Here is what Srila Prabhupada says about how to offer bhoga to the Lord: Letter to Aniruddha Das, June 16, 1968
"So the purport is that everything should be offered very cleanly and pure things should be given. If a preparation is cooked all together, then offer all together. But if it is prepared separately, then the milk, the sugar and the cereal should be offered separately. But if the milk, sugar and grains are all cooked together, that can be done. (Everything should be prepared very carefully and cleanly within the groups of foods listed. And nothing should ever be eaten before offering to the Lord. Best thing is to prepare separately each preparation. No, food which has been offered should never be put back into the refrigerator with the unoffered foods, or brought back into the kitchen. You should prepare as much as can be consumed, and after offering, nothing should be put back in the refrigerator, or kitchen. Refrigerator should always be very cleansed and pure. Everyone should be careful to make only as much as they can eat; they cannot keep any leftovers in refrigerator. I know this is a practice in your country, but in the temples or at homes of any Krishna Consciousness persons, a person should not indulge in such unclean habits. If there is any food extra, that should be kept separately; and if there is a separate refrigerator, not within the kitchen and not having in it any unoffered foods, then you may have such special refrigerator for leftover prasadam. But it cannot be kept within the same refrigerator as the unoffered, unprepared foods. That cannot be. One should never eat within the kitchen, there is ample place to eat so why should one eat in the kitchen? Kitchen should be considered as good as the Lord's room, and nobody should wear shoes in the kitchen, smelling and tasting of foods being prepared for the Lord should never be done, talking within the kitchen should be only what is necessary for preparing the prasadam, or about the Lord, and dirty dishes (those taken from kitchen and eaten from) should not be brought back into the kitchen (but if there is no other place to wash them, then they should be put into sink and washed immediately.), hands should always be washed when preparing prasadam, and in this way, everything shall be prepared very cleanly and pure.)"