Spoilage hurdles

Pasteurisation is only effective in conjunction with other factors that make a product inhospitable to contaminating organisms. The numerous hurdles present in beer have a synergistic effect and mean that only mild pasteurisation is required for practical sterility and the effects of heat treatment on flavour are minimised. 

Mashing and boiling during wort production produce the required degree of sterility prior to yeast pitching and the fermented beer has a number of hurdles (Vriesekoop, Krahl, Hucker, Menz, 2012 Table 12.3)  

The ethanol content of beer (generally between 3.5-5% by volume) is a large hurdle to microbial growth. Ethanol inhibits cell membrane functions and induces cell membrane leakage. Increased cell membrane permeability increases the effects of low pH on the cell by increasing proton passage into the cytoplasm and reducing the ability of the cell to maintain pH homeostasis. 

The low pH of beer (generally 3.7. 1) inhibits the growth of many microorganisms. At low pH entry of organic acids into the ceU is enhanced, causing intracellular acidification. This leads to the destruction of enzyme systems and the reduction in nutrient uptake. 

The microorganism will attempt to maintain pH homeostasis by using energy to pump cations across the ceU membrane. When the ability of the cell to do this is overwhelmed starvation and cell death follow. 

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Leistner (1978,1987,1995) has explained the synergistic affects of various treatments, such as salt, nitrite, smoke, and a , on production of IM meats. Some or all of these factors may be involved in providing hurdles that assist in producing safety in IM meats. Further research is still needed to ascertain the role of each hurdle in preventing both spoilage and growth of food pathogens in various IM meat products as pointed out by Leistner (1987). 

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