Filtered bright and unfiltered hazy lager beer samples were either treated
with high hydrostatic pressure (200, 250, 300, 350 MPa for 3, 5 and 10 min at 10° / C
and 20° / C) or conventional heat pasteurization (60° / C for 15 min).
Treatments did not affect ethanol, extract, fermentation degree, density and
pH in comparison with untreated beers. Both treatments produced
microbiologically stable products. Bitterness, color, protein sensitivity and chill
haze parameters were affected by both the HHP and heat treatment.
A storage period of 56 days showed that HHP and heat pasteurization had
similar results in terms of pH and color. However, HHP treated samples had lower
bitterness and protein sensitivity and higher chill haze values than the heat
pasteurized samples which indicates HHP treatment had a positive effect on
bitterness and protein sensitivity at the end of the storage period. The
microbiological stability of HHP treated beers was comparable with heat-treated
beers, and the development of both lactic and acetic acid bacteria was inhibited for
56 days of storage.
Unfiltered beer samples had 7. 48, 7.15 and 2.64 log10cfu/ml of total yeasts,
total aerobic and lactic acid bacteria counts, respectively. No colony formation of
lactic acid bacteria was observed when the samples were pressurized at pressures
equal to or higher than 300 MPa at 10° / C and 20° / C for 5 and 10 min. Total aerobic
and total yeasts counts demonstrated more than 6 and 7 log-cycle reduction when
pressurized at 350 MPa at 10° / C and 20° / C for 10 min, respectively. Heat treatment
gave similar results in terms of log reductions as HHP.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/1098656/index.pdf |
| Date | 01 January 2003 |
| Creators | Buzrul, Sencer |
| Contributors | Alpas, Hami |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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