisture content of approximately 50%. Wilted alfalfa was chopped to a theoretical length of cut (TLC) of 20 mm and transported to Fitchburg, Wisconsin, for further processing. Particle size distribution was determined using the Penn State particle size separator (Heinrichs and Kononoff, 1996). The proportions of material that remained on the surface of sieves with pore sizes 19.04, 7.85 and 1.27 mm were 47.2, 23.6 and 21.2%, respectively, while 8% reached the bottom pan. One-half of the vegetative material was inoculated using a water soluble HBI at a rate of 1.1 g/t of wilted matter with a product supplying >9.1x10 10 CFU/g containing Lactobacillus plantarum, Enterococcus faecium, Pediococcus acidilactici, Pediococcus pentosacesus, and Lactococcus lactis (MikropHerm WF, Madison, WI) 6 . The other half of the vegetative material received the same amount