Adding Water at the Malaxer Cost Yield and Phenols
Adding water while the olive paste is mixed, a routine trick in mills to squeeze out more oil, actually reduced the yield and cost the oil some of its antioxidants in a new Spanish study. Talc, the other common processing aid, did raise yield. Here is what researchers at the University of Extremadura measured, and what it means for the oil that comes out of the mill.
What the study did
The work comes from the food technology department at the University of Extremadura and has just been published in the European Journal of Lipid Science and Technology, under the title “Effect of talc and water addition on olive oil quality and antioxidants”. The team, led by Ana Carrapiso with Amparo García, María Jesús Petrón and Lourdes Martín, worked with two varieties: Picual, the Spanish workhorse that has been studied for years, and Carrasqueña, an Extremadura variety examined this way for the first time.
Both were processed on a laboratory scale system, with and without added water, and with and without talc, so the effect of each could be measured against the same fruit.
What it found
| Added during mixing | Effect on yield | Effect on the oil |
|---|---|---|
| Water | Yield and extractability went down | Higher peroxide value, lower total phenols, color barely changed |
| Talc | Yield and extractability went up | Lower peroxide value, less alpha-tocopherol, clearly greener and lighter color |
The water result is the surprise. Mills add water at the malaxer, the slow mixing stage before the paste goes to the centrifuge, precisely to get more oil out. In this trial it did the opposite in both varieties, and the oil came out with fewer phenols, the compounds behind the bitterness, the pepper at the back of the throat and much of the oil’s stability. Free acidity, the number everyone quotes, was not significantly affected, which is a reminder that acidity alone tells you very little about how an oil was made.
Earlier work had already warned against adding water to fruit from irrigated groves, where the olives arrive wet enough as it is. What is new here is that the same warning applies to rainfed fruit.
Why it matters beyond the laboratory
- Phenols dissolve in water. Every liter added at the malaxer gives them somewhere to go, and they leave with the waste water rather than staying in the oil.
- Less added water means less vegetation water to treat or spread, and less energy used. That is the argument for the two-phase decanter, which uses little or no added water, over the older three-phase system.
- Talc is a mined mineral used as a processing aid. It helps the tiny oil droplets join up in a difficult paste, and it is separated out with the solids rather than ending up in the bottle.
- None of this shows on a label. Two oils from the same grove and the same week can differ in phenols simply because of what the miller did in the malaxer.
Ask a miller how much water he adds and you learn more about his oil than any marketing sheet will tell you. Water is the cheap way to chase yield when a paste is hard to work, and on a busy day it also speeds the line. The cost is invisible on the invoice and obvious in the glass: a thinner, softer oil that fades faster. The mills that charge more for careful work are mostly selling you restraint, not equipment.
Sources
- Carrapiso, García, Petrón and Martín: Effect of talc and water addition on olive oil quality and antioxidants, European Journal of Lipid Science and Technology, vol. 115 (2013)
- Olive Oil Times: Adding Water During Malaxation Decreases Yield and Quality (April 8, 2013)