Last night I prepared the samples for the experiment described below.
Actual OG was 1.042 for Sample A and 1.072 for sample B. The yeast used was a pack of S-23 which expired in 2014 (it's been in my fridge since 2013, so it's probably ok). The ~7.5 grams not pitched to the samples was boiled with the wort to provide nutrients.
Hypothesis
Sucrose is nearly 100% fermentable by brewers yeast. The typical attenuation percentage of brewers yeast applies to a typical all-malt wort, but not to a wort with increased amounts of simple sugars. Increasing the original gravity of a wort by adding sucrose will therefore not increase the final gravity of the beer.
Test methodology
Two samples A and B, will be prepared.
1 liter of wort will be prepared from water and dried malt extract. DME will be added to boiling water to reach a specific gravity of 1.040. Dry brewers yeast will be added to the boil to serve as yeast nutrient. After boiling for 5 minutes the wort will be cooled and aerated. An equal amount of this wort will be transferred to two fermenters, labeled A and B. Care will be taken to transfer an equal amount of trub to both fermenters.
Sample A: No modifications.
Sample B: A pasteurized solution of sucrose in water will be added to the sample to reach a specific gravity of 1.070.
2g of dry yeast will be sprinkled on top of each sample.
Sample A and B will be fermented at the same temperature until fermentation is complete. Fermentation will be considered complete when SG has remained unchanged in both samples for >=48 hours.
The final gravity of the samples will then be measured using the same hydrometer.
Evaluation of results
If the hypothesis is correct the following observation is expected:
The final gravity of Sample A will be higher than or equal to the final gravity of Sample B.
Potential problems with the experiment:
1. If the OG of the sample is too high, the alcohol tolerance of the yeast may influence, the result. I expect 1.070 be low enough that this will not influence the results.
2. The yeast may become “lazy” feeding on simple sugars and not ferment the more complex sugars from the DME. Another experiment including a sample where the sucrose is added after the yeast has fermented the DME should be able to show if this is the case.
3. If the FG of the two samples are similar, measurment errors may influence the result. With 30 points seperating the OG of the samples, I don't expect this to be a problem.
4. If either batch gets infected with a wild yeast, bacteria or even a different strain of brewers yeast the results will be invalid. I therefore cleaned and sanetized as I would normally do for a starter.
5. Underpitching may cause low attenuation and invalidate the results. Despite the age of the yeast, I don't think it will influence the result as I pitched a large quantity relative to the amount of wort and the yeast has been stored cold. I do not expect overpitching to influence the experiment.