Here is a way you could set up Odoo that might work for you:

Since Odoo can't convert between Weight and Volume, you will need to create your own Unit of Measure category that contains the Weight measurements that you use for the seeds and the Volume measurements that you use for the oil.  In this example, I have used seed lb(s) and oil fluid oz(s) within a new Category called Pressing.

Create a Bill of Materials using the average measure of seeds to produce the average measure of oil and enter what you actually consume and produce during each Manufacturing Order.

Here, on average we get 475 oz from 30 lbs of Kernels.

Manufacturing Orders can be created in Odoo for 475oz, or any higher amount, including other units (like oil gallons) as long as you enter them and the conversion factors. 

For an example Manufacturing Order to press 1 Gallon:

You simply adjust the actual produced amount in the Manufacturing Order:

In this example, the press resulted in 120 oz from 8 lbs of kernels.  You can that after we changed the 128 to 120, Odoo readjusted the expected quantity of kernels needed to match the Bill of Materials but it will still let us enter what we actually used when we click PRODUCE:

Inventory Moves for this Manufacturing Order show the expected 7.58 seed lb(s) plus the extra 0.42 seed lbs (for a total of 8 seed lbs) Consumed and the 120 fluid oil oz(s) produced:

Cost Analysis (products only, because we are not using Work Orders for machine or worker time) for this Manufacturing Order shows a unit cost of 9 cents per fluid oil ounce (based on a cost of $1.35 per seed pound of kernels) :

This approach gives you:

• a single Bill of Materials for Pressed Oil

• a way to generate and/or enter Manufacturing Orders for any initial estimated quantity

• a place to record actual production

• a place to record actual consumption

• correct Inventory Moves

• correct Pricing