Alcoholic fermentation in wines. Determining alcoholic fermentation in wine is critical to the wine-making process.

Must/wine density is a good indicator of the fermentation point, since the density value decreases as sugars are converted into alcohol. For decades, winemakers have measured must/wine density with a hydrometer. Although accurate, the hydrometer employs a manual process that is very time consuming. Consequently, large wineries are searching for more rapid measures of density measurement.

An alternative method utilizes the hydrostatic balance instrument (similar to the hydrometer, but digital).

A winery in Portugal collected must/wine density measurements on white wine samples randomly selected from the fermentation process for a recent harvest. For each sample, the density of the wine at 20°C was measured with both the hydrometer and the hydrostatic balance. The densities for 40 wine samples are saved in the WINE40 file. The first five and last five observations are shown in the accompanying table. The winery will use the alternative method of mea-suring wine density only if it can be demonstrated that the mean difference between the density measurements of the two methods does not exceed .002. Perform the analysis for the winery. Provide the winery with a written report of your conclusions.

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Sample Hydrometer Hydrostatic 12345 1.08655 1.09103 1.00270 1.00272 1.01393 1.01274 1.09467 1.09634 1.10263 1.10518 .... 36 1.08084 1.08097 37 1.09452 1.09431 38 0.99479 0.99498 39 1.00968 1.01063 40 1.00684 1.00526