An olive press extracts oil from olives using mechanical force or modern hydraulic systems
An olive press is a machine that squeezes oil out of olives. The oldest presses used large wooden or stone screws turned by hand or animal power; modern ones use hydraulic pressure to do the same job faster and with less labour. The oil that comes out is what you buy as olive oil. The solid matter left behind — called pomace — can be pressed again to extract more oil, or used for other purposes like animal feed or fuel.
The type of press used affects how much oil comes out of the olives and what the oil tastes like. A stone mill that grinds olives slowly produces different results than a steel hammer mill that works quickly. Temperature control during pressing also matters: if the olives get too warm, some flavour compounds break down. This is why producers who want to make extra virgin olive oil — the highest grade — are careful about how fast and hot they press.
Key Takeaways
- Traditional presses use a large screw or lever to squeeze olives; modern presses use hydraulic pumps to explore pressure more evenly and quickly.
- The grinding step before pressing breaks down the olive flesh so oil can separate from the solid parts more easily.
- Pressing temperature affects oil quality: slower, cooler pressing preserves more flavour but produces less oil per olive.
- The leftover solid matter from pressing can be pressed again or used for animal feed, biofuel, or compost.
How a traditional olive press works
A traditional press starts with a large wooden or metal screw mounted vertically over a circular stone or wooden base. Olives that have been ground into a paste are placed in woven baskets or cloth mats stacked on top of each other on the base. As the screw turns — powered by hand, animals, or later by motors — it pushes down on the stack with increasing force. The oil runs out through gaps in the baskets and collects in channels carved into the base, flowing into a container below.
This method is slow and labour-intensive, but it produces very clean oil because the solid matter stays in the baskets and does not mix with the liquid. Many small producers and heritage operations still use versions of this design because the slow, gentle pressure is thought to preserve flavour. The downside is that a lot of oil stays trapped in the pomace — the pressed solids — and cannot be recovered without a second pressing or chemical extraction.
How modern hydraulic presses work
A modern hydraulic press replaces the screw with a pump that pushes oil through cylinders, creating very high and very even pressure. The ground olive paste is still placed in baskets or on a conveyor belt, but the pressing happens much faster — sometimes in minutes instead of hours. The pressure can be controlled precisely, so producers can adjust it to get different results from the same batch of olives.
Hydraulic presses are more efficient: they extract more oil from each olive and produce less waste. They also allow producers to press at lower temperatures if they want to, because the pressure does the work instead of heat. However, the higher pressure can push some solid particles into the oil, which is why the oil may need to be filtered afterward if a very clear product is wanted.
The grinding step before pressing
Before any press is used, the olives must be ground or crushed. This breaks down the cell walls of the olive flesh so the oil inside can separate from the solid parts. Traditionally, large stone wheels or millstones rolled over the olives on a flat stone surface. Modern mills use steel hammers or discs spinning at high speed to do the same job in seconds.
The grinding method affects the final oil. A slow stone mill produces a finer, more uniform paste and is gentler on the olives, which some producers believe preserves delicate flavours. A fast steel hammer mill heats the olives more through friction, which can bring out different flavours but may damage some of the compounds that make extra virgin oil special. The temperature during grinding is one reason why producers who make premium oil often use cooler grinding methods and monitor the process carefully.
Temperature control and oil quality
The temperature of the olives and paste during grinding and pressing directly affects the quality and flavour of the oil. Extra virgin olive oil — the highest grade — must be made without heat above 27°C (about 80°F) in most definitions, though some producers aim even lower. At these temperatures, the oil retains more of the compounds that give it colour, flavour, and aroma.
If the olives are pressed warm or the paste is heated during processing, more oil comes out faster, but some of the flavour compounds break down or evaporate. This is why producers making extra virgin oil use slow grinding, cool pressing, and sometimes even refrigerated equipment. Producers making lower grades of olive oil — refined oil or pomace oil — may use higher temperatures because flavour preservation is less important and they want to extract as much oil as possible.
What happens to the leftover solids
After pressing, the solid matter left in the baskets or on the press is called pomace. It still contains some oil — usually 5 to 10 percent by weight. Producers can press it again using a second press, or they can use chemical solvents to extract the remaining oil. Oil made from pomace is called pomace olive oil and is a lower grade than oil pressed directly from whole olives.
Pomace that is not pressed again can be dried and used as animal feed, burned as biofuel, or composted. Some producers sell it to other companies that specialise in extracting oil from it. The water that runs off during pressing — called olive mill wastewater — is a disposal challenge in regions with many olive mills, though some producers use it to irrigate crops or treat it for reuse.
Batch pressing versus continuous pressing
Batch presses work on a fixed amount of olives at a time: the paste goes in, pressure is applied for a set period, the oil is collected, and then the press is emptied and cleaned before the next batch. This method gives producers more control over each batch and is common in small mills and heritage operations.
Continuous presses feed ground olives in at one end and discharge the pomace at the other, with oil flowing out throughout the process. These machines can handle much larger volumes and run for hours without stopping. Most commercial olive oil producers use continuous presses because they are faster and more efficient, though some argue that batch pressing produces better-quality oil because each batch can be monitored and adjusted individually.
Frequently Asked Questions
How much oil does one olive produce?
One olive produces roughly 15 to 20 percent of its weight in oil, though this varies by variety, ripeness, and growing conditions. A mature olive tree might produce 40 to 50 kilograms of olives per year, which yields about 8 to 10 litres of oil. Younger trees produce less, and some varieties are naturally more oily than others.
Why does some olive oil say "cold-pressed"?
"Cold-pressed" means the olives were ground and pressed without added heat and at temperatures below a certain threshold — usually 27°C. This preserves more flavour and aroma. The term does not mean no heat was generated at all; friction from grinding and pressing naturally creates some warmth, but producers control it carefully.
Can you press olives at home?
Yes, but it is difficult without equipment. Small manual presses exist for home use, but they require a lot of physical effort and produce very little oil. Most home producers either buy a small electric press (which costs several hundred dollars) or take their olives to a local mill that presses for a fee or a share of the oil.
What is the difference between extra virgin and regular olive oil?
Extra virgin oil comes from the first pressing of fresh olives, using only mechanical methods and no heat above 27°C. Regular or "light" olive oil is refined, meaning it has been treated with heat and chemicals to remove flavour and colour, then often blended with a small amount of extra virgin oil. Refined oil has a higher smoke point and longer shelf life but less flavour.
Why does olive oil sometimes have sediment at the bottom?
Sediment is usually tiny particles of olive flesh or skin that were not filtered out after pressing. It is harmless and common in unfiltered or lightly filtered oils, especially those made with traditional presses. Some producers filter it out for clarity; others leave it because it carries flavour. Sediment will settle to the bottom over time.