An ephah
is equal to somewhere between thirteen and twenty-three litres. The offerer is to present a tenth of an ephah for sacrifice. According to Numbers 28:5, this is the minimum amount to be offered on the altar. The worshipper is not required to add oil or frankincense to the grain. These elements were often used within the context of festive celebrations; conversely, this offering dealt with guilt and would have been inappropriate. Furthermore, omitting these items keeps the cost of the sacrifice low.
11 “But if he cannot afford two turtledoves or two pigeons, then he shall bring as his offering for the sin that he has committed a tenth of an ephah of fine flour for a sin offering. He shall put no oil on it and shall put no frankincense on it, for it is a sin offering.